[3/4] LoongArch: Add support for kernel relocation

  arch/loongarch/kernel/relocate.c contains the functions necessary to
relocate the kernel elsewhere in memory.

The kernel makes a copy of itself at the new address. It uses the
relocation table inserted by the relocs tool to fix symbol references
within the new image.

If copy/relocation is successful then the entry point of the new kernel
is returned, otherwise fall back to starting the kernel in place.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
---
 arch/loongarch/Kconfig              | 15 +++++
 arch/loongarch/Makefile             |  5 ++
 arch/loongarch/kernel/Makefile      |  2 +
 arch/loongarch/kernel/head.S        | 18 ++++++
 arch/loongarch/kernel/relocate.c    | 96 +++++++++++++++++++++++++++++
 arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
 6 files changed, 145 insertions(+), 2 deletions(-)
 create mode 100644 arch/loongarch/kernel/relocate.c
  

Hi Youling,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.2-rc3 next-20230109]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Youling-Tang/LoongArch-Use-trampoline-for-exception-handlers-and-kill-la-abs/20230109-171344
patch link:    https://lore.kernel.org/r/1673255274-18238-4-git-send-email-tangyouling%40loongson.cn
patch subject: [PATCH 3/4] LoongArch: Add support for kernel relocation
config: loongarch-allmodconfig
compiler: loongarch64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/35b3031ab84fc4832dd66a381f37fb2dcec8e5c1
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Youling-Tang/LoongArch-Use-trampoline-for-exception-handlers-and-kill-la-abs/20230109-171344
        git checkout 35b3031ab84fc4832dd66a381f37fb2dcec8e5c1
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash arch/loongarch/kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

Note: functions only called from assembly code should be annotated with the asmlinkage attribute
All warnings (new ones prefixed by >>):

>> arch/loongarch/kernel/relocate.c:44:14: warning: no previous prototype for 'relocate_kernel' [-Wmissing-prototypes]
      44 | void *__init relocate_kernel(void)
         |              ^~~~~~~~~~~~~~~
   arch/loongarch/kernel/relocate.c: In function 'relocate_kernel':
>> arch/loongarch/kernel/relocate.c:82:48: warning: assignment to 'Elf64_Addr' {aka 'long long unsigned int'} from 'void *' makes integer from pointer without a cast [-Wint-conversion]
      82 |                                 relocated_addr = RELOCATED(relocated_addr);
         |                                                ^
   arch/loongarch/kernel/relocate.c:94:1: warning: label 'out' defined but not used [-Wunused-label]
      94 | out:
         | ^~~
   arch/loongarch/kernel/relocate.c:50:13: warning: unused variable 'res' [-Wunused-variable]
      50 |         int res = 1;
         |             ^~~


vim +/relocate_kernel +44 arch/loongarch/kernel/relocate.c

    43	
  > 44	void *__init relocate_kernel(void)
    45	{
    46		Elf64_Rela *rela, *rela_end;
    47		void *loc_new;
    48		unsigned long kernel_length;
    49		long offset = 0;
    50		int res = 1;
    51		/* Default to original kernel entry point */
    52		void *kernel_entry = start_kernel;
    53	
    54		kernel_length = (long)(_end) - (long)(_text);
    55	
    56		loc_new = determine_relocation_address();
    57	
    58		/* Sanity check relocation address */
    59		if (relocation_addr_valid(loc_new))
    60			offset = (unsigned long)loc_new - (unsigned long)(_text);
    61	
    62		if (offset) {
    63			/* Copy the kernel to it's new location */
    64			memcpy(loc_new, _text, kernel_length);
    65	
    66			/* Sync the caches ready for execution of new kernel */
    67			__asm__ __volatile__ (
    68				"ibar 0 \t\n"
    69				"dbar 0 \t\n");
    70	
    71			rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
    72			rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
    73	
    74			for ( ; rela < rela_end; rela++) {
    75				Elf64_Addr addr = rela->r_offset;
    76				Elf64_Addr relocated_addr = rela->r_addend;
    77	
    78				if (rela->r_info != R_LARCH_RELATIVE)
    79					continue;
    80	
    81				if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
  > 82					relocated_addr = RELOCATED(relocated_addr);
  

On 01/09/2023 05:07 PM, Youling Tang wrote:
> arch/loongarch/kernel/relocate.c contains the functions necessary to
> relocate the kernel elsewhere in memory.
>
> The kernel makes a copy of itself at the new address. It uses the
> relocation table inserted by the relocs tool to fix symbol references
> within the new image.
>
> If copy/relocation is successful then the entry point of the new kernel
> is returned, otherwise fall back to starting the kernel in place.
>
> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
> ---
>  arch/loongarch/Kconfig              | 15 +++++
>  arch/loongarch/Makefile             |  5 ++
>  arch/loongarch/kernel/Makefile      |  2 +
>  arch/loongarch/kernel/head.S        | 18 ++++++
>  arch/loongarch/kernel/relocate.c    | 96 +++++++++++++++++++++++++++++
>  arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>  6 files changed, 145 insertions(+), 2 deletions(-)
>  create mode 100644 arch/loongarch/kernel/relocate.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 9cc8b84f7eb0..089a4695b1b3 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -48,6 +48,7 @@ config LOONGARCH
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_SUPPORTS_HUGETLBFS
>  	select ARCH_SUPPORTS_NUMA_BALANCING
> +	select SYS_SUPPORTS_RELOCATABLE
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF
>  	select ARCH_USE_QUEUED_RWLOCKS
> @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER
>  config AS_HAS_EXPLICIT_RELOCS
>  	def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
>
> +config SYS_SUPPORTS_RELOCATABLE
> +	bool
> +	help
> +	  Selected if the platform supports relocating the kernel.
> +
>  menu "Kernel type and options"
>
>  source "kernel/Kconfig.hz"
> @@ -474,6 +480,15 @@ config PHYSICAL_START
>  	  specified in the "crashkernel=YM@XM" command line boot parameter
>  	  passed to the panic-ed kernel).
>
> +config RELOCATABLE
> +	bool "Relocatable kernel"
> +	depends on SYS_SUPPORTS_RELOCATABLE
> +	help
> +	  This builds the kernel as a Position Independent Executable (PIE),
> +	  which retains all relocation metadata required to relocate the
> +	  kernel binary at runtime to a different virtual address than the
> +	  address it was linked at.
> +
>  config SECCOMP
>  	bool "Enable seccomp to safely compute untrusted bytecode"
>  	depends on PROC_FS
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 4402387d2755..27b5a70ff31c 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE		+= -Wa,-mla-global-with-abs
>  KBUILD_CFLAGS_MODULE		+= -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
>  endif
>
> +ifeq ($(CONFIG_RELOCATABLE),y)
> +LDFLAGS_vmlinux			+= -static -pie --no-dynamic-linker -z notext
> +KBUILD_CFLAGS_KERNEL		+= -fPIE
> +endif
> +
>  cflags-y += -ffreestanding
>  cflags-y += $(call cc-option, -mno-check-zero-division)
>
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index fcaa024a685e..33787d22e6f4 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -31,6 +31,8 @@ endif
>  obj-$(CONFIG_MODULES)		+= module.o module-sections.o
>  obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
>
> +obj-$(CONFIG_RELOCATABLE)	+= relocate.o
> +
>  obj-$(CONFIG_PROC_FS)		+= proc.o
>
>  obj-$(CONFIG_SMP)		+= smp.o
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index e8a4bf9d7599..6db1549177ad 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
>  	PTR_ADD		sp, sp, tp
>  	set_saved_sp	sp, t0, t1
>
> +#ifdef CONFIG_RELOCATABLE
> +	/* Copy kernel and apply the relocations */
> +	bl		relocate_kernel
> +
> +	/* Repoint the sp into the new kernel image */
> +	PTR_LI		sp, (_THREAD_SIZE - 32 - PT_SIZE)
> +	PTR_ADD		sp, sp, tp
> +	set_saved_sp	sp, t0, t1
> +	PTR_ADDI	sp, sp, -4 * SZREG      # init stack pointer
PTR_ADDI	sp, sp, -4 * SZREG      # init stack pointer

This line needs to be removed.

> +
> +	/*
> +	 * relocate_kernel returns the entry point either
> +	 * in the relocated kernel or the original if for
> +	 * some reason relocation failed.
> +	*/
> +	jr		a0
> +#else
>  	bl		start_kernel
> +#endif
>  	ASM_BUG()
>
>  SYM_CODE_END(kernel_entry)
> diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
> new file mode 100644
> index 000000000000..a58551c0698d
> --- /dev/null
> +++ b/arch/loongarch/kernel/relocate.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for Kernel relocation at boot time
> + *
> + * Copyright (C) 2023 Loongson Technology Corporation Limited
> + */
> +
> +#include <linux/elf.h>
> +#include <linux/kernel.h>
> +#include <linux/start_kernel.h>
> +#include <linux/printk.h>
> +#include <linux/panic_notifier.h>
> +#include <asm/bootinfo.h>
> +#include <asm/inst.h>
> +#include <asm/sections.h>
> +
> +#define RELOCATED(x) ((void *)((long)x + offset))
> +
> +extern long __rela_dyn_start;
> +extern long __rela_dyn_end;
> +
> +/*
> + * Choose a new address for the kernel, for now we'll hard
> + * code the destination.
> + */
> +static inline void __init *determine_relocation_address(void)
> +{
> +	return (void *)(CACHE_BASE + 0x02000000);
> +}
> +
> +static inline int __init relocation_addr_valid(void *loc_new)
> +{
> +	if ((unsigned long)loc_new & 0x0000ffff) {
> +		/* Inappropriately aligned new location */
> +		return 0;
> +	}
> +	if ((unsigned long)loc_new < (unsigned long)_end) {
> +		/* New location overlaps original kernel */
> +		return 0;
> +	}
> +	return 1;
> +}
> +
> +void *__init relocate_kernel(void)
> +{
> +	Elf64_Rela *rela, *rela_end;
> +	void *loc_new;
> +	unsigned long kernel_length;
> +	long offset = 0;
> +	int res = 1;
> +	/* Default to original kernel entry point */
> +	void *kernel_entry = start_kernel;
> +
> +	kernel_length = (long)(_end) - (long)(_text);
> +
> +	loc_new = determine_relocation_address();
> +
> +	/* Sanity check relocation address */
> +	if (relocation_addr_valid(loc_new))
> +		offset = (unsigned long)loc_new - (unsigned long)(_text);
> +
> +	if (offset) {
> +		/* Copy the kernel to it's new location */
> +		memcpy(loc_new, _text, kernel_length);
> +
> +		/* Sync the caches ready for execution of new kernel */
> +		__asm__ __volatile__ (
> +			"ibar 0 \t\n"
> +			"dbar 0 \t\n");
> +
> +		rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
> +		rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
> +
> +		for ( ; rela < rela_end; rela++) {
> +			Elf64_Addr addr = rela->r_offset;
> +			Elf64_Addr relocated_addr = rela->r_addend;
> +
> +			if (rela->r_info != R_LARCH_RELATIVE)
> +				continue;
> +
> +			if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
> +				relocated_addr = RELOCATED(relocated_addr);
> +
> +			*(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
> +
> +		}
> +
> +		/* The current thread is now within the relocated image */
> +		__current_thread_info = RELOCATED(__current_thread_info);
> +
> +		/* Return the new kernel's entry point */
> +		kernel_entry = RELOCATED(start_kernel);
> +	}
> +out:
> +	return kernel_entry;
> +}
> diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
> index 733b16e8d55d..aec0b6567d24 100644
> --- a/arch/loongarch/kernel/vmlinux.lds.S
> +++ b/arch/loongarch/kernel/vmlinux.lds.S
> @@ -70,6 +70,8 @@ SECTIONS
>  	.plt : ALIGN(16) { *(.plt) }
>  	.got.plt : ALIGN(16) { *(.got.plt) }
>
> +	.data.rel : { *(.data.rel*) }
> +
>  	. = ALIGN(PECOFF_SEGMENT_ALIGN);
>  	__init_begin = .;
>  	__inittext_begin = .;
> @@ -93,8 +95,6 @@ SECTIONS
>  	PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
>  #endif
>
> -	.rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
> -
>  	.init.bss : {
>  		*(.init.bss)
>  	}
> @@ -107,6 +107,12 @@ SECTIONS
>  	RO_DATA(4096)
>  	RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
>
> +	.rela.dyn : ALIGN(8) {
> +		__rela_dyn_start = .;
> +		 *(.rela.dyn) *(.rela*)
> +		__rela_dyn_end = .;
> +	}
> +
>  	.sdata : {
>  		*(.sdata)
>  	}
> @@ -133,6 +139,7 @@ SECTIONS
>
>  	DISCARDS
>  	/DISCARD/ : {
> +		*(.dynamic .dynsym .dynstr .hash .gnu.hash)
>  		*(.gnu.attributes)
>  		*(.options)
>  		*(.eh_frame)
>
  

On 2023-01-09 17:07, Youling Tang wrote:
> arch/loongarch/kernel/relocate.c contains the functions necessary to
> relocate the kernel elsewhere in memory.
>
> The kernel makes a copy of itself at the new address. It uses the
> relocation table inserted by the relocs tool to fix symbol references
> within the new image.
>
> If copy/relocation is successful then the entry point of the new kernel
> is returned, otherwise fall back to starting the kernel in place.
>
> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
> ---
>   arch/loongarch/Kconfig              | 15 +++++
>   arch/loongarch/Makefile             |  5 ++
>   arch/loongarch/kernel/Makefile      |  2 +
>   arch/loongarch/kernel/head.S        | 18 ++++++
>   arch/loongarch/kernel/relocate.c    | 96 +++++++++++++++++++++++++++++
>   arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>   6 files changed, 145 insertions(+), 2 deletions(-)
>   create mode 100644 arch/loongarch/kernel/relocate.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 9cc8b84f7eb0..089a4695b1b3 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -48,6 +48,7 @@ config LOONGARCH
>   	select ARCH_SUPPORTS_ATOMIC_RMW
>   	select ARCH_SUPPORTS_HUGETLBFS
>   	select ARCH_SUPPORTS_NUMA_BALANCING
> +	select SYS_SUPPORTS_RELOCATABLE
>   	select ARCH_USE_BUILTIN_BSWAP
>   	select ARCH_USE_CMPXCHG_LOCKREF
>   	select ARCH_USE_QUEUED_RWLOCKS
> @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER
>   config AS_HAS_EXPLICIT_RELOCS
>   	def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
>   
> +config SYS_SUPPORTS_RELOCATABLE
> +	bool
> +	help
> +	  Selected if the platform supports relocating the kernel.
> +
>   menu "Kernel type and options"
>   
>   source "kernel/Kconfig.hz"
> @@ -474,6 +480,15 @@ config PHYSICAL_START
>   	  specified in the "crashkernel=YM@XM" command line boot parameter
>   	  passed to the panic-ed kernel).
>   
> +config RELOCATABLE
> +	bool "Relocatable kernel"
> +	depends on SYS_SUPPORTS_RELOCATABLE
> +	help
> +	  This builds the kernel as a Position Independent Executable (PIE),
> +	  which retains all relocation metadata required to relocate the
> +	  kernel binary at runtime to a different virtual address than the
> +	  address it was linked at.
> +
>   config SECCOMP
>   	bool "Enable seccomp to safely compute untrusted bytecode"
>   	depends on PROC_FS
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 4402387d2755..27b5a70ff31c 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE		+= -Wa,-mla-global-with-abs
>   KBUILD_CFLAGS_MODULE		+= -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
>   endif
>   
> +ifeq ($(CONFIG_RELOCATABLE),y)
> +LDFLAGS_vmlinux			+= -static -pie --no-dynamic-linker -z notext
> +KBUILD_CFLAGS_KERNEL		+= -fPIE
> +endif
> +
>   cflags-y += -ffreestanding
>   cflags-y += $(call cc-option, -mno-check-zero-division)
>   
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index fcaa024a685e..33787d22e6f4 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -31,6 +31,8 @@ endif
>   obj-$(CONFIG_MODULES)		+= module.o module-sections.o
>   obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
>   
> +obj-$(CONFIG_RELOCATABLE)	+= relocate.o
> +
>   obj-$(CONFIG_PROC_FS)		+= proc.o
>   
>   obj-$(CONFIG_SMP)		+= smp.o
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index e8a4bf9d7599..6db1549177ad 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
>   	PTR_ADD		sp, sp, tp
>   	set_saved_sp	sp, t0, t1
>   
> +#ifdef CONFIG_RELOCATABLE
> +	/* Copy kernel and apply the relocations */
> +	bl		relocate_kernel
> +
> +	/* Repoint the sp into the new kernel image */
> +	PTR_LI		sp, (_THREAD_SIZE - 32 - PT_SIZE)
> +	PTR_ADD		sp, sp, tp
> +	set_saved_sp	sp, t0, t1
> +	PTR_ADDI	sp, sp, -4 * SZREG      # init stack pointer
> +
> +	/*
> +	 * relocate_kernel returns the entry point either
> +	 * in the relocated kernel or the original if for
> +	 * some reason relocation failed.
> +	*/
> +	jr		a0
> +#else
>   	bl		start_kernel
> +#endif
>   	ASM_BUG()
>   
>   SYM_CODE_END(kernel_entry)
> diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
> new file mode 100644
> index 000000000000..a58551c0698d
> --- /dev/null
> +++ b/arch/loongarch/kernel/relocate.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for Kernel relocation at boot time
> + *
> + * Copyright (C) 2023 Loongson Technology Corporation Limited
> + */
> +
> +#include <linux/elf.h>
> +#include <linux/kernel.h>
> +#include <linux/start_kernel.h>
> +#include <linux/printk.h>
> +#include <linux/panic_notifier.h>
> +#include <asm/bootinfo.h>
> +#include <asm/inst.h>
> +#include <asm/sections.h>
> +
> +#define RELOCATED(x) ((void *)((long)x + offset))
> +
> +extern long __rela_dyn_start;
> +extern long __rela_dyn_end;
> +
> +/*
> + * Choose a new address for the kernel, for now we'll hard
> + * code the destination.
> + */
> +static inline void __init *determine_relocation_address(void)
> +{
> +	return (void *)(CACHE_BASE + 0x02000000);
> +}
> +
> +static inline int __init relocation_addr_valid(void *loc_new)
> +{
> +	if ((unsigned long)loc_new & 0x0000ffff) {

Hi, Youling,


12bits-aligned is OK as actually R_LARCH_PCALA_LO12 is absolute.


BTW, I think the relocation of kernel looks like the '.so' solve its
Relocs at user space so that it can be placed any legal address. The
address is determined first, and relocation make it works on that address.
Thus, this patch always relocate kernel to 'CACHE_BASE + 0x02000000'
makes me puzzled. I think the relocation only works when the kernel
runtime address is different from the link-time address.


Thanks,
Jinyang


> +		/* Inappropriately aligned new location */
> +		return 0;
> +	}
> +	if ((unsigned long)loc_new < (unsigned long)_end) {
> +		/* New location overlaps original kernel */
> +		return 0;
> +	}
> +	return 1;
> +}
> +
> +void *__init relocate_kernel(void)
> +{
> +	Elf64_Rela *rela, *rela_end;
> +	void *loc_new;
> +	unsigned long kernel_length;
> +	long offset = 0;
> +	int res = 1;
> +	/* Default to original kernel entry point */
> +	void *kernel_entry = start_kernel;
> +
> +	kernel_length = (long)(_end) - (long)(_text);
> +
> +	loc_new = determine_relocation_address();
> +
> +	/* Sanity check relocation address */
> +	if (relocation_addr_valid(loc_new))
> +		offset = (unsigned long)loc_new - (unsigned long)(_text);
> +
> +	if (offset) {
> +		/* Copy the kernel to it's new location */
> +		memcpy(loc_new, _text, kernel_length);
> +
> +		/* Sync the caches ready for execution of new kernel */
> +		__asm__ __volatile__ (
> +			"ibar 0 \t\n"
> +			"dbar 0 \t\n");
> +
> +		rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
> +		rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
> +
> +		for ( ; rela < rela_end; rela++) {
> +			Elf64_Addr addr = rela->r_offset;
> +			Elf64_Addr relocated_addr = rela->r_addend;
> +
> +			if (rela->r_info != R_LARCH_RELATIVE)
> +				continue;
> +
> +			if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
> +				relocated_addr = RELOCATED(relocated_addr);
> +
> +			*(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
> +
> +		}
> +
> +		/* The current thread is now within the relocated image */
> +		__current_thread_info = RELOCATED(__current_thread_info);
> +
> +		/* Return the new kernel's entry point */
> +		kernel_entry = RELOCATED(start_kernel);
> +	}
> +out:
> +	return kernel_entry;
> +}
> diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
> index 733b16e8d55d..aec0b6567d24 100644
> --- a/arch/loongarch/kernel/vmlinux.lds.S
> +++ b/arch/loongarch/kernel/vmlinux.lds.S
> @@ -70,6 +70,8 @@ SECTIONS
>   	.plt : ALIGN(16) { *(.plt) }
>   	.got.plt : ALIGN(16) { *(.got.plt) }
>   
> +	.data.rel : { *(.data.rel*) }
> +
>   	. = ALIGN(PECOFF_SEGMENT_ALIGN);
>   	__init_begin = .;
>   	__inittext_begin = .;
> @@ -93,8 +95,6 @@ SECTIONS
>   	PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
>   #endif
>   
> -	.rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
> -
>   	.init.bss : {
>   		*(.init.bss)
>   	}
> @@ -107,6 +107,12 @@ SECTIONS
>   	RO_DATA(4096)
>   	RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
>   
> +	.rela.dyn : ALIGN(8) {
> +		__rela_dyn_start = .;
> +		 *(.rela.dyn) *(.rela*)
> +		__rela_dyn_end = .;
> +	}
> +
>   	.sdata : {
>   		*(.sdata)
>   	}
> @@ -133,6 +139,7 @@ SECTIONS
>   
>   	DISCARDS
>   	/DISCARD/ : {
> +		*(.dynamic .dynsym .dynstr .hash .gnu.hash)
>   		*(.gnu.attributes)
>   		*(.options)
>   		*(.eh_frame)
  

Hi, Jinyang

On 01/14/2023 02:54 PM, Jinyang He wrote:
>
> On 2023-01-09 17:07, Youling Tang wrote:
>> arch/loongarch/kernel/relocate.c contains the functions necessary to
>> relocate the kernel elsewhere in memory.
>>
>> The kernel makes a copy of itself at the new address. It uses the
>> relocation table inserted by the relocs tool to fix symbol references
>> within the new image.
>>
>> If copy/relocation is successful then the entry point of the new kernel
>> is returned, otherwise fall back to starting the kernel in place.
>>
>> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
>> ---
>>   arch/loongarch/Kconfig              | 15 +++++
>>   arch/loongarch/Makefile             |  5 ++
>>   arch/loongarch/kernel/Makefile      |  2 +
>>   arch/loongarch/kernel/head.S        | 18 ++++++
>>   arch/loongarch/kernel/relocate.c    | 96 +++++++++++++++++++++++++++++
>>   arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>>   6 files changed, 145 insertions(+), 2 deletions(-)
>>   create mode 100644 arch/loongarch/kernel/relocate.c
>>
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index 9cc8b84f7eb0..089a4695b1b3 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -48,6 +48,7 @@ config LOONGARCH
>>       select ARCH_SUPPORTS_ATOMIC_RMW
>>       select ARCH_SUPPORTS_HUGETLBFS
>>       select ARCH_SUPPORTS_NUMA_BALANCING
>> +    select SYS_SUPPORTS_RELOCATABLE
>>       select ARCH_USE_BUILTIN_BSWAP
>>       select ARCH_USE_CMPXCHG_LOCKREF
>>       select ARCH_USE_QUEUED_RWLOCKS
>> @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER
>>   config AS_HAS_EXPLICIT_RELOCS
>>       def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
>>   +config SYS_SUPPORTS_RELOCATABLE
>> +    bool
>> +    help
>> +      Selected if the platform supports relocating the kernel.
>> +
>>   menu "Kernel type and options"
>>     source "kernel/Kconfig.hz"
>> @@ -474,6 +480,15 @@ config PHYSICAL_START
>>         specified in the "crashkernel=YM@XM" command line boot parameter
>>         passed to the panic-ed kernel).
>>   +config RELOCATABLE
>> +    bool "Relocatable kernel"
>> +    depends on SYS_SUPPORTS_RELOCATABLE
>> +    help
>> +      This builds the kernel as a Position Independent Executable (PIE),
>> +      which retains all relocation metadata required to relocate the
>> +      kernel binary at runtime to a different virtual address than the
>> +      address it was linked at.
>> +
>>   config SECCOMP
>>       bool "Enable seccomp to safely compute untrusted bytecode"
>>       depends on PROC_FS
>> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
>> index 4402387d2755..27b5a70ff31c 100644
>> --- a/arch/loongarch/Makefile
>> +++ b/arch/loongarch/Makefile
>> @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE        +=
>> -Wa,-mla-global-with-abs
>>   KBUILD_CFLAGS_MODULE        += -fplt
>> -Wa,-mla-global-with-abs,-mla-local-with-abs
>>   endif
>>   +ifeq ($(CONFIG_RELOCATABLE),y)
>> +LDFLAGS_vmlinux            += -static -pie --no-dynamic-linker -z notext
>> +KBUILD_CFLAGS_KERNEL        += -fPIE
>> +endif
>> +
>>   cflags-y += -ffreestanding
>>   cflags-y += $(call cc-option, -mno-check-zero-division)
>>   diff --git a/arch/loongarch/kernel/Makefile
>> b/arch/loongarch/kernel/Makefile
>> index fcaa024a685e..33787d22e6f4 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -31,6 +31,8 @@ endif
>>   obj-$(CONFIG_MODULES)        += module.o module-sections.o
>>   obj-$(CONFIG_STACKTRACE)    += stacktrace.o
>>   +obj-$(CONFIG_RELOCATABLE)    += relocate.o
>> +
>>   obj-$(CONFIG_PROC_FS)        += proc.o
>>     obj-$(CONFIG_SMP)        += smp.o
>> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
>> index e8a4bf9d7599..6db1549177ad 100644
>> --- a/arch/loongarch/kernel/head.S
>> +++ b/arch/loongarch/kernel/head.S
>> @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry)            # kernel
>> entry point
>>       PTR_ADD        sp, sp, tp
>>       set_saved_sp    sp, t0, t1
>>   +#ifdef CONFIG_RELOCATABLE
>> +    /* Copy kernel and apply the relocations */
>> +    bl        relocate_kernel
>> +
>> +    /* Repoint the sp into the new kernel image */
>> +    PTR_LI        sp, (_THREAD_SIZE - 32 - PT_SIZE)
>> +    PTR_ADD        sp, sp, tp
>> +    set_saved_sp    sp, t0, t1
>> +    PTR_ADDI    sp, sp, -4 * SZREG      # init stack pointer
>> +
>> +    /*
>> +     * relocate_kernel returns the entry point either
>> +     * in the relocated kernel or the original if for
>> +     * some reason relocation failed.
>> +    */
>> +    jr        a0
>> +#else
>>       bl        start_kernel
>> +#endif
>>       ASM_BUG()
>>     SYM_CODE_END(kernel_entry)
>> diff --git a/arch/loongarch/kernel/relocate.c
>> b/arch/loongarch/kernel/relocate.c
>> new file mode 100644
>> index 000000000000..a58551c0698d
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/relocate.c
>> @@ -0,0 +1,96 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Support for Kernel relocation at boot time
>> + *
>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>> + */
>> +
>> +#include <linux/elf.h>
>> +#include <linux/kernel.h>
>> +#include <linux/start_kernel.h>
>> +#include <linux/printk.h>
>> +#include <linux/panic_notifier.h>
>> +#include <asm/bootinfo.h>
>> +#include <asm/inst.h>
>> +#include <asm/sections.h>
>> +
>> +#define RELOCATED(x) ((void *)((long)x + offset))
>> +
>> +extern long __rela_dyn_start;
>> +extern long __rela_dyn_end;
>> +
>> +/*
>> + * Choose a new address for the kernel, for now we'll hard
>> + * code the destination.
>> + */
>> +static inline void __init *determine_relocation_address(void)
>> +{
>> +    return (void *)(CACHE_BASE + 0x02000000);
>> +}
>> +
>> +static inline int __init relocation_addr_valid(void *loc_new)
>> +{
>> +    if ((unsigned long)loc_new & 0x0000ffff) {
>
> Hi, Youling,
>
>
> 12bits-aligned is OK as actually R_LARCH_PCALA_LO12 is absolute.

Yes, 12bits-aligned is enough.

But for the convenience of debugging, is __kaslr_offset more friendly
to align with 1M? (For example, use objdump -d vmlinux --start-address=
(real_addr - __kaslr_offset)).

>
>
> BTW, I think the relocation of kernel looks like the '.so' solve its
> Relocs at user space so that it can be placed any legal address. The
> address is determined first, and relocation make it works on that address.
> Thus, this patch always relocate kernel to 'CACHE_BASE + 0x02000000'
> makes me puzzled. I think the relocation only works when the kernel
> runtime address is different from the link-time address.

IMHO, an immutable offset (eg: 0x1e00000) for the relocation kernel may
not make much sense, it may only be used during debugging to confirm
whether the relocation kernel offset is as expected. (We can remove the
immutable offset code if you think it is unnecessary) A random offset
will be generated when KASLR is enabled.

Thanks,
Youling

>
>
> Thanks,
> Jinyang
>
>
>> +        /* Inappropriately aligned new location */
>> +        return 0;
>> +    }
>> +    if ((unsigned long)loc_new < (unsigned long)_end) {
>> +        /* New location overlaps original kernel */
>> +        return 0;
>> +    }
>> +    return 1;
>> +}
>> +
>> +void *__init relocate_kernel(void)
>> +{
>> +    Elf64_Rela *rela, *rela_end;
>> +    void *loc_new;
>> +    unsigned long kernel_length;
>> +    long offset = 0;
>> +    int res = 1;
>> +    /* Default to original kernel entry point */
>> +    void *kernel_entry = start_kernel;
>> +
>> +    kernel_length = (long)(_end) - (long)(_text);
>> +
>> +    loc_new = determine_relocation_address();
>> +
>> +    /* Sanity check relocation address */
>> +    if (relocation_addr_valid(loc_new))
>> +        offset = (unsigned long)loc_new - (unsigned long)(_text);
>> +
>> +    if (offset) {
>> +        /* Copy the kernel to it's new location */
>> +        memcpy(loc_new, _text, kernel_length);
>> +
>> +        /* Sync the caches ready for execution of new kernel */
>> +        __asm__ __volatile__ (
>> +            "ibar 0 \t\n"
>> +            "dbar 0 \t\n");
>> +
>> +        rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
>> +        rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
>> +
>> +        for ( ; rela < rela_end; rela++) {
>> +            Elf64_Addr addr = rela->r_offset;
>> +            Elf64_Addr relocated_addr = rela->r_addend;
>> +
>> +            if (rela->r_info != R_LARCH_RELATIVE)
>> +                continue;
>> +
>> +            if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
>> +                relocated_addr = RELOCATED(relocated_addr);
>> +
>> +            *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
>> +
>> +        }
>> +
>> +        /* The current thread is now within the relocated image */
>> +        __current_thread_info = RELOCATED(__current_thread_info);
>> +
>> +        /* Return the new kernel's entry point */
>> +        kernel_entry = RELOCATED(start_kernel);
>> +    }
>> +out:
>> +    return kernel_entry;
>> +}
>> diff --git a/arch/loongarch/kernel/vmlinux.lds.S
>> b/arch/loongarch/kernel/vmlinux.lds.S
>> index 733b16e8d55d..aec0b6567d24 100644
>> --- a/arch/loongarch/kernel/vmlinux.lds.S
>> +++ b/arch/loongarch/kernel/vmlinux.lds.S
>> @@ -70,6 +70,8 @@ SECTIONS
>>       .plt : ALIGN(16) { *(.plt) }
>>       .got.plt : ALIGN(16) { *(.got.plt) }
>>   +    .data.rel : { *(.data.rel*) }
>> +
>>       . = ALIGN(PECOFF_SEGMENT_ALIGN);
>>       __init_begin = .;
>>       __inittext_begin = .;
>> @@ -93,8 +95,6 @@ SECTIONS
>>       PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
>>   #endif
>>   -    .rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
>> -
>>       .init.bss : {
>>           *(.init.bss)
>>       }
>> @@ -107,6 +107,12 @@ SECTIONS
>>       RO_DATA(4096)
>>       RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
>>   +    .rela.dyn : ALIGN(8) {
>> +        __rela_dyn_start = .;
>> +         *(.rela.dyn) *(.rela*)
>> +        __rela_dyn_end = .;
>> +    }
>> +
>>       .sdata : {
>>           *(.sdata)
>>       }
>> @@ -133,6 +139,7 @@ SECTIONS
>>         DISCARDS
>>       /DISCARD/ : {
>> +        *(.dynamic .dynsym .dynstr .hash .gnu.hash)
>>           *(.gnu.attributes)
>>           *(.options)
>>           *(.eh_frame)
  

On 2023-01-14 15:50, Youling Tang wrote:
> Hi, Jinyang
>
> On 01/14/2023 02:54 PM, Jinyang He wrote:
>>
>> On 2023-01-09 17:07, Youling Tang wrote:
>>> arch/loongarch/kernel/relocate.c contains the functions necessary to
>>> relocate the kernel elsewhere in memory.
>>>
>>> The kernel makes a copy of itself at the new address. It uses the
>>> relocation table inserted by the relocs tool to fix symbol references
>>> within the new image.
>>>
>>> If copy/relocation is successful then the entry point of the new kernel
>>> is returned, otherwise fall back to starting the kernel in place.
>>>
>>> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
>>> ---
>>>   arch/loongarch/Kconfig              | 15 +++++
>>>   arch/loongarch/Makefile             |  5 ++
>>>   arch/loongarch/kernel/Makefile      |  2 +
>>>   arch/loongarch/kernel/head.S        | 18 ++++++
>>>   arch/loongarch/kernel/relocate.c    | 96 
>>> +++++++++++++++++++++++++++++
>>>   arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>>>   6 files changed, 145 insertions(+), 2 deletions(-)
>>>   create mode 100644 arch/loongarch/kernel/relocate.c
>>>
>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>> index 9cc8b84f7eb0..089a4695b1b3 100644
>>> --- a/arch/loongarch/Kconfig
>>> +++ b/arch/loongarch/Kconfig
>>> @@ -48,6 +48,7 @@ config LOONGARCH
>>>       select ARCH_SUPPORTS_ATOMIC_RMW
>>>       select ARCH_SUPPORTS_HUGETLBFS
>>>       select ARCH_SUPPORTS_NUMA_BALANCING
>>> +    select SYS_SUPPORTS_RELOCATABLE
>>>       select ARCH_USE_BUILTIN_BSWAP
>>>       select ARCH_USE_CMPXCHG_LOCKREF
>>>       select ARCH_USE_QUEUED_RWLOCKS
>>> @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER
>>>   config AS_HAS_EXPLICIT_RELOCS
>>>       def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
>>>   +config SYS_SUPPORTS_RELOCATABLE
>>> +    bool
>>> +    help
>>> +      Selected if the platform supports relocating the kernel.
>>> +
>>>   menu "Kernel type and options"
>>>     source "kernel/Kconfig.hz"
>>> @@ -474,6 +480,15 @@ config PHYSICAL_START
>>>         specified in the "crashkernel=YM@XM" command line boot 
>>> parameter
>>>         passed to the panic-ed kernel).
>>>   +config RELOCATABLE
>>> +    bool "Relocatable kernel"
>>> +    depends on SYS_SUPPORTS_RELOCATABLE
>>> +    help
>>> +      This builds the kernel as a Position Independent Executable 
>>> (PIE),
>>> +      which retains all relocation metadata required to relocate the
>>> +      kernel binary at runtime to a different virtual address than the
>>> +      address it was linked at.
>>> +
>>>   config SECCOMP
>>>       bool "Enable seccomp to safely compute untrusted bytecode"
>>>       depends on PROC_FS
>>> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
>>> index 4402387d2755..27b5a70ff31c 100644
>>> --- a/arch/loongarch/Makefile
>>> +++ b/arch/loongarch/Makefile
>>> @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE        +=
>>> -Wa,-mla-global-with-abs
>>>   KBUILD_CFLAGS_MODULE        += -fplt
>>> -Wa,-mla-global-with-abs,-mla-local-with-abs
>>>   endif
>>>   +ifeq ($(CONFIG_RELOCATABLE),y)
>>> +LDFLAGS_vmlinux            += -static -pie --no-dynamic-linker -z 
>>> notext
>>> +KBUILD_CFLAGS_KERNEL        += -fPIE
>>> +endif
>>> +
>>>   cflags-y += -ffreestanding
>>>   cflags-y += $(call cc-option, -mno-check-zero-division)
>>>   diff --git a/arch/loongarch/kernel/Makefile
>>> b/arch/loongarch/kernel/Makefile
>>> index fcaa024a685e..33787d22e6f4 100644
>>> --- a/arch/loongarch/kernel/Makefile
>>> +++ b/arch/loongarch/kernel/Makefile
>>> @@ -31,6 +31,8 @@ endif
>>>   obj-$(CONFIG_MODULES)        += module.o module-sections.o
>>>   obj-$(CONFIG_STACKTRACE)    += stacktrace.o
>>>   +obj-$(CONFIG_RELOCATABLE)    += relocate.o
>>> +
>>>   obj-$(CONFIG_PROC_FS)        += proc.o
>>>     obj-$(CONFIG_SMP)        += smp.o
>>> diff --git a/arch/loongarch/kernel/head.S 
>>> b/arch/loongarch/kernel/head.S
>>> index e8a4bf9d7599..6db1549177ad 100644
>>> --- a/arch/loongarch/kernel/head.S
>>> +++ b/arch/loongarch/kernel/head.S
>>> @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry)            # kernel
>>> entry point
>>>       PTR_ADD        sp, sp, tp
>>>       set_saved_sp    sp, t0, t1
>>>   +#ifdef CONFIG_RELOCATABLE
>>> +    /* Copy kernel and apply the relocations */
>>> +    bl        relocate_kernel
>>> +
>>> +    /* Repoint the sp into the new kernel image */
>>> +    PTR_LI        sp, (_THREAD_SIZE - 32 - PT_SIZE)
>>> +    PTR_ADD        sp, sp, tp
>>> +    set_saved_sp    sp, t0, t1
>>> +    PTR_ADDI    sp, sp, -4 * SZREG      # init stack pointer
>>> +
>>> +    /*
>>> +     * relocate_kernel returns the entry point either
>>> +     * in the relocated kernel or the original if for
>>> +     * some reason relocation failed.
>>> +    */
>>> +    jr        a0
>>> +#else
>>>       bl        start_kernel
>>> +#endif
>>>       ASM_BUG()
>>>     SYM_CODE_END(kernel_entry)
>>> diff --git a/arch/loongarch/kernel/relocate.c
>>> b/arch/loongarch/kernel/relocate.c
>>> new file mode 100644
>>> index 000000000000..a58551c0698d
>>> --- /dev/null
>>> +++ b/arch/loongarch/kernel/relocate.c
>>> @@ -0,0 +1,96 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Support for Kernel relocation at boot time
>>> + *
>>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>>> + */
>>> +
>>> +#include <linux/elf.h>
>>> +#include <linux/kernel.h>
>>> +#include <linux/start_kernel.h>
>>> +#include <linux/printk.h>
>>> +#include <linux/panic_notifier.h>
>>> +#include <asm/bootinfo.h>
>>> +#include <asm/inst.h>
>>> +#include <asm/sections.h>
>>> +
>>> +#define RELOCATED(x) ((void *)((long)x + offset))
>>> +
>>> +extern long __rela_dyn_start;
>>> +extern long __rela_dyn_end;
>>> +
>>> +/*
>>> + * Choose a new address for the kernel, for now we'll hard
>>> + * code the destination.
>>> + */
>>> +static inline void __init *determine_relocation_address(void)
>>> +{
>>> +    return (void *)(CACHE_BASE + 0x02000000);
>>> +}
>>> +
>>> +static inline int __init relocation_addr_valid(void *loc_new)
>>> +{
>>> +    if ((unsigned long)loc_new & 0x0000ffff) {
>>
>> Hi, Youling,
>>
>>
>> 12bits-aligned is OK as actually R_LARCH_PCALA_LO12 is absolute.
>
> Yes, 12bits-aligned is enough.
>
> But for the convenience of debugging, is __kaslr_offset more friendly
> to align with 1M? (For example, use objdump -d vmlinux --start-address=
> (real_addr - __kaslr_offset)).

This will reduce the random range, but it's up to you.


>
>>
>>
>> BTW, I think the relocation of kernel looks like the '.so' solve its
>> Relocs at user space so that it can be placed any legal address. The
>> address is determined first, and relocation make it works on that 
>> address.
>> Thus, this patch always relocate kernel to 'CACHE_BASE + 0x02000000'
>> makes me puzzled. I think the relocation only works when the kernel
>> runtime address is different from the link-time address.
>
> IMHO, an immutable offset (eg: 0x1e00000) for the relocation kernel may
> not make much sense, it may only be used during debugging to confirm
> whether the relocation kernel offset is as expected. (We can remove the
> immutable offset code if you think it is unnecessary) A random offset
> will be generated when KASLR is enabled.

What I expected is that when the kernel runtime address is different
from the link-time address, the relocatable kernel can solve its
Relocs so that it can work well again. And the immutable offset is
relocate kernel to another address, that looks like one of random
offsets. Although relocatable and kaslr are similar, they are not the same.


Thanks,

Jinyang


>
> Thanks,
> Youling
>
>>
>>
>> Thanks,
>> Jinyang
>>
>>
>>> +        /* Inappropriately aligned new location */
>>> +        return 0;
>>> +    }
>>> +    if ((unsigned long)loc_new < (unsigned long)_end) {
>>> +        /* New location overlaps original kernel */
>>> +        return 0;
>>> +    }
>>> +    return 1;
>>> +}
>>> +
>>> +void *__init relocate_kernel(void)
>>> +{
>>> +    Elf64_Rela *rela, *rela_end;
>>> +    void *loc_new;
>>> +    unsigned long kernel_length;
>>> +    long offset = 0;
>>> +    int res = 1;
>>> +    /* Default to original kernel entry point */
>>> +    void *kernel_entry = start_kernel;
>>> +
>>> +    kernel_length = (long)(_end) - (long)(_text);
>>> +
>>> +    loc_new = determine_relocation_address();
>>> +
>>> +    /* Sanity check relocation address */
>>> +    if (relocation_addr_valid(loc_new))
>>> +        offset = (unsigned long)loc_new - (unsigned long)(_text);
>>> +
>>> +    if (offset) {
>>> +        /* Copy the kernel to it's new location */
>>> +        memcpy(loc_new, _text, kernel_length);
>>> +
>>> +        /* Sync the caches ready for execution of new kernel */
>>> +        __asm__ __volatile__ (
>>> +            "ibar 0 \t\n"
>>> +            "dbar 0 \t\n");
>>> +
>>> +        rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
>>> +        rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
>>> +
>>> +        for ( ; rela < rela_end; rela++) {
>>> +            Elf64_Addr addr = rela->r_offset;
>>> +            Elf64_Addr relocated_addr = rela->r_addend;
>>> +
>>> +            if (rela->r_info != R_LARCH_RELATIVE)
>>> +                continue;
>>> +
>>> +            if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
>>> +                relocated_addr = RELOCATED(relocated_addr);
>>> +
>>> +            *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
>>> +
>>> +        }
>>> +
>>> +        /* The current thread is now within the relocated image */
>>> +        __current_thread_info = RELOCATED(__current_thread_info);
>>> +
>>> +        /* Return the new kernel's entry point */
>>> +        kernel_entry = RELOCATED(start_kernel);
>>> +    }
>>> +out:
>>> +    return kernel_entry;
>>> +}
>>> diff --git a/arch/loongarch/kernel/vmlinux.lds.S
>>> b/arch/loongarch/kernel/vmlinux.lds.S
>>> index 733b16e8d55d..aec0b6567d24 100644
>>> --- a/arch/loongarch/kernel/vmlinux.lds.S
>>> +++ b/arch/loongarch/kernel/vmlinux.lds.S
>>> @@ -70,6 +70,8 @@ SECTIONS
>>>       .plt : ALIGN(16) { *(.plt) }
>>>       .got.plt : ALIGN(16) { *(.got.plt) }
>>>   +    .data.rel : { *(.data.rel*) }
>>> +
>>>       . = ALIGN(PECOFF_SEGMENT_ALIGN);
>>>       __init_begin = .;
>>>       __inittext_begin = .;
>>> @@ -93,8 +95,6 @@ SECTIONS
>>>       PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
>>>   #endif
>>>   -    .rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
>>> -
>>>       .init.bss : {
>>>           *(.init.bss)
>>>       }
>>> @@ -107,6 +107,12 @@ SECTIONS
>>>       RO_DATA(4096)
>>>       RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
>>>   +    .rela.dyn : ALIGN(8) {
>>> +        __rela_dyn_start = .;
>>> +         *(.rela.dyn) *(.rela*)
>>> +        __rela_dyn_end = .;
>>> +    }
>>> +
>>>       .sdata : {
>>>           *(.sdata)
>>>       }
>>> @@ -133,6 +139,7 @@ SECTIONS
>>>         DISCARDS
>>>       /DISCARD/ : {
>>> +        *(.dynamic .dynsym .dynstr .hash .gnu.hash)
>>>           *(.gnu.attributes)
>>>           *(.options)
>>>           *(.eh_frame)
>
  

On 01/14/2023 04:30 PM, Jinyang He wrote:
>
> On 2023-01-14 15:50, Youling Tang wrote:
>> Hi, Jinyang
>>
>> On 01/14/2023 02:54 PM, Jinyang He wrote:
>>>
>>> On 2023-01-09 17:07, Youling Tang wrote:
>>>> arch/loongarch/kernel/relocate.c contains the functions necessary to
>>>> relocate the kernel elsewhere in memory.
>>>>
>>>> The kernel makes a copy of itself at the new address. It uses the
>>>> relocation table inserted by the relocs tool to fix symbol references
>>>> within the new image.
>>>>
>>>> If copy/relocation is successful then the entry point of the new kernel
>>>> is returned, otherwise fall back to starting the kernel in place.
>>>>
>>>> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
>>>> ---
>>>>   arch/loongarch/Kconfig              | 15 +++++
>>>>   arch/loongarch/Makefile             |  5 ++
>>>>   arch/loongarch/kernel/Makefile      |  2 +
>>>>   arch/loongarch/kernel/head.S        | 18 ++++++
>>>>   arch/loongarch/kernel/relocate.c    | 96
>>>> +++++++++++++++++++++++++++++
>>>>   arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>>>>   6 files changed, 145 insertions(+), 2 deletions(-)
>>>>   create mode 100644 arch/loongarch/kernel/relocate.c
>>>>
>>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>>> index 9cc8b84f7eb0..089a4695b1b3 100644
>>>> --- a/arch/loongarch/Kconfig
>>>> +++ b/arch/loongarch/Kconfig
>>>> @@ -48,6 +48,7 @@ config LOONGARCH
>>>>       select ARCH_SUPPORTS_ATOMIC_RMW
>>>>       select ARCH_SUPPORTS_HUGETLBFS
>>>>       select ARCH_SUPPORTS_NUMA_BALANCING
>>>> +    select SYS_SUPPORTS_RELOCATABLE
>>>>       select ARCH_USE_BUILTIN_BSWAP
>>>>       select ARCH_USE_CMPXCHG_LOCKREF
>>>>       select ARCH_USE_QUEUED_RWLOCKS
>>>> @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER
>>>>   config AS_HAS_EXPLICIT_RELOCS
>>>>       def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
>>>>   +config SYS_SUPPORTS_RELOCATABLE
>>>> +    bool
>>>> +    help
>>>> +      Selected if the platform supports relocating the kernel.
>>>> +
>>>>   menu "Kernel type and options"
>>>>     source "kernel/Kconfig.hz"
>>>> @@ -474,6 +480,15 @@ config PHYSICAL_START
>>>>         specified in the "crashkernel=YM@XM" command line boot
>>>> parameter
>>>>         passed to the panic-ed kernel).
>>>>   +config RELOCATABLE
>>>> +    bool "Relocatable kernel"
>>>> +    depends on SYS_SUPPORTS_RELOCATABLE
>>>> +    help
>>>> +      This builds the kernel as a Position Independent Executable
>>>> (PIE),
>>>> +      which retains all relocation metadata required to relocate the
>>>> +      kernel binary at runtime to a different virtual address than the
>>>> +      address it was linked at.
>>>> +
>>>>   config SECCOMP
>>>>       bool "Enable seccomp to safely compute untrusted bytecode"
>>>>       depends on PROC_FS
>>>> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
>>>> index 4402387d2755..27b5a70ff31c 100644
>>>> --- a/arch/loongarch/Makefile
>>>> +++ b/arch/loongarch/Makefile
>>>> @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE        +=
>>>> -Wa,-mla-global-with-abs
>>>>   KBUILD_CFLAGS_MODULE        += -fplt
>>>> -Wa,-mla-global-with-abs,-mla-local-with-abs
>>>>   endif
>>>>   +ifeq ($(CONFIG_RELOCATABLE),y)
>>>> +LDFLAGS_vmlinux            += -static -pie --no-dynamic-linker -z
>>>> notext
>>>> +KBUILD_CFLAGS_KERNEL        += -fPIE
>>>> +endif
>>>> +
>>>>   cflags-y += -ffreestanding
>>>>   cflags-y += $(call cc-option, -mno-check-zero-division)
>>>>   diff --git a/arch/loongarch/kernel/Makefile
>>>> b/arch/loongarch/kernel/Makefile
>>>> index fcaa024a685e..33787d22e6f4 100644
>>>> --- a/arch/loongarch/kernel/Makefile
>>>> +++ b/arch/loongarch/kernel/Makefile
>>>> @@ -31,6 +31,8 @@ endif
>>>>   obj-$(CONFIG_MODULES)        += module.o module-sections.o
>>>>   obj-$(CONFIG_STACKTRACE)    += stacktrace.o
>>>>   +obj-$(CONFIG_RELOCATABLE)    += relocate.o
>>>> +
>>>>   obj-$(CONFIG_PROC_FS)        += proc.o
>>>>     obj-$(CONFIG_SMP)        += smp.o
>>>> diff --git a/arch/loongarch/kernel/head.S
>>>> b/arch/loongarch/kernel/head.S
>>>> index e8a4bf9d7599..6db1549177ad 100644
>>>> --- a/arch/loongarch/kernel/head.S
>>>> +++ b/arch/loongarch/kernel/head.S
>>>> @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry)            # kernel
>>>> entry point
>>>>       PTR_ADD        sp, sp, tp
>>>>       set_saved_sp    sp, t0, t1
>>>>   +#ifdef CONFIG_RELOCATABLE
>>>> +    /* Copy kernel and apply the relocations */
>>>> +    bl        relocate_kernel
>>>> +
>>>> +    /* Repoint the sp into the new kernel image */
>>>> +    PTR_LI        sp, (_THREAD_SIZE - 32 - PT_SIZE)
>>>> +    PTR_ADD        sp, sp, tp
>>>> +    set_saved_sp    sp, t0, t1
>>>> +    PTR_ADDI    sp, sp, -4 * SZREG      # init stack pointer
>>>> +
>>>> +    /*
>>>> +     * relocate_kernel returns the entry point either
>>>> +     * in the relocated kernel or the original if for
>>>> +     * some reason relocation failed.
>>>> +    */
>>>> +    jr        a0
>>>> +#else
>>>>       bl        start_kernel
>>>> +#endif
>>>>       ASM_BUG()
>>>>     SYM_CODE_END(kernel_entry)
>>>> diff --git a/arch/loongarch/kernel/relocate.c
>>>> b/arch/loongarch/kernel/relocate.c
>>>> new file mode 100644
>>>> index 000000000000..a58551c0698d
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/relocate.c
>>>> @@ -0,0 +1,96 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Support for Kernel relocation at boot time
>>>> + *
>>>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#include <linux/elf.h>
>>>> +#include <linux/kernel.h>
>>>> +#include <linux/start_kernel.h>
>>>> +#include <linux/printk.h>
>>>> +#include <linux/panic_notifier.h>
>>>> +#include <asm/bootinfo.h>
>>>> +#include <asm/inst.h>
>>>> +#include <asm/sections.h>
>>>> +
>>>> +#define RELOCATED(x) ((void *)((long)x + offset))
>>>> +
>>>> +extern long __rela_dyn_start;
>>>> +extern long __rela_dyn_end;
>>>> +
>>>> +/*
>>>> + * Choose a new address for the kernel, for now we'll hard
>>>> + * code the destination.
>>>> + */
>>>> +static inline void __init *determine_relocation_address(void)
>>>> +{
>>>> +    return (void *)(CACHE_BASE + 0x02000000);
>>>> +}
>>>> +
>>>> +static inline int __init relocation_addr_valid(void *loc_new)
>>>> +{
>>>> +    if ((unsigned long)loc_new & 0x0000ffff) {
>>>
>>> Hi, Youling,
>>>
>>>
>>> 12bits-aligned is OK as actually R_LARCH_PCALA_LO12 is absolute.
>>
>> Yes, 12bits-aligned is enough.
>>
>> But for the convenience of debugging, is __kaslr_offset more friendly
>> to align with 1M? (For example, use objdump -d vmlinux --start-address=
>> (real_addr - __kaslr_offset)).
>
> This will reduce the random range, but it's up to you.
>
>
>>
>>>
>>>
>>> BTW, I think the relocation of kernel looks like the '.so' solve its
>>> Relocs at user space so that it can be placed any legal address. The
>>> address is determined first, and relocation make it works on that
>>> address.
>>> Thus, this patch always relocate kernel to 'CACHE_BASE + 0x02000000'
>>> makes me puzzled. I think the relocation only works when the kernel
>>> runtime address is different from the link-time address.
>>
>> IMHO, an immutable offset (eg: 0x1e00000) for the relocation kernel may
>> not make much sense, it may only be used during debugging to confirm
>> whether the relocation kernel offset is as expected. (We can remove the
>> immutable offset code if you think it is unnecessary) A random offset
>> will be generated when KASLR is enabled.
>
> What I expected is that when the kernel runtime address is different
> from the link-time address, the relocatable kernel can solve its
> Relocs so that it can work well again. And the immutable offset is
> relocate kernel to another address, that looks like one of random
> offsets. Although relocatable and kaslr are similar, they are not the same.

Yes, this solution is better. The kernel can perform adaptive
operations (for example, the same set of binary features of kdump to be
implemented later).

At present, the existing implementation scheme may be used. When the
same set of binary features of kdump is implemented later, this new
scheme can be used to improve the implementation of the relocation
kernel.

Thanks,
Youling

>
>
> Thanks,
>
> Jinyang
>
>
>>
>> Thanks,
>> Youling
>>
>>>
>>>
>>> Thanks,
>>> Jinyang
>>>
>>>
>>>> +        /* Inappropriately aligned new location */
>>>> +        return 0;
>>>> +    }
>>>> +    if ((unsigned long)loc_new < (unsigned long)_end) {
>>>> +        /* New location overlaps original kernel */
>>>> +        return 0;
>>>> +    }
>>>> +    return 1;
>>>> +}
>>>> +
>>>> +void *__init relocate_kernel(void)
>>>> +{
>>>> +    Elf64_Rela *rela, *rela_end;
>>>> +    void *loc_new;
>>>> +    unsigned long kernel_length;
>>>> +    long offset = 0;
>>>> +    int res = 1;
>>>> +    /* Default to original kernel entry point */
>>>> +    void *kernel_entry = start_kernel;
>>>> +
>>>> +    kernel_length = (long)(_end) - (long)(_text);
>>>> +
>>>> +    loc_new = determine_relocation_address();
>>>> +
>>>> +    /* Sanity check relocation address */
>>>> +    if (relocation_addr_valid(loc_new))
>>>> +        offset = (unsigned long)loc_new - (unsigned long)(_text);
>>>> +
>>>> +    if (offset) {
>>>> +        /* Copy the kernel to it's new location */
>>>> +        memcpy(loc_new, _text, kernel_length);
>>>> +
>>>> +        /* Sync the caches ready for execution of new kernel */
>>>> +        __asm__ __volatile__ (
>>>> +            "ibar 0 \t\n"
>>>> +            "dbar 0 \t\n");
>>>> +
>>>> +        rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start);
>>>> +        rela_end = (Elf64_Rela *)RELOCATED(&__rela_dyn_end);
>>>> +
>>>> +        for ( ; rela < rela_end; rela++) {
>>>> +            Elf64_Addr addr = rela->r_offset;
>>>> +            Elf64_Addr relocated_addr = rela->r_addend;
>>>> +
>>>> +            if (rela->r_info != R_LARCH_RELATIVE)
>>>> +                continue;
>>>> +
>>>> +            if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
>>>> +                relocated_addr = RELOCATED(relocated_addr);
>>>> +
>>>> +            *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
>>>> +
>>>> +        }
>>>> +
>>>> +        /* The current thread is now within the relocated image */
>>>> +        __current_thread_info = RELOCATED(__current_thread_info);
>>>> +
>>>> +        /* Return the new kernel's entry point */
>>>> +        kernel_entry = RELOCATED(start_kernel);
>>>> +    }
>>>> +out:
>>>> +    return kernel_entry;
>>>> +}
>>>> diff --git a/arch/loongarch/kernel/vmlinux.lds.S
>>>> b/arch/loongarch/kernel/vmlinux.lds.S
>>>> index 733b16e8d55d..aec0b6567d24 100644
>>>> --- a/arch/loongarch/kernel/vmlinux.lds.S
>>>> +++ b/arch/loongarch/kernel/vmlinux.lds.S
>>>> @@ -70,6 +70,8 @@ SECTIONS
>>>>       .plt : ALIGN(16) { *(.plt) }
>>>>       .got.plt : ALIGN(16) { *(.got.plt) }
>>>>   +    .data.rel : { *(.data.rel*) }
>>>> +
>>>>       . = ALIGN(PECOFF_SEGMENT_ALIGN);
>>>>       __init_begin = .;
>>>>       __inittext_begin = .;
>>>> @@ -93,8 +95,6 @@ SECTIONS
>>>>       PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT)
>>>>   #endif
>>>>   -    .rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
>>>> -
>>>>       .init.bss : {
>>>>           *(.init.bss)
>>>>       }
>>>> @@ -107,6 +107,12 @@ SECTIONS
>>>>       RO_DATA(4096)
>>>>       RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE)
>>>>   +    .rela.dyn : ALIGN(8) {
>>>> +        __rela_dyn_start = .;
>>>> +         *(.rela.dyn) *(.rela*)
>>>> +        __rela_dyn_end = .;
>>>> +    }
>>>> +
>>>>       .sdata : {
>>>>           *(.sdata)
>>>>       }
>>>> @@ -133,6 +139,7 @@ SECTIONS
>>>>         DISCARDS
>>>>       /DISCARD/ : {
>>>> +        *(.dynamic .dynsym .dynstr .hash .gnu.hash)
>>>>           *(.gnu.attributes)
>>>>           *(.options)
>>>>           *(.eh_frame)
>>
>