[v4,4/5] LoongArch: Add support for kernel relocation
Commit Message
This config allows to compile kernel as PIE and to relocate it at
any virtual address at runtime: this paves the way to KASLR.
Runtime relocation is possible since relocation metadata are embedded
into the kernel.
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Xi Ruoyao <xry111@xry111.site> # Use arch_initcall
---
arch/loongarch/Kconfig | 15 ++++++
arch/loongarch/Makefile | 5 ++
arch/loongarch/kernel/Makefile | 2 +
arch/loongarch/kernel/head.S | 5 ++
arch/loongarch/kernel/relocate.c | 78 +++++++++++++++++++++++++++++
arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
6 files changed, 114 insertions(+), 2 deletions(-)
create mode 100644 arch/loongarch/kernel/relocate.c
Comments
Hi, Youling,
On Fri, Feb 10, 2023 at 4:48 PM Youling Tang <tangyouling@loongson.cn> wrote:
>
> This config allows to compile kernel as PIE and to relocate it at
> any virtual address at runtime: this paves the way to KASLR.
> Runtime relocation is possible since relocation metadata are embedded
> into the kernel.
>
> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
> Signed-off-by: Xi Ruoyao <xry111@xry111.site> # Use arch_initcall
> ---
> arch/loongarch/Kconfig | 15 ++++++
> arch/loongarch/Makefile | 5 ++
> arch/loongarch/kernel/Makefile | 2 +
> arch/loongarch/kernel/head.S | 5 ++
> arch/loongarch/kernel/relocate.c | 78 +++++++++++++++++++++++++++++
> arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
> 6 files changed, 114 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
We don't need such a Kconfig option since it is always true.
Huacai
> 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 += $(call cc-option, -mno-check-zero-division)
>
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index c8cfbd562921..3341dd5f0926 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -31,6 +31,8 @@ endif
> obj-$(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 d2ac26b5b22b..499edc80d8ab 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -86,6 +86,11 @@ SYM_CODE_START(kernel_entry) # kernel entry point
> PTR_ADD sp, sp, tp
> set_saved_sp sp, t0, t1
>
> +#ifdef CONFIG_RELOCATABLE
> + /* Apply the relocations */
> + bl relocate_kernel
> +#endif
> +
> bl start_kernel
> ASM_BUG()
>
> diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
> new file mode 100644
> index 000000000000..91ce92433bab
> --- /dev/null
> +++ b/arch/loongarch/kernel/relocate.c
> @@ -0,0 +1,78 @@
> +// 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/printk.h>
> +#include <linux/panic_notifier.h>
> +#include <asm/sections.h>
> +
> +#define RELOCATED(x) ((void *)((long)x + reloc_offset))
> +
> +extern long __rela_dyn_start;
> +extern long __rela_dyn_end;
> +
> +static unsigned long reloc_offset;
> +
> +void __init relocate_kernel(void)
> +{
> + reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
> +
> + if (reloc_offset) {
> + Elf64_Rela *rela, *rela_end;
> + rela = (Elf64_Rela *)&__rela_dyn_start;
> + rela_end = (Elf64_Rela *)&__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 =
> + (Elf64_Addr)RELOCATED(relocated_addr);
> +
> + *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
> + }
> + }
> +}
> +
> +/*
> + * Show relocation information on panic.
> + */
> +static void show_kernel_relocation(const char *level)
> +{
> + if (reloc_offset > 0) {
> + printk(level);
> + pr_cont("Kernel relocated offset @ 0x%lx\n", reloc_offset);
> + pr_cont(" .text @ 0x%lx\n", (unsigned long)&_text);
> + pr_cont(" .data @ 0x%lx\n", (unsigned long)&_sdata);
> + pr_cont(" .bss @ 0x%lx\n", (unsigned long)&__bss_start);
> + }
> +}
> +
> +static int kernel_location_notifier_fn(struct notifier_block *self,
> + unsigned long v, void *p)
> +{
> + show_kernel_relocation(KERN_EMERG);
> + return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block kernel_location_notifier = {
> + .notifier_call = kernel_location_notifier_fn
> +};
> +
> +static int __init register_kernel_offset_dumper(void)
> +{
> + atomic_notifier_chain_register(&panic_notifier_list,
> + &kernel_location_notifier);
> + return 0;
> +}
> +
> +arch_initcall(register_kernel_offset_dumper);
> 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)
> --
> 2.37.3
>
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-rc7 next-20230210]
[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-la-pcrel-instead-of-la-abs-when-it-s-trivially-possible/20230210-165022
patch link: https://lore.kernel.org/r/1676018856-26520-5-git-send-email-tangyouling%40loongson.cn
patch subject: [PATCH v4 4/5] LoongArch: Add support for kernel relocation
config: loongarch-allmodconfig (https://download.01.org/0day-ci/archive/20230211/202302110150.tIuRIiTp-lkp@intel.com/config)
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/26dc7750408c7f232632db44fab905df7b48d83c
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Youling-Tang/LoongArch-Use-la-pcrel-instead-of-la-abs-when-it-s-trivially-possible/20230210-165022
git checkout 26dc7750408c7f232632db44fab905df7b48d83c
# 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>
| Link: https://lore.kernel.org/oe-kbuild-all/202302110150.tIuRIiTp-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:21:13: warning: no previous prototype for 'relocate_kernel' [-Wmissing-prototypes]
21 | void __init relocate_kernel(void)
| ^~~~~~~~~~~~~~~
vim +/relocate_kernel +21 arch/loongarch/kernel/relocate.c
20
> 21 void __init relocate_kernel(void)
22 {
23 reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
24
25 if (reloc_offset) {
26 Elf64_Rela *rela, *rela_end;
27 rela = (Elf64_Rela *)&__rela_dyn_start;
28 rela_end = (Elf64_Rela *)&__rela_dyn_end;
29
30 for ( ; rela < rela_end; rela++) {
31 Elf64_Addr addr = rela->r_offset;
32 Elf64_Addr relocated_addr = rela->r_addend;
33
34 if (rela->r_info != R_LARCH_RELATIVE)
35 continue;
36
37 if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
38 relocated_addr =
39 (Elf64_Addr)RELOCATED(relocated_addr);
40
41 *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
42 }
43 }
44 }
45
@@ -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
@@ -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 += $(call cc-option, -mno-check-zero-division)
@@ -31,6 +31,8 @@ endif
obj-$(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
@@ -86,6 +86,11 @@ SYM_CODE_START(kernel_entry) # kernel entry point
PTR_ADD sp, sp, tp
set_saved_sp sp, t0, t1
+#ifdef CONFIG_RELOCATABLE
+ /* Apply the relocations */
+ bl relocate_kernel
+#endif
+
bl start_kernel
ASM_BUG()
new file mode 100644
@@ -0,0 +1,78 @@
+// 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/printk.h>
+#include <linux/panic_notifier.h>
+#include <asm/sections.h>
+
+#define RELOCATED(x) ((void *)((long)x + reloc_offset))
+
+extern long __rela_dyn_start;
+extern long __rela_dyn_end;
+
+static unsigned long reloc_offset;
+
+void __init relocate_kernel(void)
+{
+ reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
+
+ if (reloc_offset) {
+ Elf64_Rela *rela, *rela_end;
+ rela = (Elf64_Rela *)&__rela_dyn_start;
+ rela_end = (Elf64_Rela *)&__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 =
+ (Elf64_Addr)RELOCATED(relocated_addr);
+
+ *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
+ }
+ }
+}
+
+/*
+ * Show relocation information on panic.
+ */
+static void show_kernel_relocation(const char *level)
+{
+ if (reloc_offset > 0) {
+ printk(level);
+ pr_cont("Kernel relocated offset @ 0x%lx\n", reloc_offset);
+ pr_cont(" .text @ 0x%lx\n", (unsigned long)&_text);
+ pr_cont(" .data @ 0x%lx\n", (unsigned long)&_sdata);
+ pr_cont(" .bss @ 0x%lx\n", (unsigned long)&__bss_start);
+ }
+}
+
+static int kernel_location_notifier_fn(struct notifier_block *self,
+ unsigned long v, void *p)
+{
+ show_kernel_relocation(KERN_EMERG);
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block kernel_location_notifier = {
+ .notifier_call = kernel_location_notifier_fn
+};
+
+static int __init register_kernel_offset_dumper(void)
+{
+ atomic_notifier_chain_register(&panic_notifier_list,
+ &kernel_location_notifier);
+ return 0;
+}
+
+arch_initcall(register_kernel_offset_dumper);
@@ -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)