[4/4] LoongArch: Add support for kernel address space layout randomization (KASLR)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 089a4695b1b3..cdf0535764ae 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -489,6 +489,28 @@  config RELOCATABLE
 	  kernel binary at runtime to a different virtual address than the
 	  address it was linked at.
 
+config RANDOMIZE_BASE
+	bool "Randomize the address of the kernel image (KASLR)"
+	depends on RELOCATABLE
+	help
+	   Randomizes the physical and virtual address at which the
+	   kernel image is loaded, as a security feature that
+	   deters exploit attempts relying on knowledge of the location
+	   of kernel internals.
+
+	   The kernel will be offset by up to RANDOMIZE_BASE_MAX_OFFSET.
+
+	   If unsure, say N.
+
+config RANDOMIZE_BASE_MAX_OFFSET
+	hex "Maximum KASLR offset" if EXPERT
+	depends on RANDOMIZE_BASE
+	range 0x0 0x10000000 if 64BIT
+	default "0x01000000"
+	help
+	  When KASLR is active, this provides the maximum offset that will
+	  be applied to the kernel image.
+
 config SECCOMP
 	bool "Enable seccomp to safely compute untrusted bytecode"
 	depends on PROC_FS
diff --git a/arch/loongarch/include/asm/page.h b/arch/loongarch/include/asm/page.h
index 53f284a96182..6dda0d6271ca 100644
--- a/arch/loongarch/include/asm/page.h
+++ b/arch/loongarch/include/asm/page.h
@@ -106,6 +106,12 @@  extern int __virt_addr_valid(volatile void *kaddr);
 	 ((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0) | \
 	 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
 
+extern unsigned long __kaslr_offset;
+static inline unsigned long kaslr_offset(void)
+{
+	return __kaslr_offset;
+}
+
 #include <asm-generic/memory_model.h>
 #include <asm-generic/getorder.h>
 
diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
index a58551c0698d..b5070a015dd4 100644
--- a/arch/loongarch/kernel/relocate.c
+++ b/arch/loongarch/kernel/relocate.c
@@ -11,6 +11,7 @@ 
 #include <linux/printk.h>
 #include <linux/panic_notifier.h>
 #include <asm/bootinfo.h>
+#include <asm/early_ioremap.h>
 #include <asm/inst.h>
 #include <asm/sections.h>
 
@@ -19,6 +20,70 @@ 
 extern long __rela_dyn_start;
 extern long __rela_dyn_end;
 
+#ifdef CONFIG_RANDOMIZE_BASE
+
+static inline __init unsigned long rotate_xor(unsigned long hash,
+					      const void *area, size_t size)
+{
+	size_t i;
+	unsigned long *ptr = (unsigned long *)area;
+
+	for (i = 0; i < size / sizeof(hash); i++) {
+		/* Rotate by odd number of bits and XOR. */
+		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
+		hash ^= ptr[i];
+	}
+
+	return hash;
+}
+
+static inline __init unsigned long get_random_boot(void)
+{
+	unsigned long entropy = random_get_entropy();
+	unsigned long hash = 0;
+
+	/* Attempt to create a simple but unpredictable starting entropy. */
+	hash = rotate_xor(hash, linux_banner, strlen(linux_banner));
+
+	/* Add in any runtime entropy we can get */
+	hash = rotate_xor(hash, &entropy, sizeof(entropy));
+
+	return hash;
+}
+
+static inline __init bool kaslr_disabled(void)
+{
+	char *str;
+
+	str = strstr(boot_command_line, "nokaslr");
+	if (str == boot_command_line || (str > boot_command_line && *(str - 1) == ' '))
+		return true;
+
+	return false;
+}
+
+/* Choose a new address for the kernel */
+static inline void __init *determine_relocation_address(void)
+{
+	unsigned long kernel_length;
+	void *dest = _text;
+	unsigned long offset;
+
+	if (kaslr_disabled())
+		return dest;
+
+	kernel_length = (long)_end - (long)_text;
+
+	offset = get_random_boot() << 16;
+	offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
+	if (offset < kernel_length)
+		offset += ALIGN(kernel_length, 0xffff);
+
+	return RELOCATED(dest);
+}
+
+#else
+
 /*
  * Choose a new address for the kernel, for now we'll hard
  * code the destination.
@@ -28,6 +93,8 @@  static inline void __init *determine_relocation_address(void)
 	return (void *)(CACHE_BASE + 0x02000000);
 }
 
+#endif
+
 static inline int __init relocation_addr_valid(void *loc_new)
 {
 	if ((unsigned long)loc_new & 0x0000ffff) {
@@ -41,6 +108,13 @@  static inline int __init relocation_addr_valid(void *loc_new)
 	return 1;
 }
 
+static inline void __init update_kaslr_offset(unsigned long *addr, long offset)
+{
+	unsigned long *new_addr = (unsigned long *)RELOCATED(addr);
+
+	*new_addr = (unsigned long)offset;
+}
+
 void *__init relocate_kernel(void)
 {
 	Elf64_Rela *rela, *rela_end;
@@ -50,6 +124,10 @@  void *__init relocate_kernel(void)
 	int res = 1;
 	/* Default to original kernel entry point */
 	void *kernel_entry = start_kernel;
+	char *cmdline = early_ioremap(fw_arg1, COMMAND_LINE_SIZE);
+
+	/* Boot command line was passed in fw_arg1 */
+	strscpy(boot_command_line, cmdline, COMMAND_LINE_SIZE);
 
 	kernel_length = (long)(_end) - (long)(_text);
 
@@ -90,7 +168,43 @@  void *__init relocate_kernel(void)
 
 		/* Return the new kernel's entry point */
 		kernel_entry = RELOCATED(start_kernel);
+
+		/* Error may occur before, so keep it at last */
+		update_kaslr_offset(&__kaslr_offset, offset);
 	}
 out:
 	return kernel_entry;
 }
+
+/*
+ * Show relocation information on panic.
+ */
+static void show_kernel_relocation(const char *level)
+{
+	if (__kaslr_offset > 0) {
+		printk(level);
+		pr_cont("Kernel relocated offset @ 0x%lx\n", __kaslr_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;
+}
+__initcall(register_kernel_offset_dumper);
diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index 4344502c0b31..b2ba2741945c 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -82,6 +82,9 @@  static struct resource code_resource = { .name = "Kernel code", };
 static struct resource data_resource = { .name = "Kernel data", };
 static struct resource bss_resource  = { .name = "Kernel bss", };
 
+unsigned long __kaslr_offset __ro_after_init;
+EXPORT_SYMBOL(__kaslr_offset);
+
 const char *get_system_type(void)
 {
 	return "generic-loongson-machine";