[PATCH v5 1/3] efi/loongarch: Randomize kernel preferred address for KASLR

[WANG Rui <r@hev.cc>]

Introduce efi_get_kimg_kaslr_address() helper to compute the preferred
kernel image load address dynamically when CONFIG_RANDOMIZE_BASE is
enabled. The function derives a random offset by using the EFI-provided
randomness combined with the timer tick value, and constrains it within
CONFIG_RANDOMIZE_BASE_MAX_OFFSET.

Update EFI_KIMG_PREFERRED_ADDRESS to call this helper so that the EFI
stub can select a randomized load address when KASLR is active, while
preserving the original base address behavior when KASLR is disabled or
"nokaslr" is specified.

Note: LoongArch can't KASLR for hibernation, so set efi_nokaslr to true
if "resume=<devname>" is explicitly specified in cmdline.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Co-authored-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: WANG Rui <r@hev.cc>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
 arch/loongarch/include/asm/efi.h               |  4 +++-
 drivers/firmware/efi/libstub/efi-stub-helper.c |  4 ++++
 drivers/firmware/efi/libstub/loongarch.c       | 16 ++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/efi.h b/arch/loongarch/include/asm/efi.h
index eddc8e79b3fa..1ad764b18c3e 100644
--- a/arch/loongarch/include/asm/efi.h
+++ b/arch/loongarch/include/asm/efi.h
@@ -30,6 +30,8 @@ static inline unsigned long efi_get_kimg_min_align(void)
 	return SZ_2M;
 }
 
-#define EFI_KIMG_PREFERRED_ADDRESS	PHYSADDR(VMLINUX_LOAD_ADDRESS)
+unsigned long efi_get_kimg_kaslr_address(void);
+
+#define EFI_KIMG_PREFERRED_ADDRESS efi_get_kimg_kaslr_address()
 
 #endif /* _ASM_LOONGARCH_EFI_H */
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 7aa2f9ad2935..f27f2e1f0019 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -79,6 +79,10 @@ efi_status_t efi_parse_options(char const *cmdline)
 			efi_noinitrd = true;
 		} else if (IS_ENABLED(CONFIG_X86_64) && !strcmp(param, "no5lvl")) {
 			efi_no5lvl = true;
+		} else if (IS_ENABLED(CONFIG_LOONGARCH) &&
+			   IS_ENABLED(CONFIG_HIBERNATION) &&
+			   !strcmp(param, "resume") && val) {
+			efi_nokaslr = true; /* LoongArch can't KASLR for hibernation */
 		} else if (IS_ENABLED(CONFIG_ARCH_HAS_MEM_ENCRYPT) &&
 			   !strcmp(param, "mem_encrypt") && val) {
 			if (parse_option_str(val, "on"))
diff --git a/drivers/firmware/efi/libstub/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
index f7938d5c196a..2b0c87dc9908 100644
--- a/drivers/firmware/efi/libstub/loongarch.c
+++ b/drivers/firmware/efi/libstub/loongarch.c
@@ -23,6 +23,22 @@ void efi_cache_sync_image(unsigned long image_base, unsigned long alloc_size)
 	asm volatile ("ibar 0" ::: "memory");
 }
 
+unsigned long efi_get_kimg_kaslr_address(void)
+{
+	unsigned int random_offset = 0;
+
+#ifdef CONFIG_RANDOMIZE_BASE
+	if (!efi_nokaslr) {
+		efi_get_random_bytes(sizeof(random_offset), (u8 *)&random_offset);
+		random_offset ^= (random_get_entropy() << 16);
+		random_offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
+		random_offset = ALIGN(random_offset + SZ_64K, SZ_64K);
+	}
+#endif
+
+	return PHYSADDR(VMLINUX_LOAD_ADDRESS) + random_offset;
+}
+
 struct exit_boot_struct {
 	efi_memory_desc_t	*runtime_map;
 	int			runtime_entry_count;
-- 
2.54.0