[PATCH 2/3] efi/loongarch: Randomize kernel preferred address for KASLR

[WANG Rui <r@hev.cc>]

Introduce efi_get_kimg_kaslr_address() to compute the preferred
kernel image address dynamically when CONFIG_RANDOMIZE_BASE is
enabled. The function derives a random offset using EFI-provided
randomness combined with the timer 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.

Signed-off-by: WANG Rui <r@hev.cc>
---
 arch/loongarch/Kconfig                   |  2 +-
 arch/loongarch/include/asm/efi.h         |  4 +++-
 drivers/firmware/efi/libstub/loongarch.c | 16 ++++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 3b042dbb2c41..a5afb70f73d9 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -730,7 +730,7 @@ config RANDOMIZE_BASE
 config RANDOMIZE_BASE_MAX_OFFSET
 	hex "Maximum KASLR offset" if EXPERT
 	depends on RANDOMIZE_BASE
-	range 0x0 0x10000000
+	range 0x20000 0x10000000
 	default "0x01000000"
 	help
 	  When KASLR is active, this provides the maximum offset that will
diff --git a/arch/loongarch/include/asm/efi.h b/arch/loongarch/include/asm/efi.h
index eddc8e79b3fa..f831320efd41 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/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
index 9825f5218137..df67ef8c68ab 100644
--- a/drivers/firmware/efi/libstub/loongarch.c
+++ b/drivers/firmware/efi/libstub/loongarch.c
@@ -38,6 +38,22 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map, void *priv)
 	return EFI_SUCCESS;
 }
 
+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 ^= (rdtime_l() << 16);
+		random_offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - SZ_64K - 1);
+		random_offset = ALIGN(random_offset, SZ_64K) + SZ_64K;
+	}
+#endif
+
+	return PHYSADDR(VMLINUX_LOAD_ADDRESS) + random_offset;
+}
+
 unsigned long __weak kernel_entry_address(unsigned long kernel_addr,
 		efi_loaded_image_t *image)
 {
-- 
2.54.0