Re: [PATCH v3 1/3] efi/loongarch: Randomize kernel preferred address for KASLR

[Ard Biesheuvel]

On Wed, 29 Apr 2026, at 07:13, WANG Rui wrote:
> 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@xxxxxx>
> ---
>  arch/loongarch/include/asm/efi.h         |  4 +++-
>  drivers/firmware/efi/libstub/loongarch.c | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> 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);
> +

Where is the call to this function being added?

> +#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..51997a0e83bd 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 ^= (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;
> +}
> +
>  unsigned long __weak kernel_entry_address(unsigned long kernel_addr,
>  		efi_loaded_image_t *image)
>  {
> -- 
> 2.54.0