Re: [PATCH v2 1/2] efi/loongarch: Randomize kernel preferred address for KASLR

Hi, Rui,

On Tue, Apr 28, 2026 at 12:02 PM WANG Rui <[email protected]> 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 <[email protected]>
> ---
>  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..c44be5d3dc04 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)
Move it into arch/loongarch/include/asm/efi.h?

> +{
> +       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 - SZ_64K - 1);
I still don't want to modify the range of RANDOMIZE_BASE_MAX_OFFSET, so use
     random_offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1)
here?

> +               random_offset = ALIGN(random_offset, SZ_64K) + SZ_64K;
It seems "random_offset = ALIGN(random_offset + SZ64K, SZ_64K)" is better.

Huacai

> +       }
> +#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
>