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

["Ard Biesheuvel" <ardb@kernel.org>]

On Wed, 29 Apr 2026, at 11:04, WANG Rui wrote:
> Hi Ard,
>
> On Wed, Apr 29, 2026 at 4:55 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>>
>>
>>
>> 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@hev.cc>
>> > ---
>> >  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()
>
> 1. drivers/firmware/efi/libstub/loongarch-stub.c
>
>   efi_status_t handle_kernel_image(...)
>   {
>       ...
>       status = efi_relocate_kernel(&kernel_addr, kernel_fsize, kernel_asize,
>                EFI_KIMG_PREFERRED_ADDRESS, efi_get_kimg_min_align(), 0x0);
>       ...
>   }
>
> 2. drivers/firmware/efi/libstub/zboot.c
>
>   static unsigned long alloc_preferred_address(...)
>   {
>   #ifdef EFI_KIMG_PREFERRED_ADDRESS
>       efi_physical_addr_t efi_addr = EFI_KIMG_PREFERRED_ADDRESS;
>
>       if (efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS, EFI_LOADER_DATA,
>               alloc_size / EFI_PAGE_SIZE, &efi_addr) == EFI_SUCCESS)
>           return efi_addr;
>   #endif
>       return ULONG_MAX;
>   }
>

Ah apologies - I misread the patch.