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

[WANG Rui]

Hi Ard,

On Wed, Apr 29, 2026 at 4:55 PM Ard Biesheuvel <ardb@xxxxxxxxxx> 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@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()

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;
  }

Thanks,
Rui

> >
> >  #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