Re: [PATCH] x86/kaslr: try process e820 entries if can not get suitable regions from efi

[Ard Biesheuvel]

(cc Arvind)

On Tue, 5 Jan 2021 at 09:54, Lin Feng <linfeng23@xxxxxxxxxx> wrote:
>
> On efi64 x86_64 system, the EFI_CONVENTIONAL_MEMORY regions will not
> be mapped when making EFI runtime calls. So kexec-tools can not get
> these from /sys/firmware/efi/runtime-map. Then compressed boot os
> can not get suitable regions in process_efi_entries and print debug
> message as follow:
>         Physical KASLR disabled: no suitable memory region!
> To enable physical kaslr with kexec, call process_e820_entries when
> no suitable regions in efi memmaps.
>
> Signed-off-by: Lin Feng <linfeng23@xxxxxxxxxx>
>
> ---
>
> I find a regular of Kernel code and data placement with kexec. It
> seems unsafe. The reason is showed above.
>
> I'm not familiar with efi firmware. I wonder if there are some risks
> to get regions according to e820 when there is no suitable region
> in efi memmaps.
> ---
>  arch/x86/boot/compressed/kaslr.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index b92fffbe761f..dbd7244b71aa 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -685,6 +685,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
>  {
>         struct efi_info *e = &boot_params->efi_info;
>         bool efi_mirror_found = false;
> +       bool efi_mem_region_found = false;
>         struct mem_vector region;
>         efi_memory_desc_t *md;
>         unsigned long pmap;
> @@ -742,12 +743,13 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
>                     !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
>                         continue;
>
> +               efi_mem_region_found = false;
>                 region.start = md->phys_addr;
>                 region.size = md->num_pages << EFI_PAGE_SHIFT;
>                 if (process_mem_region(&region, minimum, image_size))
>                         break;
>         }
> -       return true;
> +       return efi_mem_region_found;
>  }
>  #else
>  static inline bool
> --
> 2.23.0
>