Re: [PATCH 3/4] efi: loader: fix SizeOfBlock underflow in relocation processing

Ahmad Fatoum
2026-04-14T08:47:53Z

On 4/13/26 2:36 PM, Sascha Hauer wrote:
> From: Sascha Hauer <sascha@saschahauer.de>
>
> rel->SizeOfBlock is a uint32_t read from the PE image. If it is smaller
> than sizeof(IMAGE_BASE_RELOCATION) (8 bytes), the subtraction
> SizeOfBlock - sizeof(*rel) underflows. On 32-bit architectures (ARM,
> i386, riscv32) the resulting huge unsigned value divided by 2 fits in a
> positive int, causing the relocation loop to iterate billions of times,
> reading and writing far past the relocation block.
>
> Reject relocation blocks with SizeOfBlock smaller than the base
> relocation header.
>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
>
> Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

> ---
> efi/loader/pe.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/efi/loader/pe.c b/efi/loader/pe.c
> index 3190718df5..ea385c8795 100644
> --- a/efi/loader/pe.c
> +++ b/efi/loader/pe.c
> @@ -120,6 +120,10 @@ static efi_status_t efi_loader_relocate(const IMAGE_BASE_RELOCATION *rel,
> end = (const IMAGE_BASE_RELOCATION *)((const char *)rel + rel_size);
> while (rel + 1 < end && rel->SizeOfBlock) {
> const uint16_t *relocs = (const uint16_t *)(rel + 1);
> +
> + if (rel->SizeOfBlock < sizeof(*rel))
> + return EFI_LOAD_ERROR;
> +
> i = (rel->SizeOfBlock - sizeof(*rel)) / sizeof(uint16_t);
> while (i--) {
> uint32_t offset = (uint32_t)(*relocs & 0xfff) +

--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |