Re: [PATCH] module: Fix kernel panic when a symbol st_shndx is out of bounds

Petr Pavlu
2026-01-12T14:37:07Z

On 12/30/25 7:32 PM, Ihor Solodrai wrote:
> The module loader doesn't check for bounds of the ELF section index in
> simplify_symbols():
>
> for (i = 1; i < symsec->sh_size / sizeof(Elf_Sym); i++) {
> const char *name = info->strtab + sym[i].st_name;
>
> switch (sym[i].st_shndx) {
> case SHN_COMMON:
>
> [...]
>
> default:
> /* Divert to percpu allocation if a percpu var. */
> if (sym[i].st_shndx == info->index.pcpu)
> secbase = (unsigned long)mod_percpu(mod);
> else
> /** HERE --> **/ secbase = info->sechdrs[sym[i].st_shndx].sh_addr;
> sym[i].st_value += secbase;
> break;
> }
> }
>
> A symbol with an out-of-bounds st_shndx value, for example 0xffff
> (known as SHN_XINDEX or SHN_HIRESERVE), may cause a kernel panic:
>
> BUG: unable to handle page fault for address: ...
> RIP: 0010:simplify_symbols+0x2b2/0x480
> ...
> Kernel panic - not syncing: Fatal exception
>
> This can happen when module ELF is legitimately using SHN_XINDEX or
> when it is corrupted.
>
> Add a bounds check in simplify_symbols() to validate that st_shndx is
> within the valid range before using it.
>
> This issue was discovered due to a bug in llvm-objcopy, see relevant
> discussion for details [1].
>
> [1] https://lore.kernel.org/linux-modules/20251224005752.201911-1-ihor.solodrai@linux.dev/
>
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

--
Thanks,
Petr