linux-kernel - Re: [PATCH] module: Fix kernel panic when a symbol st

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Message-ID: <d683a5c5-51ad-4b8e-bf8e-6a0526f7c9c1@suse.com>
Date: Mon, 12 Jan 2026 15:37:04 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Daniel Gomez <da.gomez@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, linux-kernel@...r.kernel.org,
 linux-modules@...r.kernel.org, bpf@...r.kernel.org,
 linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] module: Fix kernel panic when a symbol st_shndx is out of
 bounds

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@...ux.dev>

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

-- 
Thanks,
Petr