linux-kernel - Re: CVE-2023-52920: bpf: support non-r10 register spill/fill to/from stack in precision tracking

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Message-ID: <6ff5182d2cdc4601834bfaa1e3cd1db3@epfl.ch>
Date: Fri, 8 Nov 2024 07:59:22 +0000
From: Tao Lyu <tao.lyu@...l.ch>
To: "eddyz87@...il.com" <eddyz87@...il.com>, Shung-Hsi Yu
	<shung-hsi.yu@...e.com>, Andrii Nakryiko <andrii@...nel.org>,
	"cve@...nel.org" <cve@...nel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: CVE-2023-52920: bpf: support non-r10 register spill/fill to/from
 stack in precision tracking

>> Hi Andrii and Eduard,
>
> Hi Shung-Hsi,
>
>> I'm trying to determine the security implication of CVE-2023-52920, or
>> more specifically, what does commit 41f6f64e6999 ("bpf: support non-r10
>> register spill/fill to/from stack in precision tracking") fix.
>> Superficially this looks more like an improvement to the verifier.
>
> It is my understanding as well, that this commit is an optimization to
> avoid some precision marks. I do not see any security implications.
>
> Thanks,
> Eduard
> 
> [...]

Hi Andrii, Eduard, and Shung-Hsi,

The previous discussion is here: https://lore.kernel.org/bpf/20231020155842.130257-1-tao.lyu@epfl.ch/ 

In short, without this patch, the verifier will miss checking an execution path that can have out-of-bound access,
which eventually leads to privilege escalation, like obtaining the root privilege.

Best,
Tao