linux-kernel - bpf: misleading spec_v1 check on variable-offset stack read?

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Message-ID: <ff8135a6-506f-330f-89fb-f98672467b27@cs.fau.de>
Date:   Wed, 15 Mar 2023 17:51:19 +0100
From:   Luis Gerhorst <gerhorst@...fau.de>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Andrei Matei <andreimatei1@...il.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: bpf: misleading spec_v1 check on variable-offset stack read?

Hello,

is there any way to introduce variable-offset (stack) pointers without 
using pointer arithmetic (BPF_ADD/SUB)? If yes, I believe this is a 
security issue because these can be used in stack writes. If not, I 
think the patch sent in reply to this mail should be applied. (I was not 
able to find any indication that the former is the case.)

Best regards,
Luis


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