From: Eduard Zingerman <eddyz87@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>, bpf@vger.kernel.org
Cc: Nicholas Carlini <npc@anthropic.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Emil Tsalapatis <emil@etsalapatis.com>,
kkd@meta.com, kernel-team@meta.com
Subject: Re: [PATCH bpf v1 5/8] bpf: Mark NULL kptr stores precise
Date: Fri, 04 Sep 2026 09:35:16 -0700 [thread overview]
Message-ID: <40418ce913972dc14276a2e8954cd63595c5eee6.camel@gmail.com> (raw)
In-Reply-To: <20260904104203.345917-6-memxor@gmail.com>
On Fri, 2026-09-04 at 12:41 +0200, Kumar Kartikeya Dwivedi wrote:
> check_map_kptr_access() permits a scalar store into an untrusted kptr
> field only when the register is known to contain zero. Unlike other
> verifier checks whose outcome depends on a scalar value, it does not mark
> that register precise.
>
> A state checkpoint reached with an imprecise zero can therefore prune a
> second path that reaches the store with an arbitrary nonzero scalar. The
> program can write attacker-controlled bits into the kptr field and load
> them back as a PTR_TO_BTF_ID.
>
> Call mark_chain_precision() before accepting a known-zero register. This
> forces state equivalence to compare its scalar range and makes the verifier
> visit and reject a path carrying a nonzero value.
>
> Fixes: 61df10c7799e ("bpf: Allow storing unreferenced kptr in map")
> Reported-by: Nicholas Carlini <npc@anthropic.com>
> Suggested-by: Nicholas Carlini <npc@anthropic.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
...
next prev parent reply other threads:[~2026-09-04 16:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-04 10:41 [PATCH bpf v1 0/8] Misc bug fixes - part 4 Kumar Kartikeya Dwivedi
2026-09-04 10:41 ` [PATCH bpf v1 1/8] bpf: Preserve special fields in recycled rhtab elements Kumar Kartikeya Dwivedi
2026-09-04 10:41 ` [PATCH bpf v1 2/8] selftests/bpf: Test timer field on recycled rhtab element Kumar Kartikeya Dwivedi
2026-09-04 11:12 ` sashiko-bot
2026-09-04 11:47 ` bot+bpf-ci
2026-09-04 10:41 ` [PATCH bpf v1 3/8] bpf: Cancel special fields when recycling rhtab elements Kumar Kartikeya Dwivedi
2026-09-04 11:37 ` sashiko-bot
2026-09-04 11:41 ` Kumar Kartikeya Dwivedi
2026-09-04 11:47 ` bot+bpf-ci
2026-09-04 10:41 ` [PATCH bpf v1 4/8] selftests/bpf: Test rhtab kptr cancellation semantics Kumar Kartikeya Dwivedi
2026-09-04 10:41 ` [PATCH bpf v1 5/8] bpf: Mark NULL kptr stores precise Kumar Kartikeya Dwivedi
2026-09-04 12:12 ` sashiko-bot
2026-09-04 16:35 ` Eduard Zingerman [this message]
2026-09-04 10:41 ` [PATCH bpf v1 6/8] selftests/bpf: Test imprecise scalar kptr stores Kumar Kartikeya Dwivedi
2026-09-04 11:47 ` bot+bpf-ci
2026-09-04 10:41 ` [PATCH bpf v1 7/8] bpf: Preserve inner map identity in callback frames Kumar Kartikeya Dwivedi
2026-09-04 11:47 ` bot+bpf-ci
2026-09-04 10:41 ` [PATCH bpf v1 8/8] selftests/bpf: Test inner map identities in callbacks Kumar Kartikeya Dwivedi
2026-09-04 11:47 ` bot+bpf-ci
2026-09-04 19:30 ` [PATCH bpf v1 0/8] Misc bug fixes - part 4 patchwork-bot+netdevbpf
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