From: Yonghong Song <yonghong.song@linux.dev>
To: Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
martin.lau@kernel.org
Cc: kernel-team@meta.com, Maxim Mikityanskiy <maxtram95@gmail.com>
Subject: Re: [PATCH bpf-next] bpf: ensure precise is reset to false in __mark_reg_const_zero()
Date: Fri, 15 Dec 2023 18:44:35 -0800 [thread overview]
Message-ID: <725bd1ef-94f0-4f2e-b3ba-d6842d291270@linux.dev> (raw)
In-Reply-To: <20231215235822.908223-1-andrii@kernel.org>
On 12/15/23 3:58 PM, Andrii Nakryiko wrote:
> It is safe to always start with imprecise SCALAR_VALUE register.
> Previously __mark_reg_const_zero() relied on caller to reset precise
> mark, but it's very error prone and we already missed it in a few
> places. So instead make __mark_reg_const_zero() reset precision always,
> as it's a safe default for SCALAR_VALUE. Explanation is basically the
> same as for why we are resetting (or rather not setting) precision in
> current state. If necessary, precision propagation will set it to
> precise correctly.
>
> As such, also remove a big comment about forward precision propagation
> in mark_reg_stack_read() and avoid unnecessarily setting precision to
> true after reading from STACK_ZERO stack. Again, precision propagation
> will correctly handle this, if that SCALAR_VALUE register will ever be
> needed to be precise.
>
> Reported-by: Maxim Mikityanskiy <maxtram95@gmail.com>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
next prev parent reply other threads:[~2023-12-16 2:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-15 23:58 [PATCH bpf-next] bpf: ensure precise is reset to false in __mark_reg_const_zero() Andrii Nakryiko
2023-12-16 2:44 ` Yonghong Song [this message]
2023-12-16 15:13 ` Maxim Mikityanskiy
2023-12-18 10:46 ` Daniel Borkmann
2023-12-18 17:18 ` Andrii Nakryiko
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