From: Eduard Zingerman <eddyz87@gmail.com>
To: Hao Sun <sunhao.th@gmail.com>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrei Matei <andreimatei1@gmail.com>,
bpf@vger.kernel.org, ast@kernel.org,
kernel-team@dataexmachina.dev
Subject: Re: [PATCH bpf] bpf: fix tracking of stack size for var-off access
Date: Wed, 22 Nov 2023 14:46:09 +0200 [thread overview]
Message-ID: <dc1a84bde2c62445b2bd05ea99dfc716d4724f6c.camel@gmail.com> (raw)
In-Reply-To: <CACkBjsbWdOVMs7vRXvxi0MCoOAh+skYWFN1douBjkRzeTX=wvg@mail.gmail.com>
On Tue, 2023-11-21 at 18:16 +0100, Hao Sun wrote:
[...]
> Yet, the sample direct read would be rejected:
>
> func#0 @0
> 0: R1=ctx() R10=fp0
> 0: (bf) r6 = r10 ; R6_w=fp0 R10=fp0
> 1: (61) r7 = *(u32 *)(r6 -200)
> invalid read from stack R6 off=-200 size=4
>
> Eduard, you added support for reading uninit slots, should we also add something
> like the following:
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 8c2d31aa3d31..aa861d2da240 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -6446,7 +6446,7 @@ static int check_stack_slot_within_bounds(int off,
> {
> int min_valid_off;
>
> - if (t == BPF_WRITE)
> + if (t == BPF_WRITE || env->allow_uninit_stack)
> min_valid_off = -MAX_BPF_STACK;
> else
> min_valid_off = -state->allocated_stack;
I agree with your logic and this change seems reasonable.
Sorry for delayed response.
next prev parent reply other threads:[~2023-11-22 12:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-13 23:50 [PATCH bpf] bpf: fix tracking of stack size for var-off access Andrei Matei
2023-11-21 0:46 ` Andrii Nakryiko
2023-11-21 17:16 ` Hao Sun
2023-11-21 20:29 ` Andrei Matei
2023-11-21 21:55 ` Andrii Nakryiko
2023-11-22 12:38 ` Eduard Zingerman
2023-11-22 12:46 ` Eduard Zingerman [this message]
2023-11-21 20:34 ` Andrei Matei
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