From: Eduard Zingerman <eddyz87@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
martin.lau@kernel.org, kernel-team@meta.com
Subject: Re: [PATCH bpf-next 6/7] bpf: preserve constant zero when doing partial register restore
Date: Thu, 09 Nov 2023 21:34:51 +0200 [thread overview]
Message-ID: <fa3ad5ba2a36de906cab33e1f1b2ce39b37c06c2.camel@gmail.com> (raw)
In-Reply-To: <CAEf4BzbmCngJeThcwUt52f7nNqOUtfOury3KfCrr+QiYKVX74w@mail.gmail.com>
On Thu, 2023-11-09 at 09:41 -0800, Andrii Nakryiko wrote:
> On Thu, Nov 9, 2023 at 7:21 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
> >
> > On Mon, 2023-10-30 at 22:03 -0700, Andrii Nakryiko wrote:
> > > Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from
> > > stack from slot that has register spilled into it and that register has
> > > a constant value zero, preserve that zero and mark spilled register as
> > > precise for that. This makes spilled const zero register and STACK_ZERO
> > > cases equivalent in their behavior.
> > >
> > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> >
> > Could you please add a test case?
> >
>
> There is already at least one test case that relies on this behavior
> :) But yep, I'll add a dedicated test.
Thank you. Having a dedicated test always helps with debugging, should
something go wrong.
[...]
> > Condition for this branch is (off % BPF_REG_SIZE != 0) || size != spill_size,
> > is it necessary to check for some unusual offsets, e.g. off % BPF_REG_SIZE == 7
> > or something like that?
>
> I don't think so. We rely on all bytes we are reading to be either
> spills (and thus spill_cnt == size), in which case verifier logic
> makes sure we have spill at slot boundary (off % BPF_REG_SIZE == 0).
> Or it's all STACK_ZERO, and then zero_cnt == size, in which case we
> know it's zero.
>
> Unless I missed something else?
False alarm, 'slot' is derived from 'off' and the loop checks
'type = stype[(slot - i) % BPF_REG_SIZE];', sorry for the noise.
next prev parent reply other threads:[~2023-11-09 19:34 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-31 5:03 [PATCH bpf-next 0/7] Complete BPF verifier precision tracking support for register spills Andrii Nakryiko
2023-10-31 5:03 ` [PATCH bpf-next 1/7] bpf: use common jump (instruction) history across all states Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-11-09 16:13 ` Alexei Starovoitov
2023-11-09 17:28 ` Andrii Nakryiko
2023-11-09 19:29 ` Alexei Starovoitov
2023-11-09 19:49 ` Andrii Nakryiko
2023-11-09 20:39 ` Andrii Nakryiko
2023-11-09 22:05 ` Alexei Starovoitov
2023-11-09 22:57 ` Andrii Nakryiko
2023-11-11 4:29 ` Andrii Nakryiko
2023-10-31 5:03 ` [PATCH bpf-next 2/7] bpf: support non-r10 register spill/fill to/from stack in precision tracking Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-11-09 17:20 ` Andrii Nakryiko
2023-11-09 18:20 ` Eduard Zingerman
2023-11-10 5:48 ` Andrii Nakryiko
2023-11-12 1:57 ` Andrii Nakryiko
2023-11-12 14:05 ` Eduard Zingerman
2023-10-31 5:03 ` [PATCH bpf-next 3/7] bpf: enforce precision for r0 on callback return Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-11-09 17:32 ` Andrii Nakryiko
2023-11-09 17:38 ` Eduard Zingerman
2023-11-09 17:50 ` Andrii Nakryiko
2023-11-09 17:58 ` Alexei Starovoitov
2023-11-09 18:01 ` Andrii Nakryiko
2023-11-09 18:03 ` Eduard Zingerman
2023-11-09 18:00 ` Eduard Zingerman
2023-10-31 5:03 ` [PATCH bpf-next 4/7] bpf: fix check for attempt to corrupt spilled pointer Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-10-31 5:03 ` [PATCH bpf-next 5/7] bpf: preserve STACK_ZERO slots on partial reg spills Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-11-09 17:37 ` Andrii Nakryiko
2023-11-09 17:54 ` Eduard Zingerman
2023-10-31 5:03 ` [PATCH bpf-next 6/7] bpf: preserve constant zero when doing partial register restore Andrii Nakryiko
2023-11-09 15:20 ` Eduard Zingerman
2023-11-09 17:41 ` Andrii Nakryiko
2023-11-09 19:34 ` Eduard Zingerman [this message]
2023-10-31 5:03 ` [PATCH bpf-next 7/7] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Andrii Nakryiko
2023-10-31 5:22 ` Andrii Nakryiko
2023-11-01 7:56 ` Jiri Olsa
2023-11-01 16:27 ` Andrii Nakryiko
2023-11-02 9:54 ` Jiri Olsa
2023-11-09 15:21 ` Eduard Zingerman
2023-11-09 17:43 ` Andrii Nakryiko
2023-11-09 17:44 ` Eduard Zingerman
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