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 3/7] bpf: enforce precision for r0 on callback return
Date: Thu, 09 Nov 2023 19:38:09 +0200 [thread overview]
Message-ID: <b335aa904dca981058e1db92b6270960f2a28948.camel@gmail.com> (raw)
In-Reply-To: <CAEf4BzY1-mcN5Wjf4-FOKQvnom+0EV=a=cGxvBO9=rbCS0kzwA@mail.gmail.com>
On Thu, 2023-11-09 at 09:32 -0800, Andrii Nakryiko wrote:
> On Thu, Nov 9, 2023 at 7:20 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
> >
> > On Mon, 2023-10-30 at 22:03 -0700, Andrii Nakryiko wrote:
> > > > Given verifier checks actual value, r0 has to be precise, so we need to
> > > > propagate precision properly.
> > > >
> > > > Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
> > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> >
> > I don't follow why this is necessary, could you please conjure
> > an example showing that current behavior is not safe?
> > This example could be used as a test case, as this change
> > seems to not be covered by test cases.
>
> We rely on callbacks to return specific value (0 or 1, for example),
> and use or might use that in kernel code. So if we rely on the
> specific value of a register, it has to be precise. Marking r0 as
> precise will have implications on other registers from which r0 was
> derived. This might have implications on state pruning and stuff. If
> r0 and its ancestors are not precise, we might erroneously assume some
> states are safe and prune them, even though they are not.
The r0 returned from bpf_loop's callback says bpf_loop to stop iteration,
bpf_loop returns the number of completed iterations. However, the return
value of bpf_loop modeled by verifier is unbounded scalar.
Same for map's for each.
I'm not sure we have callback calling functions that can expose this as a
safety issue.
[...]
next prev parent reply other threads:[~2023-11-09 17:38 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 [this message]
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
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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