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From: Martin KaFai Lau <kafai@fb.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH bpf-next 3/4] bpf: selftest: A bpf prog that has a 32bit scalar spill
Date: Tue, 21 Sep 2021 16:52:29 -0700	[thread overview]
Message-ID: <20210921235229.6jiri54fji6kiipe@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210921023234.pjnby3s4q4o4agwe@ast-mbp>

On Mon, Sep 20, 2021 at 07:32:34PM -0700, Alexei Starovoitov wrote:
> On Mon, Sep 20, 2021 at 06:31:22PM -0700, Martin KaFai Lau wrote:
> > It is a simplified example that can trigger a 32bit scalar spill.
> > The const scalar is refilled and added to a skb->data later.
> > Since the reg state of the 32bit scalar spill is not saved now,
> > adding the refilled reg to skb->data and then comparing it with
> > skb->data_end cannot verify the skb->data access.
> > 
> > With the earlier verifier patch and the llvm patch [1].  The verifier
> > can correctly verify the bpf prog.
> 
> Let's land llvm patch and wait until CI picks up the new llvm build?
> Please add a comment to selftests/bpf/README.rst that describes
> the failing test when llvm is old.
> I'm guessing there is no easier way to reliably skip the test
> in such situation, since failure to load might be the result
> of some future changes.
> llvm version check won't work either.
> 
> the patch 2 looks correct to me. I couldn't spot any issue with the logic.
Thanks for the review.  I also don't see an easy way to detect and skip it
reliably.  I will update the README.rst and also the error message from
the xdpwall selftest.

  reply	other threads:[~2021-09-21 23:52 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-21  1:31 [PATCH bpf-next 0/4] bpf: Support <8-byte scalar spill and refill Martin KaFai Lau
2021-09-21  1:31 ` [PATCH bpf-next 1/4] bpf: Check the other end of slot_type for STACK_SPILL Martin KaFai Lau
2021-09-21  1:31 ` [PATCH bpf-next 2/4] bpf: Support <8-byte scalar spill and refill Martin KaFai Lau
2021-09-21  1:31 ` [PATCH bpf-next 3/4] bpf: selftest: A bpf prog that has a 32bit scalar spill Martin KaFai Lau
2021-09-21  2:32   ` Alexei Starovoitov
2021-09-21 23:52     ` Martin KaFai Lau [this message]
2021-09-21  1:31 ` [PATCH bpf-next 4/4] bpf: selftest: Add verifier tests for <8-byte scalar spill and refill Martin KaFai Lau

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