From: Daniel Borkmann <daniel@iogearbox.net>
To: Luke Nelson <lukenels@cs.washington.edu>, bpf@vger.kernel.org
Cc: Luke Nelson <luke.r.nels@gmail.com>, Xi Wang <xi.wang@gmail.com>,
Shubham Bansal <illusionist.neo@gmail.com>,
Russell King <linux@armlinux.org.uk>,
Alexei Starovoitov <ast@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
"David S. Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf] arm: bpf: Fix bugs with ALU64 {RSH, ARSH} BPF_K shift by 0
Date: Thu, 9 Apr 2020 01:17:01 +0200 [thread overview]
Message-ID: <65cdd042-c037-d7c8-e6e7-bcfb6e8b00cb@iogearbox.net> (raw)
In-Reply-To: <20200408181229.10909-1-luke.r.nels@gmail.com>
On 4/8/20 8:12 PM, Luke Nelson wrote:
> The current arm BPF JIT does not correctly compile RSH or ARSH when the
> immediate shift amount is 0. This causes the "rsh64 by 0 imm" and "arsh64
> by 0 imm" BPF selftests to hang the kernel by reaching an instruction
> the verifier determines to be unreachable.
>
> The root cause is in how immediate right shifts are encoded on arm.
> For LSR and ASR (logical and arithmetic right shift), a bit-pattern
> of 00000 in the immediate encodes a shift amount of 32. When the BPF
> immediate is 0, the generated code shifts by 32 instead of the expected
> behavior (a no-op).
>
> This patch fixes the bugs by adding an additional check if the BPF
> immediate is 0. After the change, the above mentioned BPF selftests pass.
>
> Fixes: 39c13c204bb11 ("arm: eBPF JIT compiler")
> Co-developed-by: Xi Wang <xi.wang@gmail.com>
> Signed-off-by: Xi Wang <xi.wang@gmail.com>
> Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Yikes, thanks for fixing, applied. Looks like noone was running BPF kselftests
on arm32 for quite a while. :(
prev parent reply other threads:[~2020-04-08 23:17 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-08 18:12 Luke Nelson
2020-04-08 23:17 ` Daniel Borkmann [this message]
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