From: Daniel Borkmann <daniel@iogearbox.net>
To: Luke Nelson <lukenels@cs.washington.edu>, linux-kernel@vger.kernel.org
Cc: "Luke Nelson" <luke.r.nels@gmail.com>,
"Xi Wang" <xi.wang@gmail.com>,
"Wang YanQing" <udknight@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
"Alexey Kuznetsov" <kuznet@ms2.inr.ac.ru>,
"Hideaki YOSHIFUJI" <yoshfuji@linux-ipv6.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, "Alexei Starovoitov" <ast@kernel.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"Shuah Khan" <shuah@kernel.org>,
"Jakub Kicinski" <jakub.kicinski@netronome.com>,
"Jiong Wang" <jiong.wang@netronome.com>,
"Björn Töpel" <bjorn.topel@gmail.com>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf 1/3] bpf, x32: Fix bug with ALU64 {LSH,RSH,ARSH} BPF_X shift by 0
Date: Wed, 3 Jul 2019 11:49:47 +0200 [thread overview]
Message-ID: <5c2080f4-532e-d239-13b1-4a5a620f6c33@iogearbox.net> (raw)
In-Reply-To: <20190629055759.28365-1-luke.r.nels@gmail.com>
On 06/29/2019 07:57 AM, Luke Nelson wrote:
> The current x32 BPF JIT for shift operations is not correct when the
> shift amount in a register is 0. The expected behavior is a no-op, whereas
> the current implementation changes bits in the destination register.
>
> The following example demonstrates the bug. The expected result of this
> program is 1, but the current JITed code returns 2.
>
> r0 = 1
> r1 = 1
> r2 = 0
> r1 <<= r2
> if r1 == 1 goto end
> r0 = 2
> end:
> exit
>
> The bug is caused by an incorrect assumption by the JIT that a shift by
> 32 clear the register. On x32 however, shifts use the lower 5 bits of
> the source, making a shift by 32 equivalent to a shift by 0.
>
> This patch fixes the bug using double-precision shifts, which also
> simplifies the code.
>
> Fixes: 03f5781be2c7 ("bpf, x86_32: add eBPF JIT compiler for ia32")
> 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>
Series applied, thanks!
prev parent reply other threads:[~2019-07-03 9:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-29 5:57 [PATCH bpf 1/3] bpf, x32: Fix bug with ALU64 {LSH,RSH,ARSH} BPF_X shift by 0 Luke Nelson
2019-06-29 5:57 ` [PATCH bpf 2/3] bpf, x32: Fix bug with ALU64 {LSH,RSH,ARSH} BPF_K " Luke Nelson
2019-06-29 5:57 ` [PATCH bpf 3/3] selftests: bpf: add tests for shifts by zero Luke Nelson
2019-07-03 9:49 ` Daniel Borkmann [this message]
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