From: Daniel Borkmann <daniel@iogearbox.net>
To: "Björn Töpel" <bjorn.topel@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Netdev <netdev@vger.kernel.org>,
linux-riscv@lists.infradead.org, bpf <bpf@vger.kernel.org>,
Jiong Wang <jiong.wang@netronome.com>
Subject: Re: [PATCH bpf] bpf, riscv: clear target register high 32-bits for and/or/xor on ALU32
Date: Thu, 23 May 2019 15:58:00 +0200 [thread overview]
Message-ID: <412b2dda-7507-c291-9787-7a35a7e1bfd6@iogearbox.net> (raw)
In-Reply-To: <CAJ+HfNifkxKz8df7gLBuqWA6+t6awrrRK6oW6m1nAYETJD+Vfg@mail.gmail.com>
On 05/21/2019 04:12 PM, Björn Töpel wrote:
> On Tue, 21 May 2019 at 16:02, Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 05/21/2019 03:46 PM, Björn Töpel wrote:
>>> When using 32-bit subregisters (ALU32), the RISC-V JIT would not clear
>>> the high 32-bits of the target register and therefore generate
>>> incorrect code.
>>>
>>> E.g., in the following code:
>>>
>>> $ cat test.c
>>> unsigned int f(unsigned long long a,
>>> unsigned int b)
>>> {
>>> return (unsigned int)a & b;
>>> }
>>>
>>> $ clang-9 -target bpf -O2 -emit-llvm -S test.c -o - | \
>>> llc-9 -mattr=+alu32 -mcpu=v3
>>> .text
>>> .file "test.c"
>>> .globl f
>>> .p2align 3
>>> .type f,@function
>>> f:
>>> r0 = r1
>>> w0 &= w2
>>> exit
>>> .Lfunc_end0:
>>> .size f, .Lfunc_end0-f
>>>
>>> The JIT would not clear the high 32-bits of r0 after the
>>> and-operation, which in this case might give an incorrect return
>>> value.
>>>
>>> After this patch, that is not the case, and the upper 32-bits are
>>> cleared.
>>>
>>> Reported-by: Jiong Wang <jiong.wang@netronome.com>
>>> Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
>>> Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
>>
>> Was this missed because test_verifier did not have test coverage?
>
> Yup, and Jiong noted it.
Applied, thanks!
prev parent reply other threads:[~2019-05-23 13:58 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-21 13:46 [PATCH bpf] bpf, riscv: clear target register high 32-bits for and/or/xor on ALU32 Björn Töpel
2019-05-21 14:02 ` Daniel Borkmann
2019-05-21 14:12 ` Björn Töpel
2019-05-23 13:58 ` Daniel Borkmann [this message]
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