From: "Björn Töpel" <bjorn.topel@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiong Wang <jiong.wang@netronome.com>,
Netdev <netdev@vger.kernel.org>,
linux-riscv@lists.infradead.org, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [PATCH bpf] bpf, riscv: clear target register high 32-bits for and/or/xor on ALU32
Date: Tue, 21 May 2019 16:12:12 +0200 [thread overview]
Message-ID: <CAJ+HfNifkxKz8df7gLBuqWA6+t6awrrRK6oW6m1nAYETJD+Vfg@mail.gmail.com> (raw)
In-Reply-To: <49999b2d-f025-894a-be61-a52d13b24678@iogearbox.net>
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.
> If so, could you follow-up with alu32 test cases for it, so other
> JITs can be tracked for these kind of issue as well. We should
> probably have one for every alu32 alu op to make sure it's not
> forgotten anywhere.
>
I'll hack a test_verifier test right away.
Thanks,
Björn
> Thanks,
> Daniel
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next prev parent reply other threads:[~2019-05-21 14:12 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 [this message]
2019-05-23 13:58 ` Daniel Borkmann
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