From: Puranjay Mohan <puranjay12@gmail.com>
To: Ilya Leoshkevich <iii@linux.ibm.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>
Cc: bpf@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Ilya Leoshkevich <iii@linux.ibm.com>
Subject: Re: [PATCH bpf-next v2 01/10] bpf: Disable zero-extension for BPF_MEMSX
Date: Thu, 21 Sep 2023 12:35:57 +0000 [thread overview]
Message-ID: <mb61pleczk8k2.fsf@gmail.com> (raw)
In-Reply-To: <20230919101336.2223655-2-iii@linux.ibm.com>
Ilya Leoshkevich <iii@linux.ibm.com> writes:
> On the architectures that use bpf_jit_needs_zext(), e.g., s390x, the
> verifier incorrectly inserts a zero-extension after BPF_MEMSX, leading
> to miscompilations like the one below:
>
> 24: 89 1a ff fe 00 00 00 00 "r1 = *(s16 *)(r10 - 2);" # zext_dst set
> 0x3ff7fdb910e: lgh %r2,-2(%r13,%r0) # load halfword
> 0x3ff7fdb9114: llgfr %r2,%r2 # wrong!
> 25: 65 10 00 03 00 00 7f ff if r1 s> 32767 goto +3 <l0_1> # check_cond_jmp_op()
>
> Disable such zero-extensions. The JITs need to insert sign-extension
> themselves, if necessary.
>
> Suggested-by: Puranjay Mohan <puranjay12@gmail.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
> kernel/bpf/verifier.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index a7178ecf676d..614bf3fa4fd5 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3114,7 +3114,7 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn,
>
> if (class == BPF_LDX) {
> if (t != SRC_OP)
> - return BPF_SIZE(code) == BPF_DW;
> + return BPF_SIZE(code) == BPF_DW || BPF_MODE(code) == BPF_MEMSX;
> /* LDX source must be ptr. */
> return true;
> }
> --
> 2.41.0
Reviewed-by: Puranjay Mohan <puranjay12@gmail.com>
Thanks for this.
Puranjay
next prev parent reply other threads:[~2023-09-21 18:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-19 10:09 [PATCH bpf-next v2 00/10] Implement cpuv4 support for s390x Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 01/10] bpf: Disable zero-extension for BPF_MEMSX Ilya Leoshkevich
2023-09-21 12:35 ` Puranjay Mohan [this message]
2023-09-19 10:09 ` [PATCH bpf-next v2 02/10] selftests/bpf: Unmount the cgroup2 work directory Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 03/10] selftests/bpf: Add big-endian support to the ldsx test Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 04/10] s390/bpf: Implement BPF_MOV | BPF_X with sign-extension Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 05/10] s390/bpf: Implement BPF_MEMSX Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 06/10] s390/bpf: Implement unconditional byte swap Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 07/10] s390/bpf: Implement unconditional jump with 32-bit offset Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 08/10] s390/bpf: Implement signed division Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 09/10] selftests/bpf: Enable the cpuv4 tests for s390x Ilya Leoshkevich
2023-09-19 10:09 ` [PATCH bpf-next v2 10/10] selftests/bpf: Trim DENYLIST.s390x Ilya Leoshkevich
2023-09-21 21:30 ` [PATCH bpf-next v2 00/10] Implement cpuv4 support for s390x patchwork-bot+netdevbpf
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