linux-kernel - Re: [PATCH bpf-next v2] arm64: bpf: fix 32bit unconditional bswap

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Message-ID: <dec82e88-6961-4bf6-92b7-9acc753aaad4@huaweicloud.com>
Date: Thu, 21 Mar 2024 16:32:48 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: Artem Savkov <asavkov@...hat.com>, Xi Wang <xi.wang@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Cc: Catalin Marinas <catalin.marinas@....com>, linux-kernel@...r.kernel.org,
 Puranjay Mohan <puranjay12@...il.com>
Subject: Re: [PATCH bpf-next v2] arm64: bpf: fix 32bit unconditional bswap

On 3/21/2024 4:18 PM, Artem Savkov wrote:
> In case when is64 == 1 in emit(A64_REV32(is64, dst, dst), ctx) the
> generated insn reverses byte order for both high and low 32-bit words,
> resuling in an incorrect swap as indicated by the jit test:
> 
> [ 9757.262607] test_bpf: #312 BSWAP 16: 0x0123456789abcdef -> 0xefcd jited:1 8 PASS
> [ 9757.264435] test_bpf: #313 BSWAP 32: 0x0123456789abcdef -> 0xefcdab89 jited:1 ret 1460850314 != -271733879 (0x5712ce8a != 0xefcdab89)FAIL (1 times)
> [ 9757.266260] test_bpf: #314 BSWAP 64: 0x0123456789abcdef -> 0x67452301 jited:1 8 PASS
> [ 9757.268000] test_bpf: #315 BSWAP 64: 0x0123456789abcdef >> 32 -> 0xefcdab89 jited:1 8 PASS
> [ 9757.269686] test_bpf: #316 BSWAP 16: 0xfedcba9876543210 -> 0x1032 jited:1 8 PASS
> [ 9757.271380] test_bpf: #317 BSWAP 32: 0xfedcba9876543210 -> 0x10325476 jited:1 ret -1460850316 != 271733878 (0xa8ed3174 != 0x10325476)FAIL (1 times)
> [ 9757.273022] test_bpf: #318 BSWAP 64: 0xfedcba9876543210 -> 0x98badcfe jited:1 7 PASS
> [ 9757.274721] test_bpf: #319 BSWAP 64: 0xfedcba9876543210 >> 32 -> 0x10325476 jited:1 9 PASS
> 
> Fix this by forcing 32bit variant of rev32.
> 
> Fixes: 1104247f3f979 ("bpf, arm64: Support unconditional bswap")
> Signed-off-by: Artem Savkov <asavkov@...hat.com>
> Tested-by: Puranjay Mohan <puranjay12@...il.com>
> Acked-by: Puranjay Mohan <puranjay12@...il.com>
> ---
>   arch/arm64/net/bpf_jit_comp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index c5b461dda4385..c3ededd23cbf6 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -943,7 +943,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
>   			emit(A64_UXTH(is64, dst, dst), ctx);
>   			break;
>   		case 32:
> -			emit(A64_REV32(is64, dst, dst), ctx);
> +			emit(A64_REV32(0, dst, dst), ctx);
>   			/* upper 32 bits already cleared */
>   			break;
>   		case 64:

Acked-by: Xu Kuohai <xukuohai@...wei.com>