[PATCH v5 4/9] bpf/arm64: mask shift count per RFC 9669

[Marat Khalili]

> -----Original Message-----
> From: Stephen Hemminger <stephen at networkplumber.org>
> Sent: Wednesday 24 June 2026 18:55
> To: dev at dpdk.org
> Cc: Stephen Hemminger <stephen at networkplumber.org>; stable at dpdk.org; Wathsala Vithanage
> <wathsala.vithanage at arm.com>; Konstantin Ananyev <konstantin.ananyev at huawei.com>; Marat Khalili
> <marat.khalili at huawei.com>; Jerin Jacob <jerinj at marvell.com>
> Subject: [PATCH v5 4/9] bpf/arm64: mask shift count per RFC 9669
> 
> The ARM JIT was not masking the shift count as required by RFC 9669
> (0x3f for 64-bit, 0x1f for 32-bit), so large immediate shift counts
> overflowed the UBFM/SBFM encoding and failed the JIT. Mask the
> immediate in emit_lsl/emit_lsr/emit_asr.
> 
> Fixes: 9f4469d9e83a ("bpf/arm: add logical operations")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>

Acked-by: Marat Khalili <marat.khalili at huawei.com>

> ---
>  lib/bpf/bpf_jit_arm64.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/bpf/bpf_jit_arm64.c b/lib/bpf/bpf_jit_arm64.c
> index ba7ae4d680..7582370062 100644
> --- a/lib/bpf/bpf_jit_arm64.c
> +++ b/lib/bpf/bpf_jit_arm64.c
> @@ -545,12 +545,14 @@ emit_bitfield(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t rn,
>  	emit_insn(ctx, insn, check_reg(rd) || check_reg(rn) ||
>  		  check_immr_imms(is64, immr, imms));
>  }
> +
>  static void
>  emit_lsl(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
>  {
>  	const unsigned int width = is64 ? 64 : 32;
>  	uint8_t imms, immr;
> 
> +	imm &= width - 1;
>  	immr = (width - imm) & (width - 1);
>  	imms = width - 1 - imm;
> 
> @@ -560,13 +562,19 @@ emit_lsl(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
>  static void
>  emit_lsr(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
>  {
> -	emit_bitfield(ctx, is64, rd, rd, imm, is64 ? 63 : 31, A64_UBFM);
> +	const unsigned int width = is64 ? 64 : 32;
> +
> +	imm &= width - 1;
> +	emit_bitfield(ctx, is64, rd, rd, imm, width - 1, A64_UBFM);
>  }
> 
>  static void
>  emit_asr(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
>  {
> -	emit_bitfield(ctx, is64, rd, rd, imm, is64 ? 63 : 31, A64_SBFM);
> +	const unsigned int width = is64 ? 64 : 32;
> +
> +	imm &= width - 1;
> +	emit_bitfield(ctx, is64, rd, rd, imm, width - 1, A64_SBFM);
>  }
> 
>  #define A64_AND 0
> --
> 2.53.0