[PATCH bpf-next 5/5] bpf, x86: Add unconditional byte swap to the i386 JIT

[Nicholas Dudar <main.kalliope@gmail.com>]

The i386 JIT rejects unconditional BPF byte-swap instructions, which use
BPF_ALU64 | BPF_END.

Route them through the existing big-endian conversion emitter. On
little-endian i386, it provides the same 16-, 32- and 64-bit byte swaps.
The verifier treats sub-64-bit BPF_END results as 32-bit definitions and
inserts zero extension where the upper word is used. The emitter clears
that word itself when verifier_zext is disabled.

Assisted-by: Codex:gpt-6
Signed-off-by: Nicholas Dudar <main.kalliope@gmail.com>
---
 arch/x86/net/bpf_jit_comp32.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 2d8a3a961e91..bdba05b72ef3 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -2037,6 +2037,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			break;
 		/* dst = htobe(dst) */
 		case BPF_ALU | BPF_END | BPF_FROM_BE:
+		/* dst = bswap(dst) */
+		case BPF_ALU64 | BPF_END | BPF_FROM_LE:
 			emit_ia32_to_be_r64(dst, imm32, dstk, &prog,
 					    bpf_prog->aux);
 			break;