bpf, arm64: Support sign-extension mov instructions

Add JIT support for BPF sign-extension mov instructions with arm64
SXTB/SXTH/SXTW instructions.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Florent Revest <revest@chromium.org>
Acked-by: Florent Revest <revest@chromium.org>
Link: https://lore.kernel.org/bpf/20230815154158.717901-4-xukuohai@huaweicloud.com

Author: Xu Kuohai

arch/arm64/net/bpf_jit.h

@@ -192,6 +192,11 @@
 #define A64_UXTH(sf, Rd, Rn) A64_UBFM(sf, Rd, Rn, 0, 15)
 #define A64_UXTW(sf, Rd, Rn) A64_UBFM(sf, Rd, Rn, 0, 31)
 
+/* Sign extend */
+#define A64_SXTB(sf, Rd, Rn) A64_SBFM(sf, Rd, Rn, 0, 7)
+#define A64_SXTH(sf, Rd, Rn) A64_SBFM(sf, Rd, Rn, 0, 15)
+#define A64_SXTW(sf, Rd, Rn) A64_SBFM(sf, Rd, Rn, 0, 31)
+
 /* Move wide (immediate) */
 #define A64_MOVEW(sf, Rd, imm16, shift, type) \
 	aarch64_insn_gen_movewide(Rd, imm16, shift, \

arch/arm64/net/bpf_jit_comp.c

@@ -786,7 +786,20 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 	/* dst = src */
 	case BPF_ALU | BPF_MOV | BPF_X:
 	case BPF_ALU64 | BPF_MOV | BPF_X:
-		emit(A64_MOV(is64, dst, src), ctx);
+		switch (insn->off) {
+		case 0:
+			emit(A64_MOV(is64, dst, src), ctx);
+			break;
+		case 8:
+			emit(A64_SXTB(is64, dst, src), ctx);
+			break;
+		case 16:
+			emit(A64_SXTH(is64, dst, src), ctx);
+			break;
+		case 32:
+			emit(A64_SXTW(is64, dst, src), ctx);
+			break;
+		}
 		break;
 	/* dst = dst OP src */
 	case BPF_ALU | BPF_ADD | BPF_X: