[PATCH bpf-next 2/3] riscv, bpf: Fix support for BPF_MOVSX in RV32 JIT

[Kuan-Wei Chiu]

The current rv32 bpf jit compiler incorrectly treats BPF_MOVSX as a
standard zero-extended move operation. The bpf instruction set allows
sign-extension moves by reusing the BPF_MOV opcode with the instruction
offset set to 8, 16, or 32.

Update the bpf_jit_emit_insn() function to check the offset field for
both ALU and ALU64 MOV operations. If the offset is non-zero, emit the
correct slli and srai instructions to perform the sign extension.

Before this patch:
[   19.549705] test_bpf: #82 ALU_MOVSX | BPF_B jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
[   19.551354] test_bpf: #83 ALU_MOVSX | BPF_H jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
[   19.552576] test_bpf: #84 ALU64_MOVSX | BPF_B jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
[   19.553542] test_bpf: #85 ALU64_MOVSX | BPF_H jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
[   19.554807] test_bpf: #86 ALU64_MOVSX | BPF_W jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)

After this patch:
[   17.931172] test_bpf: #82 ALU_MOVSX | BPF_B jited:1 125 PASS
[   17.932198] test_bpf: #83 ALU_MOVSX | BPF_H jited:1 124 PASS
[   17.933039] test_bpf: #84 ALU64_MOVSX | BPF_B jited:1 124 PASS
[   17.933918] test_bpf: #85 ALU64_MOVSX | BPF_H jited:1 124 PASS
[   17.934751] test_bpf: #86 ALU64_MOVSX | BPF_W jited:1 122 PASS

Signed-off-by: Kuan-Wei Chiu <visitorckw at gmail.com>
---
 arch/riscv/net/bpf_jit_comp32.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/riscv/net/bpf_jit_comp32.c b/arch/riscv/net/bpf_jit_comp32.c
index 7396899ea276..f8509950fed4 100644
--- a/arch/riscv/net/bpf_jit_comp32.c
+++ b/arch/riscv/net/bpf_jit_comp32.c
@@ -974,6 +974,24 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 
 	switch (code) {
 	case BPF_ALU64 | BPF_MOV | BPF_X:
+		if (insn->off != 0) {
+			const s8 *rd = bpf_get_reg64(dst, tmp1, ctx);
+			const s8 *rs = bpf_get_reg64(src, tmp2, ctx);
+
+			if (insn->off == 8) {
+				emit(rv_slli(lo(rd), lo(rs), 24), ctx);
+				emit(rv_srai(lo(rd), lo(rd), 24), ctx);
+			} else if (insn->off == 16) {
+				emit(rv_slli(lo(rd), lo(rs), 16), ctx);
+				emit(rv_srai(lo(rd), lo(rd), 16), ctx);
+			} else {
+				emit(rv_addi(lo(rd), lo(rs), 0), ctx);
+			}
+			emit(rv_srai(hi(rd), lo(rd), 31), ctx);
+			bpf_put_reg64(dst, rd, ctx);
+			break;
+		}
+		fallthrough;
 
 	case BPF_ALU64 | BPF_ADD | BPF_X:
 	case BPF_ALU64 | BPF_ADD | BPF_K:
@@ -1024,6 +1042,20 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			emit_zext64(dst, ctx);
 			break;
 		}
+		if (insn->off != 0) {
+			const s8 *rd = bpf_get_reg32(dst, tmp1, ctx);
+			const s8 *rs = bpf_get_reg32(src, tmp2, ctx);
+
+			if (insn->off == 8) {
+				emit(rv_slli(lo(rd), lo(rs), 24), ctx);
+				emit(rv_srai(lo(rd), lo(rd), 24), ctx);
+			} else if (insn->off == 16) {
+				emit(rv_slli(lo(rd), lo(rs), 16), ctx);
+				emit(rv_srai(lo(rd), lo(rd), 16), ctx);
+			}
+			bpf_put_reg32(dst, rd, ctx);
+			break;
+		}
 		fallthrough;
 
 	case BPF_ALU | BPF_ADD | BPF_X:
-- 
2.54.0.545.g6539524ca2-goog