[PATCH v2 04/10] powerpc/bpf: Fix BPF_SUB when imm == 0x80000000

[Naveen N. Rao]

We aren't handling subtraction involving an immediate value of
0x80000000 properly. Fix the same.

Fixes: 156d0e290e969c ("powerpc/ebpf/jit: Implement JIT compiler for extended BPF")
Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
---
Changelog:
- Split up BPF_ADD and BPF_SUB cases per Christophe's comments

 arch/powerpc/net/bpf_jit_comp64.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index d67f6d62e2e1ff..6626e6c17d4ed2 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -330,18 +330,25 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 			EMIT(PPC_RAW_SUB(dst_reg, dst_reg, src_reg));
 			goto bpf_alu32_trunc;
 		case BPF_ALU | BPF_ADD | BPF_K: /* (u32) dst += (u32) imm */
-		case BPF_ALU | BPF_SUB | BPF_K: /* (u32) dst -= (u32) imm */
 		case BPF_ALU64 | BPF_ADD | BPF_K: /* dst += imm */
+			if (!imm) {
+				goto bpf_alu32_trunc;
+			} else if (imm >= -32768 && imm < 32768) {
+				EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(imm)));
+			} else {
+				PPC_LI32(b2p[TMP_REG_1], imm);
+				EMIT(PPC_RAW_ADD(dst_reg, dst_reg, b2p[TMP_REG_1]));
+			}
+			goto bpf_alu32_trunc;
+		case BPF_ALU | BPF_SUB | BPF_K: /* (u32) dst -= (u32) imm */
 		case BPF_ALU64 | BPF_SUB | BPF_K: /* dst -= imm */
-			if (BPF_OP(code) == BPF_SUB)
-				imm = -imm;
-			if (imm) {
-				if (imm >= -32768 && imm < 32768)
-					EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(imm)));
-				else {
-					PPC_LI32(b2p[TMP_REG_1], imm);
-					EMIT(PPC_RAW_ADD(dst_reg, dst_reg, b2p[TMP_REG_1]));
-				}
+			if (!imm) {
+				goto bpf_alu32_trunc;
+			} else if (imm > -32768 && imm < 32768) {
+				EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(-imm)));
+			} else {
+				PPC_LI32(b2p[TMP_REG_1], imm);
+				EMIT(PPC_RAW_SUB(dst_reg, dst_reg, b2p[TMP_REG_1]));
 			}
 			goto bpf_alu32_trunc;
 		case BPF_ALU | BPF_MUL | BPF_X: /* (u32) dst *= (u32) src */
-- 
2.33.0