powerpc/bpf: Fix BPF_SUB when imm == 0x80000000

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@linux.vnet.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fold in fix from Naveen to use imm <= 32768]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/fc4b1276eb10761fd7ce0814c8dd089da2815251.1633464148.git.naveen.n.rao@linux.vnet.ibm.com

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index d67f6d62e2e1ffd76cb08bcf72611d2f3c566f9a..2ea1c3f6e287d4ecd877ce83d15bdaa7d14ac339 100644 (file)
--- 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 */