[SRU Bionic/Focal] powerpc/bpf: Fix BPF_MOD when imm == 1

[Thadeu Lima de Souza Cascardo]

From: "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1948351

Only ignore the operation if dividing by 1.

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>
Tested-by: Johan Almbladh <johan.almbladh at anyfinetworks.com>
Reviewed-by: Christophe Leroy <christophe.leroy at csgroup.eu>
Acked-by: Song Liu <songliubraving at fb.com>
Acked-by: Johan Almbladh <johan.almbladh at anyfinetworks.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Link: https://lore.kernel.org/r/c674ca18c3046885602caebb326213731c675d06.1633464148.git.naveen.n.rao@linux.vnet.ibm.com

(backported from commit 8bbc9d822421d9ac8ff9ed26a3713c9afc69d6c8)
[cascardo: use PPC_LI instead of EMIT(PPC_RAW_LI)]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 arch/powerpc/net/bpf_jit_comp64.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 20bfd753bcba..81e6279c9874 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -408,8 +408,14 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 		case BPF_ALU64 | BPF_DIV | BPF_K: /* dst /= imm */
 			if (imm == 0)
 				return -EINVAL;
-			else if (imm == 1)
-				goto bpf_alu32_trunc;
+			if (imm == 1) {
+				if (BPF_OP(code) == BPF_DIV) {
+					goto bpf_alu32_trunc;
+				} else {
+					PPC_LI(dst_reg, 0);
+					break;
+				}
+			}
 
 			PPC_LI32(b2p[TMP_REG_1], imm);
 			switch (BPF_CLASS(code)) {
-- 
2.32.0