[PATCH 4.9 01/26] s390/bpf: Fix optimizing out zero-extensions

Greg Kroah-Hartman
2021-09-24T12:46:18Z

From: Ilya Leoshkevich <iii@linux.ibm.com>

commit db7bee653859ef7179be933e7d1384644f795f26 upstream.

Currently the JIT completely removes things like `reg32 += 0`,
however, the BPF_ALU semantics requires the target register to be
zero-extended in such cases.

Fix by optimizing out only the arithmetic operation, but not the
subsequent zero-extension.

Reported-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/net/bpf_jit_comp.c | 50 ++++++++++++++++++++++---------------------
1 file changed, 26 insertions(+), 24 deletions(-)

--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -591,10 +591,10 @@ static noinline int bpf_jit_insn(struct
EMIT4(0xb9080000, dst_reg, src_reg);
break;
case BPF_ALU | BPF_ADD | BPF_K: /* dst = (u32) dst + (u32) imm */
- if (!imm)
- break;
- /* alfi %dst,imm */
- EMIT6_IMM(0xc20b0000, dst_reg, imm);
+ if (imm != 0) {
+ /* alfi %dst,imm */
+ EMIT6_IMM(0xc20b0000, dst_reg, imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_ADD | BPF_K: /* dst = dst + imm */
@@ -616,10 +616,10 @@ static noinline int bpf_jit_insn(struct
EMIT4(0xb9090000, dst_reg, src_reg);
break;
case BPF_ALU | BPF_SUB | BPF_K: /* dst = (u32) dst - (u32) imm */
- if (!imm)
- break;
- /* alfi %dst,-imm */
- EMIT6_IMM(0xc20b0000, dst_reg, -imm);
+ if (imm != 0) {
+ /* alfi %dst,-imm */
+ EMIT6_IMM(0xc20b0000, dst_reg, -imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_SUB | BPF_K: /* dst = dst - imm */
@@ -646,10 +646,10 @@ static noinline int bpf_jit_insn(struct
EMIT4(0xb90c0000, dst_reg, src_reg);
break;
case BPF_ALU | BPF_MUL | BPF_K: /* dst = (u32) dst * (u32) imm */
- if (imm == 1)
- break;
- /* msfi %r5,imm */
- EMIT6_IMM(0xc2010000, dst_reg, imm);
+ if (imm != 1) {
+ /* msfi %r5,imm */
+ EMIT6_IMM(0xc2010000, dst_reg, imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_MUL | BPF_K: /* dst = dst * imm */
@@ -710,6 +710,8 @@ static noinline int bpf_jit_insn(struct
if (BPF_OP(insn->code) == BPF_MOD)
/* lhgi %dst,0 */
EMIT4_IMM(0xa7090000, dst_reg, 0);
+ else
+ EMIT_ZERO(dst_reg);
break;
}
/* lhi %w0,0 */
@@ -802,10 +804,10 @@ static noinline int bpf_jit_insn(struct
EMIT4(0xb9820000, dst_reg, src_reg);
break;
case BPF_ALU | BPF_XOR | BPF_K: /* dst = (u32) dst ^ (u32) imm */
- if (!imm)
- break;
- /* xilf %dst,imm */
- EMIT6_IMM(0xc0070000, dst_reg, imm);
+ if (imm != 0) {
+ /* xilf %dst,imm */
+ EMIT6_IMM(0xc0070000, dst_reg, imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_XOR | BPF_K: /* dst = dst ^ imm */
@@ -826,10 +828,10 @@ static noinline int bpf_jit_insn(struct
EMIT6_DISP_LH(0xeb000000, 0x000d, dst_reg, dst_reg, src_reg, 0);
break;
case BPF_ALU | BPF_LSH | BPF_K: /* dst = (u32) dst << (u32) imm */
- if (imm == 0)
- break;
- /* sll %dst,imm(%r0) */
- EMIT4_DISP(0x89000000, dst_reg, REG_0, imm);
+ if (imm != 0) {
+ /* sll %dst,imm(%r0) */
+ EMIT4_DISP(0x89000000, dst_reg, REG_0, imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_LSH | BPF_K: /* dst = dst << imm */
@@ -851,10 +853,10 @@ static noinline int bpf_jit_insn(struct
EMIT6_DISP_LH(0xeb000000, 0x000c, dst_reg, dst_reg, src_reg, 0);
break;
case BPF_ALU | BPF_RSH | BPF_K: /* dst = (u32) dst >> (u32) imm */
- if (imm == 0)
- break;
- /* srl %dst,imm(%r0) */
- EMIT4_DISP(0x88000000, dst_reg, REG_0, imm);
+ if (imm != 0) {
+ /* srl %dst,imm(%r0) */
+ EMIT4_DISP(0x88000000, dst_reg, REG_0, imm);
+ }
EMIT_ZERO(dst_reg);
break;
case BPF_ALU64 | BPF_RSH | BPF_K: /* dst = dst >> imm */