s390/bpf: Fix 64-bit subtraction of the -0x80000000 constant
commit 6e61dc9da0b7a0d91d57c2e20b5ea4fd2d4e7e53 upstream.
The JIT uses agfi for subtracting constants, but -(-0x80000000) cannot
be represented as a 32-bit signed binary integer. Fix by using algfi in
this particular case.
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>
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 9ae86f6..2d29966 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -603,8 +603,13 @@
case BPF_ALU64 | BPF_SUB | BPF_K: /* dst = dst - imm */
if (!imm)
break;
- /* agfi %dst,-imm */
- EMIT6_IMM(0xc2080000, dst_reg, -imm);
+ if (imm == -0x80000000) {
+ /* algfi %dst,0x80000000 */
+ EMIT6_IMM(0xc20a0000, dst_reg, 0x80000000);
+ } else {
+ /* agfi %dst,-imm */
+ EMIT6_IMM(0xc2080000, dst_reg, -imm);
+ }
break;
/*
* BPF_MUL
