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s390/bpf: Fix 64-bit subtraction of the -0x80000000 constant

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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: 0546231057 ("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>
This commit is contained in:
Ilya Leoshkevich 2021-09-07 13:41:16 +02:00 committed by Vasily Gorbik
parent 1511df6f5e
commit 6e61dc9da0
1 changed files with 7 additions and 2 deletions
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9
arch/s390/net/bpf_jit_comp.c
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@ -794,8 +794,13 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
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