Commit 54ac8339 authored Sep 07, 2021 by Ilya Leoshkevich Committed by Greg Kroah-Hartman Sep 22, 2021

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: 05462310 ("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>

parent a5fc4800

arch/s390/net/bpf_jit_comp.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -603,8 +603,13 @@ 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;
		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