This is a note to let you know that I've just added the patch titled
s390/bpf: Fix 64-bit subtraction of the -0x80000000 constant
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
s390-bpf-fix-64-bit-subtraction-of-the-0x80000000-constant.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6e61dc9da0b7a0d91d57c2e20b5ea4fd2d4e7e53 Mon Sep 17 00:00:00 2001
From: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
Date: Tue, 7 Sep 2021 13:41:16 +0200
Subject: s390/bpf: Fix 64-bit subtraction of the -0x80000000 constant
From: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxx>
Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Reviewed-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/net/bpf_jit_comp.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -625,8 +625,13 @@ static noinline int bpf_jit_insn(struct
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
Patches currently in stable-queue which might be from iii@xxxxxxxxxxxxx are
queue-4.9/s390-bpf-fix-64-bit-subtraction-of-the-0x80000000-constant.patch
