s390: fix br_r1_trampoline for machines without exrl

commit 26f843848bae973817b3587780ce6b7b0200d3e4 upstream.

For machines without the exrl instruction the BFP jit generates
code that uses an "br %r1" instruction located in the lowcore page.
Unfortunately there is a cut & paste error that puts an additional
"larl %r1,.+14" instruction in the code that clobbers the branch
target address in %r1. Remove the larl instruction.

Cc: <stable@vger.kernel.org> # v4.17+
Fixes: de5cb6eb51 ("s390: use expoline thunks in the BPF JIT")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.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 45f1ea11712862da910471ab8d1afcae65efa977..6b1474fa99ab3f98f68227fa97fc4d0768445ac3 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -518,8 +518,6 @@ static void bpf_jit_epilogue(struct bpf_jit *jit)
                        /* br %r1 */
                        _EMIT2(0x07f1);
                } else {
-                       /* larl %r1,.+14 */
-                       EMIT6_PCREL_RILB(0xc0000000, REG_1, jit->prg + 14);
                        /* ex 0,S390_lowcore.br_r1_tampoline */
                        EMIT4_DISP(0x44000000, REG_0, REG_0,
                                   offsetof(struct lowcore, br_r1_trampoline));