Commit 33a9081e authored Aug 06, 2018 by Martin Schwidefsky Committed by Greg Kroah-Hartman Sep 05, 2018

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>

parent ba064e81

arch/s390/net/bpf_jit_comp.c

+0 −2

Original line number	Original line	Diff line number	Diff line
	@@ -517,8 +517,6 @@ static void bpf_jit_epilogue(struct bpf_jit *jit)
	/* br %r1 */		/* br %r1 */
	_EMIT2(0x07f1);		_EMIT2(0x07f1);
	} else {		} else {
	/* larl %r1,.+14 */
	EMIT6_PCREL_RILB(0xc0000000, REG_1, jit->prg + 14);
	/* ex 0,S390_lowcore.br_r1_tampoline */		/* ex 0,S390_lowcore.br_r1_tampoline */
	EMIT4_DISP(0x44000000, REG_0, REG_0,		EMIT4_DISP(0x44000000, REG_0, REG_0,
	offsetof(struct lowcore, br_r1_trampoline));		offsetof(struct lowcore, br_r1_trampoline));