Patch "s390/bpf: Fix backward jumps" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

s390/bpf: Fix backward jumps

to the 4.1-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-backward-jumps.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Holzheu <[email protected]>
Date: Thu, 21 May 2015 15:39:31 +0200
Subject: s390/bpf: Fix backward jumps

From: Michael Holzheu <[email protected]>

commit b035b60ded132592055c0f9bd1cc280259c7de4b upstream.

Currently all backward jumps crash for JITed s390x eBPF programs with an illegal instruction program check and kernel panic. Because for negative values the opcode of the jump instruction is overriden by the negative branch offset an illegal instruction is generated by the JIT:

 000003ff802da378: c01100000002   lgfi    %r1,2
 000003ff802da37e: fffffff52065   unknown <-- illegal instruction
 000003ff802da384: b904002e       lgr     %r2,%r14

So fix this and mask the offset in order not to damage the opcode.

---
 arch/s390/net/bpf_jit_comp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -227,7 +227,7 @@ static inline void reg_set_seen(struct b
 ({								\
 	/* Branch instruction needs 6 bytes */			\
 	int rel = (addrs[i + off + 1] - (addrs[i + 1] - 6)) / 2;\
-	_EMIT6(op1 | reg(b1, b2) << 16 | rel, op2 | mask);	\
+	_EMIT6(op1 | reg(b1, b2) << 16 | (rel & 0xffff), op2 | mask);	\
 	REG_SET_SEEN(b1);					\
 	REG_SET_SEEN(b2);					\
 })

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/s390-kdump-fix-regset_vx_low-vector-register-elf-notes.patch queue-4.1/s390-bpf-fix-backward-jumps.patch