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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From b035b60ded132592055c0f9bd1cc280259c7de4b Mon Sep 17 00:00:00 2001
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Thu, 21 May 2015 15:39:31 +0200
Subject: s390/bpf: Fix backward jumps

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

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.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -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 holzheu@linux.vnet.ibm.com are

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