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s390/bpf: Fix backward jumps 

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.

Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Michael Holzheu 2015-05-21 15:39:31 +02:00 committed by Martin Schwidefsky
parent aefbef10e3
commit b035b60ded
1 changed files with 1 additions and 1 deletions
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2
arch/s390/net/bpf_jit_comp.c
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@ -250,7 +250,7 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
({ \
/* 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); \
})