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>
b035b60ded