s390/bpf: Fix branch shortening during codegen pass

commit 1511df6f5e9ef32826f20db2ee81f8527154dc14 upstream.

EMIT6_PCREL() macro assumes that the previous pass generated 6 bytes
of code, which is not the case if branch shortening took place. Fix by
using jit->prg, like all the other EMIT6_PCREL_*() macros.

Reported-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Fixes: 4e9b4a6883dd ("s390/bpf: Use relative long branches")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index cba6e98..8d9047d 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -248,8 +248,7 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 
 #define EMIT6_PCREL(op1, op2, b1, b2, i, off, mask)            \
 ({                                                             \
-       /* Branch instruction needs 6 bytes */                  \
-       int rel = (addrs[(i) + (off) + 1] - (addrs[(i) + 1] - 6)) / 2;\
+       int rel = (addrs[(i) + (off) + 1] - jit->prg) / 2;      \
        _EMIT6((op1) | reg(b1, b2) << 16 | (rel & 0xffff), (op2) | (mask));\
        REG_SET_SEEN(b1);                                       \
        REG_SET_SEEN(b2);                                       \