s390/bpf: reduce maximum program size to 64 KB

commit 0fa963553a5c28d8f8aabd8878326d3f782045fc upstream.

The s390 BFP compiler currently uses relative branch instructions
that only support jumps up to 64 KB. Examples are "j", "jnz", "cgrj",
etc.  Currently the maximum size of s390 BPF programs is set
to 0x7ffff.  If branches over 64 KB are generated the, kernel can
crash due to incorrect code.

So fix this an reduce the maximum size to 64 KB. Programs larger than
that will be interpreted.

Fixes: ce2b6ad9c185 ("s390/bpf: increase BPF_SIZE_MAX")
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>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index fe607c8d25d236308f16485323b002e31026e83b..0e2919dd8df368d8362570e138771139a9073b17 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -45,7 +45,7 @@ struct bpf_jit {
        int labels[1];          /* Labels for local jumps */
 };
 
-#define BPF_SIZE_MAX   0x7ffff /* Max size for program (20 bit signed displ) */
+#define BPF_SIZE_MAX   0xffff  /* Max size for program (16 bit branches) */
 
 #define SEEN_SKB       1       /* skb access */
 #define SEEN_MEM       2       /* use mem[] for temporary storage */