s390/bpf: clear correct BPF accumulator register

Currently we assumed the following BPF to eBPF register mapping:

 - BPF_REG_A -> BPF_REG_7
 - BPF_REG_X -> BPF_REG_8

Unfortunately this mapping is wrong. The correct mapping is:

 - BPF_REG_A -> BPF_REG_0
 - BPF_REG_X -> BPF_REG_7

So clear the correct registers and use the BPF_REG_A and BPF_REG_X
macros instead of BPF_REG_0/7.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
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>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index fee782acc2ee51f6a3aae4b28152ec76981c8350..8d2e5165865f2c27b50fe8b1c6845de45666698a 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -448,13 +448,13 @@ static void bpf_jit_prologue(struct bpf_jit *jit)
                EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
                              BPF_REG_1, offsetof(struct sk_buff, data));
        }
-       /* BPF compatibility: clear A (%b7) and X (%b8) registers */
-       if (REG_SEEN(BPF_REG_7))
-               /* lghi %b7,0 */
-               EMIT4_IMM(0xa7090000, BPF_REG_7, 0);
-       if (REG_SEEN(BPF_REG_8))
-               /* lghi %b8,0 */
-               EMIT4_IMM(0xa7090000, BPF_REG_8, 0);
+       /* BPF compatibility: clear A (%b0) and X (%b7) registers */
+       if (REG_SEEN(BPF_REG_A))
+               /* lghi %ba,0 */
+               EMIT4_IMM(0xa7090000, BPF_REG_A, 0);
+       if (REG_SEEN(BPF_REG_X))
+               /* lghi %bx,0 */
+               EMIT4_IMM(0xa7090000, BPF_REG_X, 0);
 }
 
 /*