[PATCH bpf-next v3 2/8] s390/bpf: Add expoline to tail calls

Ilya Leoshkevich
2023-01-29T19:05:38Z

All the indirect jumps in the eBPF JIT already use expolines, except
for the tail call one.

Fixes: de5cb6eb514e ("s390: use expoline thunks in the BPF JIT")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
arch/s390/net/bpf_jit_comp.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index eb1a78c0e6a8..8400a06c926e 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1393,8 +1393,16 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
/* lg %r1,bpf_func(%r1) */
EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, REG_1, REG_0,
offsetof(struct bpf_prog, bpf_func));
- /* bc 0xf,tail_call_start(%r1) */
- _EMIT4(0x47f01000 + jit->tail_call_start);
+ if (nospec_uses_trampoline()) {
+ jit->seen |= SEEN_FUNC;
+ /* aghi %r1,tail_call_start */
+ EMIT4_IMM(0xa70b0000, REG_1, jit->tail_call_start);
+ /* brcl 0xf,__s390_indirect_jump_r1 */
+ EMIT6_PCREL_RILC(0xc0040000, 0xf, jit->r1_thunk_ip);
+ } else {
+ /* bc 0xf,tail_call_start(%r1) */
+ _EMIT4(0x47f01000 + jit->tail_call_start);
+ }
/* out: */
if (jit->prg_buf) {
*(u16 *)(jit->prg_buf + patch_1_clrj + 2) =
--
2.39.1