Commit 7ded842b356d ("s390/bpf: Fix bpf_plt pointer arithmetic") has
accidentally removed the critical piece of commit c730fce7c70c
("s390/bpf: Fix bpf_arch_text_poke() with new_addr == NULL"), causing
intermittent kernel panics in e.g. perf's on_switch() prog to reappear.
Restore the fix and add a comment.
Fixes: 7ded842b356d ("s390/bpf: Fix bpf_plt pointer arithmetic")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
arch/s390/net/bpf_jit_comp.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 8bb738f1b1b6..bb17efe29d65 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -576,7 +576,15 @@ static void bpf_jit_plt(struct bpf_plt *plt, void *ret, void *target)
{
memcpy(plt, &bpf_plt, sizeof(*plt));
plt->ret = ret;
- plt->target = target;
+ /*
+ * (target == NULL) implies that the branch to this PLT entry was
+ * patched and became a no-op. However, some CPU could have jumped
+ * to this PLT entry before patching and may be still executing it.
+ *
+ * Since the intention in this case is to make the PLT entry a no-op,
+ * make the target point to the return label instead of NULL.
+ */
+ plt->target = target ?: ret;
}
/*
--
2.50.1
