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@vger.kernel.org Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com --- 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; }

/*