selftests/rseq: Fix: Fail thread registration when CONFIG_RSEQ=n

When linking the selftests against a libc which does not handle rseq
registration (before 2.35),  rseq thread registration silently succeed
even with CONFIG_RSEQ=n because it erroneously thinks that libc is
handling rseq registration.

This is caused by setting the rseq ownership flag only after the
rseq_available() check. It should rather be set before the
rseq_available() check.

Set the rseq_size to 0 (error value) immediately after the
rseq_available() check fails rather than in the thread registration
functions.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-2-mathieu.desnoyers@efficios.com

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4177f95..376a73f 100644 (file)
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -119,9 +119,11 @@ void rseq_init(void)
                rseq_flags = *libc_rseq_flags_p;
                return;
        }
-       if (!rseq_available())
-               return;
        rseq_ownership = 1;
+       if (!rseq_available()) {
+               rseq_size = 0;
+               return;
+       }
        rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
        rseq_size = sizeof(struct rseq_abi);
        rseq_flags = 0;