linux-kernel - [PATCH 01/30] selftests/rseq: Fix: Fail thread registration when CONFIG

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Date:   Tue, 22 Nov 2022 15:39:03 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
        Florian Weimer <fw@...eb.enyo.de>, David.Laight@...LAB.COM,
        carlos@...hat.com, Peter Oskolkov <posk@...k.io>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH 01/30] 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@...icios.com>
---
 tools/testing/selftests/rseq/rseq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4177f9507bbe..376a73f1ac41 100644
--- 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;
-- 
2.25.1