linux-kernel - [PATCH 3/3] arm64/syscalls: Move address limit check in loop

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Message-Id: <20170719175900.124074-3-thgarnie@google.com>
Date:   Wed, 19 Jul 2017 10:59:00 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Russell King <linux@...linux.org.uk>,
        Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Pratyush Anand <panand@...hat.com>, leonard.crestez@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: [PATCH 3/3] arm64/syscalls: Move address limit check in loop

The original bug was reported on arm but I am fixing arm64 too because
it has a similar code pattern.

The work pending loop can call set_fs after addr_limit_user_check
removed the _TIF_FSCHECK flag. To prevent the infinite loop, move the
addr_limit_user_check call at the beginning of the loop.

Fixes: cf7de27ab351 ("arm64/syscalls: Check address limit on user-mode return")
Reported-by: Leonard Crestez <leonard.crestez@....com>
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/arm64/kernel/signal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index e3e3293d1123..8e2705983e1d 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -751,10 +751,10 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 	 */
 	trace_hardirqs_off();
 
-	/* Check valid user FS if needed */
-	addr_limit_user_check();
-
 	do {
+		/* Check valid user FS if needed */
+		addr_limit_user_check();
+
 		if (thread_flags & _TIF_NEED_RESCHED) {
 			schedule();
 		} else {
-- 
2.14.0.rc0.284.gd933b75aa4-goog