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From:   Matteo Croce <mcroce@redhat.com>
To:     x86@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH] x86/traps: print faulty addresses on stack overflow
Date:   Mon,  1 Apr 2019 02:03:27 +0200
Message-Id: <20190401000327.26742-1-mcroce@redhat.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Since commit ad67b74d2469d9b8 ("printk: hash addresses printed with %p"),
when a stack overflow happens "____ptrval____" is printed instead of the
real addresses:

    BUG: stack guard page was hit at (____ptrval____) (stack is (____ptrval____)..(____ptrval____))

Even if leaking kernel layout information is usually a bad thing, probably
the system needs to be rebooted anyway past this point, so force the
address print as the obfuscation makes the error message useless.

Signed-off-by: Matteo Croce <mcroce@redhat.com>
---
 arch/x86/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d26f9e9c3d83..0d3695334dfd 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -301,7 +301,7 @@ __visible void __noreturn handle_stack_overflow(const char *message,
 						struct pt_regs *regs,
 						unsigned long fault_address)
 {
-	printk(KERN_EMERG "BUG: stack guard page was hit at %p (stack is %p..%p)\n",
+	printk(KERN_EMERG "BUG: stack guard page was hit at %px (stack is %px..%px)\n",
 		 (void *)fault_address, current->stack,
 		 (char *)current->stack + THREAD_SIZE - 1);
 	die(message, regs, 0);
-- 
2.20.1