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From: Ammar Faizi <[email protected]>
To: Borislav Petkov <[email protected]>, Thomas Gleixner <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Dave Hansen <[email protected]>,
	Greg Kroah-Hartman <[email protected]>,
	"H. Peter Anvin" <[email protected]>, Ingo Molnar <[email protected]>,
	Tony Luck <[email protected]>,
	Yazen Ghannam <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected], [email protected],
	David Laight <[email protected]>,
	Jiri Hladky <[email protected]>
Subject: [PATCH v5 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`
Date: Thu, 10 Mar 2022 08:53:05 +0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

The asm constraint does not reflect that the asm statement can modify
the value of @loops. But the asm statement in delay_loop() does modify
the @loops.

Specifiying the wrong constraint may lead to undefined behavior, it may
clobber random stuff (e.g. local variable, important temporary value in
regs, etc.).

Fix this by changing the constraint from "a" (as an input) to "+a" (as
an input and output).

Cc: David Laight <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Jiri Hladky <[email protected]>
Cc: [email protected] # v2.6.27+
Fixes: e01b70ef3eb ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function")
Signed-off-by: Ammar Faizi <[email protected]>
---
 arch/x86/lib/delay.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index 65d15df6212d..0e65d00e2339 100644
--- a/arch/x86/lib/delay.c
+++ b/arch/x86/lib/delay.c
@@ -54,8 +54,8 @@ static void delay_loop(u64 __loops)
 		"	jnz 2b		\n"
 		"3:	dec %0		\n"
 
-		: /* we don't need output */
-		:"a" (loops)
+		: "+a" (loops)
+		:
 	);
 }
 
-- 
2.32.0


  reply	other threads:[~2022-03-10  1:53 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-10  1:53 [PATCH v5 0/2] Two x86 fixes Ammar Faizi
2022-03-10  1:53 ` Ammar Faizi [this message]
2022-03-27 21:38   ` [PATCH v5 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Borislav Petkov
2022-03-28  4:16     ` Ammar Faizi
2022-03-28  4:29     ` Ammar Faizi
2022-03-28  7:56       ` Borislav Petkov
2022-03-10  1:53 ` [PATCH v5 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails Ammar Faizi
2022-03-27 22:52   ` Borislav Petkov
2022-03-28  4:12     ` Ammar Faizi
2022-03-28  8:05       ` Borislav Petkov
2022-03-17  8:19 ` [PATCH v5 0/2] Two x86 fixes Ammar Faizi
2022-03-17  9:27   ` Borislav Petkov
2022-03-17  9:50     ` Ammar Faizi

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