linux-kernel - Re: Regression [Was: Boot hang with stack protector on x86

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Date:	Sat, 23 Feb 2008 07:18:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	James Morris <jmorris@...ei.org>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Regression [Was: Boot hang with stack protector on x86_64]


James,

could you try the fix below ontop of x86.git#testing, does it solve your 
boot hang?

	Ingo

--------------->
Subject: x86: stackprotector fix: do not zap %gs
From: Ingo Molnar <mingo@...e.hu>
Date: Sat Feb 23 07:06:55 CET 2008

pda_init() puts 0 into %gs - that's wrong because any %gs access will 
fault from now on and we already have a dummy PDA set up that can be 
accessed just fine.

This normally does not matter because almost nothing accesses %gs this 
early ... but the stackprotector now does to read the canary ...

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/setup64.c |    2 --
 1 file changed, 2 deletions(-)

Index: linux-x86.q/arch/x86/kernel/setup64.c
===================================================================
--- linux-x86.q.orig/arch/x86/kernel/setup64.c
+++ linux-x86.q/arch/x86/kernel/setup64.c
@@ -165,8 +165,6 @@ void pda_init(int cpu)
 { 
 	struct x8664_pda *pda = cpu_pda(cpu);
 
-	/* Setup up data that may be needed in __get_free_pages early */
-	asm volatile("movl %0,%%fs ; movl %0,%%gs" :: "r" (0)); 
 	/* Memory clobbers used to order PDA accessed */
 	mb();
 	wrmsrl(MSR_GS_BASE, pda);
--
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