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

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Date:	Mon, 25 Feb 2008 09:53:37 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Ingo Molnar <mingo@...e.hu>
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]

On Sat, 23 Feb 2008, Ingo Molnar wrote:

> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > could you try the fix below ontop of x86.git#testing, does it solve 
> > your boot hang?
> 
> find below another fix that is somewhat better as it does not affect the 
> native kernel and !PARAVIRT.

This works.

> 
> btw., this also explains why this bug wasnt reported sooner against 
> x86.git#testing: people done normally use PARAVIRT on 64-bit yet.
> (there is no 64-bit host support)
> 
> 	Ingo
> 
> ---------------->
> Subject: x86: stackprotector & PARAVIRT fix
> From: Ingo Molnar <mingo@...e.hu>
> Date: Sat Feb 23 07:06:55 CET 2008
> 
> on paravirt enabled 64-bit kernels the paravirt ops do function
> calls themselves - which is bad with the stackprotector - for
> example pda_init() loads 0 into %gs and then does MSR_GS_BASE
> write (which modifies gs.base) - but that MSR write is a function
> call on paravirt, which with stackprotector tries to read the
> stack canary from the PDA ... crashing the bootup.
> 
> the solution was suggested by Arjan van de Ven: to exclude paravirt.c
> from stackprotector, too many lowlevel functionality is in it. It's
> not like we'll have paravirt functions with character arrays on
> their stack anyway...
> 
> Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  arch/x86/kernel/Makefile |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-x86.q/arch/x86/kernel/Makefile
> ===================================================================
> --- linux-x86.q.orig/arch/x86/kernel/Makefile
> +++ linux-x86.q/arch/x86/kernel/Makefile
> @@ -15,6 +15,7 @@ nostackp := $(call cc-option, -fno-stack
>  CFLAGS_vsyscall_64.o	:= $(PROFILING) -g0 $(nostackp)
>  CFLAGS_hpet.o		:= $(nostackp)
>  CFLAGS_tsc_64.o		:= $(nostackp)
> +CFLAGS_paravirt.o	:= $(nostackp)
>  
>  obj-y			:= process_$(BITS).o signal_$(BITS).o entry_$(BITS).o
>  obj-y			+= traps_$(BITS).o irq_$(BITS).o
> 

-- 
James Morris
<jmorris@...ei.org>
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