Re: [patch 04/09] x86_64: avoid SMP boot up race

[Horms <horms@verge.net.au>]

Hi,

I'm wondering if anyone could comment on if this could
be conceived as a security bug. My initial instinct was
yes, but on further considertation I can't conceive
a way it could be exploited, well not by anyone
who couldn't DoS the box in any number of other ways,
including shutting it down.

On Wed, Jun 08, 2005 at 05:04:08PM -0700, Chris Wright wrote:
> Keep interrupts disabled during smp bootup
> 
> This avoids a race that breaks SMP bootup on some machines.
> The race is not fully plugged (that is only done with much
> more changes in 2.6.12), but should be good enough
> for most people.
> 
> Keeping the interrupts disabled here is ok because we
> don't rely on the timer interrupt for local APIC
> timer setup, but always read the timer registers
> directly.
> 
> (originally from Rusty Russell iirc) 
> 
> Signed-off-by: ak@suse.de
> Signed-off-by: Chris Wright <chrisw@osdl.org>
> 
> diff -u linux/arch/x86_64/kernel/apic.c-o linux/arch/x86_64/kernel/apic.c
> --- linux/arch/x86_64/kernel/apic.c-o	2005-05-31 16:40:01.000000000 +0200
> +++ linux/arch/x86_64/kernel/apic.c	2005-05-31 16:44:05.000000000 +0200
> @@ -775,9 +775,7 @@
>  
>  void __init setup_secondary_APIC_clock(void)
>  {
> -	local_irq_disable(); /* FIXME: Do we need this? --RR */
>  	setup_APIC_timer(calibration_result);
> -	local_irq_enable();
>  }
>  
>  void __init disable_APIC_timer(void)
> diff -u linux/arch/x86_64/kernel/smpboot.c-o linux-2.6.11/arch/x86_64/kernel/smpboot.c
> --- linux/arch/x86_64/kernel/smpboot.c-o	2005-03-21 14:04:11.000000000 +0100
> +++ linux/arch/x86_64/kernel/smpboot.c	2005-05-31 16:44:07.000000000 +0200
> @@ -309,8 +309,6 @@
>  	Dprintk("CALLIN, before setup_local_APIC().\n");
>  	setup_local_APIC();
>  
> -	local_irq_enable();
> -
>  	/*
>  	 * Get our bogomips.
>  	 */
> @@ -324,8 +322,6 @@
>  	 */
>   	smp_store_cpu_info(cpuid);
>  
> -	local_irq_disable();
> -
>  	/*
>  	 * Allow the master to continue.
>  	 */
> 
> -
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-- 
Horms