Re: [PATCH] x86/reboot: Don't corrupt memory on non-BIOS systems

[Ingo Molnar <mingo@kernel.org>]

* Roman Kisel <romank@linux.microsoft.com> wrote:

> native_machine_emergency_restart() writes unconditionally
> to the physical address of 0x472 to pass the warm reboot
> flags to BIOS. The BIOS reads this on booting to bypass memory
> test and do the warm boot. On the non-BIOS systems, other
> means have to be employed, and this write is a memory corruption.
> 
> Fix that by moving the offending write into the case where
> the machine is rebooted via BIOS.
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  arch/x86/kernel/reboot.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 615922838c51..6eec8653493f 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -637,9 +637,8 @@ static void native_machine_emergency_restart(void)
>  
>  	tboot_shutdown(TB_SHUTDOWN_REBOOT);
>  
> -	/* Tell the BIOS if we want cold or warm reboot */
> +	/* Tell the firmware if we want cold or warm reboot */
>  	mode = reboot_mode == REBOOT_WARM ? 0x1234 : 0;
> -	*((unsigned short *)__va(0x472)) = mode;
>  
>  	/*
>  	 * If an EFI capsule has been registered with the firmware then
> @@ -681,6 +680,7 @@ static void native_machine_emergency_restart(void)
>  			break;
>  
>  		case BOOT_BIOS:
> +			*((unsigned short *)__va(0x472)) = mode;
>  			machine_real_restart(MRR_BIOS);

If the value of 0x472 is only meaningful in the legacy 'BOOT_BIOS' 
case, then at minimum the whole block should be moved to that case, not 
just the setting.

Thanks,

	Ingo