linux-kernel - Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode

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Date:	Tue, 25 Nov 2014 13:43:26 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Borislav Petkov <bp@...e.de>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Richard Hendershot <rshendershot@...si.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode_ldr
 on 32-bit

On 11/25/2014 01:24 PM, Borislav Petkov wrote:
> On Tue, Nov 25, 2014 at 01:12:10PM -0500, Boris Ostrovsky wrote:
>> On 11/19/2014 03:52 PM, Greg Kroah-Hartman wrote:
>>> 3.17-stable review patch.  If anyone has any objections, please let me know.
>>
>> This breaks PV on Xen.
>>
>> -boris
>>
>>> ------------------
>>>
>>> From: Borislav Petkov <bp@...e.de>
>>>
>>> commit 85be07c32496dc264661308e4d9d4e9ccaff8072 upstream.
>>>
>>> We should be accessing it through a pointer, like on the BSP.
>>>
>>> Tested-by: Richard Hendershot <rshendershot@...si.com>
>>> Fixes: 65cef1311d5d ("x86, microcode: Add a disable chicken bit")
>>> Signed-off-by: Borislav Petkov <bp@...e.de>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>
>>> ---
>>>   arch/x86/kernel/cpu/microcode/core_early.c |    2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> --- a/arch/x86/kernel/cpu/microcode/core_early.c
>>> +++ b/arch/x86/kernel/cpu/microcode/core_early.c
>>> @@ -124,7 +124,7 @@ void __init load_ucode_bsp(void)
>>>   static bool check_loader_disabled_ap(void)
>>>   {
>>>   #ifdef CONFIG_X86_32
>>> -	return __pa_nodebug(dis_ucode_ldr);
>>> +	return *((bool *)__pa_nodebug(&dis_ucode_ldr));
> And practically the same line in check_loader_disabled_bsp() doesn't?


I don't think this routine is called on PV.


-boris



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