Re: [RFC PATCH v2 16/20] x86: Check for memory encryption on the APs
From: Tom Lendacky
Date: Wed Sep 14 2016 - 09:50:50 EST
On 09/12/2016 07:17 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:38:29PM -0500, Tom Lendacky wrote:
>> Add support to check if memory encryption is active in the kernel and that
>> it has been enabled on the AP. If memory encryption is active in the kernel
>> but has not been enabled on the AP then do not allow the AP to continue
>> start up.
>> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
>> arch/x86/include/asm/msr-index.h | 2 ++
>> arch/x86/include/asm/realmode.h | 12 ++++++++++++
>> arch/x86/realmode/init.c | 4 ++++
>> arch/x86/realmode/rm/trampoline_64.S | 19 +++++++++++++++++++
>> 4 files changed, 37 insertions(+)
>> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
>> index dac7b20..94e29f4 100644
>> --- a/arch/x86/realmode/rm/trampoline_64.S
>> +++ b/arch/x86/realmode/rm/trampoline_64.S
>> @@ -30,6 +30,7 @@
>> #include <asm/msr.h>
>> #include <asm/segment.h>
>> #include <asm/processor-flags.h>
>> +#include <asm/realmode.h>
>> #include "realmode.h"
>> @@ -92,6 +93,23 @@ ENTRY(startup_32)
>> movl %edx, %fs
>> movl %edx, %gs
>> + /* Check for memory encryption support */
>> + bt $TH_FLAGS_SME_ENABLE_BIT, pa_tr_flags
>> + jnc .Ldone
>> + movl $MSR_K8_SYSCFG, %ecx
>> + rdmsr
>> + bt $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
>> + jc .Ldone
>> + /*
>> + * Memory encryption is enabled but the MSR has not been set on this
>> + * CPU so we can't continue
> Hmm, let me try to parse this correctly: BSP has SME enabled but the
> BIOS might not've set this on the AP? Really? Is that even possible?
Anything is possible, although it's highly unlikely.
> Because if SME is enabled, that means that MSR_K8_SYSCFG on the BSP
> is set, right?
> Also, I want to rule out here simple BIOS idiocy: if the only problem
> with the bit not being set in the AP is because some BIOS monkey forgot
> to do so, then we should try to set it ourselves and not die for no real
Yes, we can do that. I was debating on which way to go with this. Most
likely this would never happen, but if it did... I can change this to
set the MSR bit and continue.
> Or is there another issue?