Re: [RFC PATCH v4 21/28] x86: Check for memory encryption on the APs

Tom Lendacky
2017-02-28T23:28:48Z

On 2/27/2017 12:17 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 09:46:47AM -0600, 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 set the SYS_CFG MSR bit to enable
>> memory encryption on that AP and allow the AP to continue start up.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
>> ---
>> arch/x86/include/asm/realmode.h | 12 ++++++++++++
>> arch/x86/realmode/init.c | 4 ++++
>> arch/x86/realmode/rm/trampoline_64.S | 17 +++++++++++++++++
>> 3 files changed, 33 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
>> index 230e190..4f7ef53 100644
>> --- a/arch/x86/include/asm/realmode.h
>> +++ b/arch/x86/include/asm/realmode.h
>> @@ -1,6 +1,15 @@
>> #ifndef _ARCH_X86_REALMODE_H
>> #define _ARCH_X86_REALMODE_H
>>
>> +/*
>> + * Flag bit definitions for use with the flags field of the trampoline header
>> + * int the CONFIG_X86_64 variant.
>
> s/int/in/

Fixed.

>
>> + */
>> +#define TH_FLAGS_SME_ACTIVE_BIT 0
>> +#define TH_FLAGS_SME_ACTIVE BIT(TH_FLAGS_SME_ACTIVE_BIT)
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> #include <linux/types.h>
>> #include <asm/io.h>
>>
>> @@ -38,6 +47,7 @@ struct trampoline_header {
>> u64 start;
>> u64 efer;
>> u32 cr4;
>> + u32 flags;
>> #endif
>> };
>>
>> @@ -69,4 +79,6 @@ static inline size_t real_mode_size_needed(void)
>> void set_real_mode_mem(phys_addr_t mem, size_t size);
>> void reserve_real_mode(void);
>>
>> +#endif /* __ASSEMBLY__ */
>> +
>> #endif /* _ARCH_X86_REALMODE_H */
>> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
>> index 21d7506..5010089 100644
>> --- a/arch/x86/realmode/init.c
>> +++ b/arch/x86/realmode/init.c
>> @@ -102,6 +102,10 @@ static void __init setup_real_mode(void)
>> trampoline_cr4_features = &trampoline_header->cr4;
>> *trampoline_cr4_features = mmu_cr4_features;
>>
>> + trampoline_header->flags = 0;
>> + if (sme_active())
>> + trampoline_header->flags |= TH_FLAGS_SME_ACTIVE;
>> +
>> trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
>> trampoline_pgd[0] = trampoline_pgd_entry.pgd;
>> trampoline_pgd[511] = init_level4_pgt[511].pgd;
>> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
>> index dac7b20..a88c3d1 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"
>>
>> .text
>> @@ -92,6 +93,21 @@ ENTRY(startup_32)
>> movl %edx, %fs
>> movl %edx, %gs
>>
>> + /* Check for memory encryption support */
>
> Let's add some blurb here about this being a safety net in case BIOS
> f*cks up. Which wouldn't be that far-fetched... :-)

That's a good idea, I'll expand on that. I probably won't be that
direct in my comment though :)

Thanks,
Tom

>
>> + bt $TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags
>> + jnc .Ldone
>> + movl $MSR_K8_SYSCFG, %ecx
>> + rdmsr
>> + bts $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
>> + jc .Ldone
>