Subject: Re: [RFC PATCH v3 12/20] x86: Decrypt trampoline area if memory
 encryption is active
To: Borislav Petkov <bp@alien8.de>
References: <20161110003426.3280.2999.stgit@tlendack-t1.amdoffice.net>
 <20161110003708.3280.29934.stgit@tlendack-t1.amdoffice.net>
 <20161117180913.ha5h4bfgrr5u6ccg@pd.tnic>
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From: Tom Lendacky <thomas.lendacky@amd.com>
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Date: Sat, 19 Nov 2016 12:50:24 -0600
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On 11/17/2016 12:09 PM, Borislav Petkov wrote:
> On Wed, Nov 09, 2016 at 06:37:08PM -0600, Tom Lendacky wrote:
>> When Secure Memory Encryption is enabled, the trampoline area must not
>> be encrypted. A CPU running in real mode will not be able to decrypt
>> memory that has been encrypted because it will not be able to use addresses
>> with the memory encryption mask.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  arch/x86/realmode/init.c |    9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
>> index 5db706f1..44ed32a 100644
>> --- a/arch/x86/realmode/init.c
>> +++ b/arch/x86/realmode/init.c
>> @@ -6,6 +6,7 @@
>>  #include <asm/pgtable.h>
>>  #include <asm/realmode.h>
>>  #include <asm/tlbflush.h>
>> +#include <asm/mem_encrypt.h>
>>  
>>  struct real_mode_header *real_mode_header;
>>  u32 *trampoline_cr4_features;
>> @@ -130,6 +131,14 @@ static void __init set_real_mode_permissions(void)
>>  	unsigned long text_start =
>>  		(unsigned long) __va(real_mode_header->text_start);
>>  
>> +	/*
>> +	 * If memory encryption is active, the trampoline area will need to
>> +	 * be in un-encrypted memory in order to bring up other processors
>> +	 * successfully.
>> +	 */
>> +	sme_early_mem_dec(__pa(base), size);
>> +	sme_set_mem_unenc(base, size);
> 
> We're still unsure about the non-encrypted state: dec vs unenc. Please
> unify those for ease of use, code reading, etc etc.
> 
> 	sme_early_decrypt(__pa(base), size);
> 	sme_mark_decrypted(base, size);
> 
> or similar looks much more readable and understandable to me.

Yeah, I'll go through and change everything so that the implication
or action is expressed better.

Thanks,
Tom

>