linux-kernel - Re: [RFC PATCH v2 13/20] x86: Decrypt trampoline area if memory encryption is active

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Date:   Mon, 12 Sep 2016 10:43:32 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 13/20] x86: Decrypt trampoline area if memory
 encryption is active

On 09/09/2016 12:34 PM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:37:57PM -0500, 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
> 
> s/cpu/CPU/... always :-)

Ok.

> 
>> 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@....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..f74925f 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 non-encrypted memory in order to bring up other processors
> 
> Let's stick with either "unencrypted" - I'd prefer that one - or
> "non-encrypted" nomenclature so that there's no distraction. I see both
> versions in the patchset.

Yup, I'll audit the code and make everything consistent.

Thanks,
Tom

>