Re: [RFC PATCH v3 12/20] x86: Decrypt trampoline area if memory encryption is active

[Borislav Petkov]

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@xxxxxxx>
> ---
>  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.

-- 
Regards/Gruss,
    Boris.

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