Re: [RFC PATCH v4 09/28] x86: Add support for early encryption/decryption of memory

[Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>]

On Thu, Feb 16, 2017 at 09:43:58AM -0600, Tom Lendacky wrote:
> Add support to be able to either encrypt or decrypt data in place during
> the early stages of booting the kernel. This does not change the memory
> encryption attribute - it is used for ensuring that data present in either
> an encrypted or decrypted memory area is in the proper state (for example
> the initrd will have been loaded by the boot loader and will not be
> encrypted, but the memory that it resides in is marked as encrypted).
> 
> The early_memmap support is enhanced to specify encrypted and decrypted
> mappings with and without write-protection. The use of write-protection is
> necessary when encrypting data "in place". The write-protect attribute is
> considered cacheable for loads, but not stores. This implies that the
> hardware will never give the core a dirty line with this memtype.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
> ---
>  arch/x86/include/asm/mem_encrypt.h |   15 +++++++
>  arch/x86/mm/mem_encrypt.c          |   79 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 94 insertions(+)

...

> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index d71df97..ac3565c 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -14,6 +14,9 @@
>  #include <linux/init.h>
>  #include <linux/mm.h>
>  
> +#include <asm/tlbflush.h>
> +#include <asm/fixmap.h>
> +
>  extern pmdval_t early_pmd_flags;
>  
>  /*
> @@ -24,6 +27,82 @@
>  unsigned long sme_me_mask __section(.data) = 0;
>  EXPORT_SYMBOL_GPL(sme_me_mask);
>  
> +/* Buffer used for early in-place encryption by BSP, no locking needed */
> +static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);
> +
> +/*
> + * This routine does not change the underlying encryption setting of the
> + * page(s) that map this memory. It assumes that eventually the memory is
> + * meant to be accessed as either encrypted or decrypted but the contents
> + * are currently not in the desired stated.

				       state.

> + *
> + * This routine follows the steps outlined in the AMD64 Architecture
> + * Programmer's Manual Volume 2, Section 7.10.8 Encrypt-in-Place.
> + */
> +static void __init __sme_early_enc_dec(resource_size_t paddr,
> +				       unsigned long size, bool enc)
> +{
> +	void *src, *dst;
> +	size_t len;
> +
> +	if (!sme_me_mask)
> +		return;
> +
> +	local_flush_tlb();
> +	wbinvd();
> +
> +	/*
> +	 * There are limited number of early mapping slots, so map (at most)
> +	 * one page at time.
> +	 */
> +	while (size) {
> +		len = min_t(size_t, sizeof(sme_early_buffer), size);
> +
> +		/*
> +		 * Create write protected mappings for the current format

			  write-protected

> +		 * of the memory.
> +		 */
> +		src = enc ? early_memremap_decrypted_wp(paddr, len) :
> +			    early_memremap_encrypted_wp(paddr, len);
> +
> +		/*
> +		 * Create mappings for the desired format of the memory.
> +		 */

That comment can go - you already say that in the previous one.

> +		dst = enc ? early_memremap_encrypted(paddr, len) :
> +			    early_memremap_decrypted(paddr, len);

Btw, looking at this again, it seems to me that if you write it this
way:

                if (enc) {
                        src = early_memremap_decrypted_wp(paddr, len);
                        dst = early_memremap_encrypted(paddr, len);
                } else {
                        src = early_memremap_encrypted_wp(paddr, len);
                        dst = early_memremap_decrypted(paddr, len);
                }

it might become even more readable. Anyway, just an idea - your decision
which is better.

> +
> +		/*
> +		 * If a mapping can't be obtained to perform the operation,
> +		 * then eventual access of that area will in the desired

s/will //

> +		 * mode will cause a crash.
> +		 */
> +		BUG_ON(!src || !dst);
> +
> +		/*
> +		 * Use a temporary buffer, of cache-line multiple size, to
> +		 * avoid data corruption as documented in the APM.
> +		 */
> +		memcpy(sme_early_buffer, src, len);
> +		memcpy(dst, sme_early_buffer, len);
> +
> +		early_memunmap(dst, len);
> +		early_memunmap(src, len);
> +
> +		paddr += len;
> +		size -= len;
> +	}
> +}
> +
> +void __init sme_early_encrypt(resource_size_t paddr, unsigned long size)
> +{
> +	__sme_early_enc_dec(paddr, size, true);
> +}
> +
> +void __init sme_early_decrypt(resource_size_t paddr, unsigned long size)
> +{
> +	__sme_early_enc_dec(paddr, size, false);
> +}
> +
>  void __init sme_early_init(void)
>  {
>  	unsigned int i;
> 
> 

-- 
Regards/Gruss,
    Boris.

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