Re: [PATCH v5 19/32] x86/mm: Add support to access persistent memory in the clear

[Borislav Petkov]

On Tue, Apr 18, 2017 at 04:19:42PM -0500, Tom Lendacky wrote:
> Persistent memory is expected to persist across reboots. The encryption
> key used by SME will change across reboots which will result in corrupted
> persistent memory.  Persistent memory is handed out by block devices
> through memory remapping functions, so be sure not to map this memory as
> encrypted.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/mm/ioremap.c |   31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index bce0604..55317ba 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -425,17 +425,46 @@ void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
>   * Examine the physical address to determine if it is an area of memory
>   * that should be mapped decrypted.  If the memory is not part of the
>   * kernel usable area it was accessed and created decrypted, so these
> - * areas should be mapped decrypted.
> + * areas should be mapped decrypted. And since the encryption key can
> + * change across reboots, persistent memory should also be mapped
> + * decrypted.
>   */
>  static bool memremap_should_map_decrypted(resource_size_t phys_addr,
>  					  unsigned long size)
>  {
> +	int is_pmem;
> +
> +	/*
> +	 * Check if the address is part of a persistent memory region.
> +	 * This check covers areas added by E820, EFI and ACPI.
> +	 */
> +	is_pmem = region_intersects(phys_addr, size, IORESOURCE_MEM,
> +				    IORES_DESC_PERSISTENT_MEMORY);
> +	if (is_pmem != REGION_DISJOINT)
> +		return true;
> +
> +	/*
> +	 * Check if the non-volatile attribute is set for an EFI
> +	 * reserved area.
> +	 */
> +	if (efi_enabled(EFI_BOOT)) {
> +		switch (efi_mem_type(phys_addr)) {
> +		case EFI_RESERVED_TYPE:
> +			if (efi_mem_attributes(phys_addr) & EFI_MEMORY_NV)
> +				return true;
> +			break;
> +		default:
> +			break;
> +		}
> +	}
> +
>  	/* Check if the address is outside kernel usable area */
>  	switch (e820__get_entry_type(phys_addr, phys_addr + size - 1)) {
>  	case E820_TYPE_RESERVED:
>  	case E820_TYPE_ACPI:
>  	case E820_TYPE_NVS:
>  	case E820_TYPE_UNUSABLE:
> +	case E820_TYPE_PRAM:

Can't you simply add:

	case E820_TYPE_PMEM:

here too and thus get rid of the region_intersects() thing above?

Because, for example, e820_type_to_iores_desc() maps E820_TYPE_PMEM to
IORES_DESC_PERSISTENT_MEMORY so those should be equivalent...

-- 
Regards/Gruss,
    Boris.

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