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

[Tom Lendacky]

On 5/16/2017 9:04 AM, Borislav Petkov wrote:
> 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...

I'll have to double-check this, but I believe that when persistent
memory is identified through the NFIT table it adds it as a resource
but doesn't add it as an e820 entry so I can't rely on the type being
returned as E820_TYPE_PMEM by e820__get_entry_type().

Thanks,
Tom

>