[PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Brijesh Singh]

SEV guest fails to update the UEFI runtime variables stored in the
flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
when SEV is active") unconditionally maps all the UEFI runtime data
as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
guest and hypervisor can access the data.

Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: linux-efi@vger.kernel.org
Cc: kvm@vger.kernel.org
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: <stable@vger.kernel.org> # 4.15.x
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/platform/efi/efi_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 77873ce..5f2eb32 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
 	if (!(md->attribute & EFI_MEMORY_WB))
 		flags |= _PAGE_PCD;
 
-	if (sev_active())
+	if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
 		flags |= _PAGE_ENC;
 
 	pfn = md->phys_addr >> PAGE_SHIFT;
-- 
2.7.4

Re: [PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Ard Biesheuvel]

On 3 July 2018 at 15:32, Brijesh Singh <brijesh.singh@amd.com> wrote:
> SEV guest fails to update the UEFI runtime variables stored in the
> flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
> when SEV is active") unconditionally maps all the UEFI runtime data
> as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
> as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
> guest and hypervisor can access the data.
>

I'm uncomfortable having to carry these heuristics in the kernel. The
UEFI memory map should be the definitive source of information
regarding how the OS should map the regions it describes, and if we
need to guess the encryption status, we are likely to get it wrong at
least some of the times.

Is any work underway to get the UEFI spec extended to take encrypted
memory into account? I am aware that we cannot disclose specifics, but
you should be able to disclose whether it is under discussion or not.

In the mean time, we will have to do something, I know that, but I
would like to discuss the proper solution before proceeding with the
stop gap one.

-- 
Ard.


> Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: linux-efi@vger.kernel.org
> Cc: kvm@vger.kernel.org
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: <stable@vger.kernel.org> # 4.15.x
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  arch/x86/platform/efi/efi_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 77873ce..5f2eb32 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
>         if (!(md->attribute & EFI_MEMORY_WB))
>                 flags |= _PAGE_PCD;
>
> -       if (sev_active())
> +       if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
>                 flags |= _PAGE_ENC;
>
>         pfn = md->phys_addr >> PAGE_SHIFT;
> --
> 2.7.4
>

Re: [PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Tom Lendacky]

On 7/3/2018 8:32 AM, Brijesh Singh wrote:
> SEV guest fails to update the UEFI runtime variables stored in the
> flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
> when SEV is active") unconditionally maps all the UEFI runtime data
> as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
> as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
> guest and hypervisor can access the data.
> 
> Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: linux-efi@vger.kernel.org
> Cc: kvm@vger.kernel.org
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: <stable@vger.kernel.org> # 4.15.x
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>  arch/x86/platform/efi/efi_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 77873ce..5f2eb32 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
>  	if (!(md->attribute & EFI_MEMORY_WB))
>  		flags |= _PAGE_PCD;
>  
> -	if (sev_active())
> +	if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
>  		flags |= _PAGE_ENC;
>  
>  	pfn = md->phys_addr >> PAGE_SHIFT;
> 

Re: [PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Ard Biesheuvel]

On 3 July 2018 at 15:32, Brijesh Singh <brijesh.singh@amd.com> wrote:
> SEV guest fails to update the UEFI runtime variables stored in the
> flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
> when SEV is active") unconditionally maps all the UEFI runtime data
> as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
> as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
> guest and hypervisor can access the data.
>
> Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: linux-efi@vger.kernel.org
> Cc: kvm@vger.kernel.org
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: <stable@vger.kernel.org> # 4.15.x
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  arch/x86/platform/efi/efi_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 77873ce..5f2eb32 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
>         if (!(md->attribute & EFI_MEMORY_WB))
>                 flags |= _PAGE_PCD;
>
> -       if (sev_active())
> +       if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
>                 flags |= _PAGE_ENC;
>
>         pfn = md->phys_addr >> PAGE_SHIFT;

Is it safe to only update this occurrence and not the one in
efi_runtime_update_mappings() ?

Re: [PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Brijesh Singh]

Hi Ard,


On 07/11/2018 05:00 AM, Ard Biesheuvel wrote:
> On 3 July 2018 at 15:32, Brijesh Singh <brijesh.singh@amd.com> wrote:
>> SEV guest fails to update the UEFI runtime variables stored in the
>> flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
>> when SEV is active") unconditionally maps all the UEFI runtime data
>> as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
>> as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
>> guest and hypervisor can access the data.
>>
>> Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Borislav Petkov <bp@suse.de>
>> Cc: linux-efi@vger.kernel.org
>> Cc: kvm@vger.kernel.org
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Cc: Matt Fleming <matt@codeblueprint.co.uk>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: <stable@vger.kernel.org> # 4.15.x
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>>   arch/x86/platform/efi/efi_64.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
>> index 77873ce..5f2eb32 100644
>> --- a/arch/x86/platform/efi/efi_64.c
>> +++ b/arch/x86/platform/efi/efi_64.c
>> @@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
>>          if (!(md->attribute & EFI_MEMORY_WB))
>>                  flags |= _PAGE_PCD;
>>
>> -       if (sev_active())
>> +       if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
>>                  flags |= _PAGE_ENC;
>>
>>          pfn = md->phys_addr >> PAGE_SHIFT;
> 
> Is it safe to only update this occurrence and not the one in
> efi_runtime_update_mappings() ?
> 


It's safe to update this occurrence only. The SEV support is added
in recent EDK2 bios, and the version of bios provides the
EFI_MEMORY_ATTRIBUTE_TABLE. Hence the efi_enabled(EFI_MEM_ATTR) check in 
efi_runtime_update_mappings() will always be true. When EFI_MEM_ATTR is
set the code updates the mapping and returns (see below)

void __init efi_runtime_update_mappings(void)
{
    .....
    .....

    /*
     * Use the EFI Memory Attribute Table for mapping permissions if it
     * exists, since it is intended to supersede EFI_PROPERTIES_TABLE.
     */
     if (efi_enabled(EFI_MEM_ATTR)) {
	efi_memattr_apply_permissions(NULL, efi_update_mem_attr);
	return;
     }


    ...

}

The EFI_MEMORY_ATTRIBUTE_TABLE table does not include MMIO regions, the
table describes the memory protections to EFI runtime code and data
regions only. Both EFI runtime code and data should be mapped as
encrypted. Hence I skipped updating the efi_runtime_update_mappings().


thanks

Re: [PATCH] x86/efi: Access EFI MMIO data as unencrypted when SEV is active

[Ard Biesheuvel]

On 17 July 2018 at 03:15, Brijesh Singh <brijesh.singh@amd.com> wrote:
> Hi Ard,
>
>
>
> On 07/11/2018 05:00 AM, Ard Biesheuvel wrote:
>>
>> On 3 July 2018 at 15:32, Brijesh Singh <brijesh.singh@amd.com> wrote:
>>>
>>> SEV guest fails to update the UEFI runtime variables stored in the
>>> flash. commit 1379edd59673 ("x86/efi: Access EFI data as encrypted
>>> when SEV is active") unconditionally maps all the UEFI runtime data
>>> as 'encrypted' (C=1). When SEV is active the UEFI runtime data marked
>>> as EFI_MEMORY_MAPPED_IO should be mapped as 'unencrypted' so that both
>>> guest and hypervisor can access the data.
>>>
>>> Fixes: 1379edd59673 (x86/efi: Access EFI data as encrypted ...)
>>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Borislav Petkov <bp@suse.de>
>>> Cc: linux-efi@vger.kernel.org
>>> Cc: kvm@vger.kernel.org
>>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>> Cc: Matt Fleming <matt@codeblueprint.co.uk>
>>> Cc: Andy Lutomirski <luto@kernel.org>
>>> Cc: <stable@vger.kernel.org> # 4.15.x
>>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>>> ---
>>>   arch/x86/platform/efi/efi_64.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/platform/efi/efi_64.c
>>> b/arch/x86/platform/efi/efi_64.c
>>> index 77873ce..5f2eb32 100644
>>> --- a/arch/x86/platform/efi/efi_64.c
>>> +++ b/arch/x86/platform/efi/efi_64.c
>>> @@ -417,7 +417,7 @@ static void __init __map_region(efi_memory_desc_t
>>> *md, u64 va)
>>>          if (!(md->attribute & EFI_MEMORY_WB))
>>>                  flags |= _PAGE_PCD;
>>>
>>> -       if (sev_active())
>>> +       if (sev_active() && md->type != EFI_MEMORY_MAPPED_IO)
>>>                  flags |= _PAGE_ENC;
>>>
>>>          pfn = md->phys_addr >> PAGE_SHIFT;
>>
>>
>> Is it safe to only update this occurrence and not the one in
>> efi_runtime_update_mappings() ?
>>
>
>
> It's safe to update this occurrence only. The SEV support is added
> in recent EDK2 bios, and the version of bios provides the
> EFI_MEMORY_ATTRIBUTE_TABLE. Hence the efi_enabled(EFI_MEM_ATTR) check in
> efi_runtime_update_mappings() will always be true. When EFI_MEM_ATTR is
> set the code updates the mapping and returns (see below)
>
> void __init efi_runtime_update_mappings(void)
> {
>    .....
>    .....
>
>    /*
>     * Use the EFI Memory Attribute Table for mapping permissions if it
>     * exists, since it is intended to supersede EFI_PROPERTIES_TABLE.
>     */
>     if (efi_enabled(EFI_MEM_ATTR)) {
>         efi_memattr_apply_permissions(NULL, efi_update_mem_attr);
>         return;
>     }
>
>
>    ...
>
> }
>
> The EFI_MEMORY_ATTRIBUTE_TABLE table does not include MMIO regions, the
> table describes the memory protections to EFI runtime code and data
> regions only. Both EFI runtime code and data should be mapped as
> encrypted. Hence I skipped updating the efi_runtime_update_mappings().
>

Ok, thanks for clearing that up

Queued in efi/urgent