On 7/24/19 1:11 PM, Kirill A. Shutemov wrote:
> On Wed, Jul 24, 2019 at 05:34:26PM +0000, Lendacky, Thomas wrote:
>> On 7/24/19 12:06 PM, Robin Murphy wrote:
>>> On 24/07/2019 17:42, Lendacky, Thomas wrote:
>>>> On 7/24/19 10:55 AM, Kirill A. Shutemov wrote:
>>>>> On Wed, Jul 10, 2019 at 07:01:19PM +0000, Lendacky, Thomas wrote:
>>>>>> @@ -351,6 +355,32 @@ bool sev_active(void)
>>>>>> }
>>>>>> EXPORT_SYMBOL(sev_active);
>>>>>> +/* Override for DMA direct allocation check -
>>>>>> ARCH_HAS_FORCE_DMA_UNENCRYPTED */
>>>>>> +bool force_dma_unencrypted(struct device *dev)
>>>>>> +{
>>>>>> + /*
>>>>>> + * For SEV, all DMA must be to unencrypted addresses.
>>>>>> + */
>>>>>> + if (sev_active())
>>>>>> + return true;
>>>>>> +
>>>>>> + /*
>>>>>> + * For SME, all DMA must be to unencrypted addresses if the
>>>>>> + * device does not support DMA to addresses that include the
>>>>>> + * encryption mask.
>>>>>> + */
>>>>>> + if (sme_active()) {
>>>>>> + u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask));
>>>>>> + u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask,
>>>>>> + dev->bus_dma_mask);
>>>>>> +
>>>>>> + if (dma_dev_mask <= dma_enc_mask)
>>>>>> + return true;
>>>>>
>>>>> Hm. What is wrong with the dev mask being equal to enc mask? IIUC, it
>>>>> means that device mask is wide enough to cover encryption bit, doesn't it?
>>>>
>>>> Not really... it's the way DMA_BIT_MASK works vs bit numbering. Let's say
>>>> that sme_me_mask has bit 47 set. __ffs64 returns 47 and DMA_BIT_MASK(47)
>>>> will generate a mask without bit 47 set (0x7fffffffffff). So the check
>>>> will catch anything that does not support at least 48-bit DMA.
>>>
>>> Couldn't that be expressed as just:
>>>
>>> if (sme_me_mask & dma_dev_mask == sme_me_mask)
>>
>> Actually !=, but yes, it could have been done like that, I just didn't
>> think of it.
>
> I'm looking into generalizing the check to cover MKTME.
>
> Leaving off the Kconfig changes and moving the check to other file,
> doest
> the change below look reasonable to you. It's only build tested so far.
>
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index fece30ca8b0c..6c86adcd02da 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -355,6 +355,8 @@ EXPORT_SYMBOL(sev_active);
> /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED
> */
> bool force_dma_unencrypted(struct device *dev)
> {
> + u64 dma_enc_mask;
> +
> /*
> * For SEV, all DMA must be to unencrypted addresses.
> */
> @@ -362,18 +364,20 @@ bool force_dma_unencrypted(struct device *dev)
> return true;
>
> /*
> - * For SME, all DMA must be to unencrypted addresses if the
> - * device does not support DMA to addresses that include the
> - * encryption mask.
> + * For SME and MKTME, all DMA must be to unencrypted addresses if the
> + * device does not support DMA to addresses that include the encryption
> + * mask.
> */
> - if (sme_active()) {
> - u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask));
> - u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask,
> - dev->bus_dma_mask);
> + if (!sme_active() && !mktme_enabled())
> + return false;
>
> - if (dma_dev_mask <= dma_enc_mask)
> - return true;
> - }
> + dma_enc_mask = sme_me_mask | mktme_keyid_mask();
> +
> + if (dev->coherent_dma_mask && (dev->coherent_dma_mask & dma_enc_mask)
> != dma_enc_mask)
> + return true;
> +
> + if (dev->bus_dma_mask && (dev->bus_dma_mask & dma_enc_mask) !=
> dma_enc_mask)
> + return true;
Do you want to err on the side of caution and return true if both masks
are zero? You could do the min_not_zero step and then return true if the
result is zero. Then just make the one comparison against dma_enc_mask.
Thanks,
Tom
>
> return false;
> }
>
