[PATCH v3 0/2] Fix SEV user-space mapping of unencrypted coherent memory

[PATCH v3 0/2] Fix SEV user-space mapping of unencrypted coherent memory

[Thomas Hellström (VMware)]

This patchset fixes dma_mmap_coherent() mapping of unencrypted memory in
otherwise encrypted environments, where it would incorrectly map that memory as
encrypted.

With SEV and sometimes with SME encryption, The dma api coherent memory is
typically unencrypted, meaning the linear kernel map has the encryption
bit cleared. However, default page protection returned from vm_get_page_prot()
has the encryption bit set. So to compute the correct page protection we need
to clear the encryption bit.

Also, in order for the encryption bit setting to survive across do_mmap() and
mprotect_fixup(), We need to make pgprot_modify() aware of it and not touch it.
Therefore make sme_me_mask part of _PAGE_CHG_MASK and make sure
pgprot_modify() preserves also cleared bits that are part of _PAGE_CHG_MASK,
not just set bits. The use of pgprot_modify() is currently quite limited and
easy to audit.

(Note that the encryption status is not logically encoded in the pfn but in
the page protection even if an address line in the physical address is used).

The patchset has seen some sanity testing by exporting dma_pgprot() and
using it in the vmwgfx mmap handler with SEV enabled.

As far as I can tell there are no current users of dma_mmap_coherent() with
SEV or SME encryption which means that there is no need to CC stable.

Changes since:
RFC:
- Make sme_me_mask port of _PAGE_CHG_MASK rather than using it by its own in
  pgprot_modify().
v2:
- Clarify which use-cases this patchset actually fixes.
v3:
- Use _PAGE_ENC instead of sme_me_mask in the definition of _PAGE_CHG_MASK

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>

[PATCH v3 1/2] x86: Don't let pgprot_modify() change the page encryption bit

[Thomas Hellström (VMware)]

From: Thomas Hellstrom <thellstrom@vmware.com>

When SEV or SME is enabled and active, vm_get_page_prot() typically
returns with the encryption bit set. This means that users of
pgprot_modify(, vm_get_page_prot()) (mprotect_fixup, do_mmap) end up with
a value of vma->vm_pg_prot that is not consistent with the intended
protection of the PTEs. This is also important for fault handlers that
rely on the VMA vm_page_prot to set the page protection. Fix this by
not allowing pgprot_modify() to change the encryption bit, similar to
how it's done for PAT bits.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
---
 arch/x86/include/asm/pgtable.h       | 7 +++++--
 arch/x86/include/asm/pgtable_types.h | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 0bc530c4eb13..1e6bb4c25334 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -624,12 +624,15 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 	return __pmd(val);
 }
 
-/* mprotect needs to preserve PAT bits when updating vm_page_prot */
+/*
+ * mprotect needs to preserve PAT and encryption bits when updating
+ * vm_page_prot
+ */
 #define pgprot_modify pgprot_modify
 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 {
 	pgprotval_t preservebits = pgprot_val(oldprot) & _PAGE_CHG_MASK;
-	pgprotval_t addbits = pgprot_val(newprot);
+	pgprotval_t addbits = pgprot_val(newprot) & ~_PAGE_CHG_MASK;
 	return __pgprot(preservebits | addbits);
 }
 
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index b5e49e6bac63..8267dd426b15 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -123,7 +123,7 @@
  */
 #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
 			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
-			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
+			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_ENC)
 #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
 
 /*
-- 
2.20.1

[PATCH v3 2/2] dma-mapping: Fix dma_pgprot() for unencrypted coherent pages

[Thomas Hellström (VMware)]

From: Thomas Hellstrom <thellstrom@vmware.com>

When dma_mmap_coherent() sets up a mapping to unencrypted coherent memory
under SEV encryption and sometimes under SME encryption, it will actually
set up an encrypted mapping rather than an unencrypted, causing devices
that DMAs from that memory to read encrypted contents. Fix this.

When force_dma_unencrypted() returns true, the linear kernel map of the
coherent pages have had the encryption bit explicitly cleared and the
page content is unencrypted. Make sure that any additional PTEs we set
up to these pages also have the encryption bit cleared by having
dma_pgprot() return a protection with the encryption bit cleared in this
case.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
---
 kernel/dma/mapping.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index b0038ca3aa92..2b499dcae74f 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -157,6 +157,8 @@ EXPORT_SYMBOL(dma_get_sgtable_attrs);
  */
 pgprot_t dma_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs)
 {
+	if (force_dma_unencrypted(dev))
+		prot = pgprot_decrypted(prot);
 	if (dev_is_dma_coherent(dev) ||
 	    (IS_ENABLED(CONFIG_DMA_NONCOHERENT_CACHE_SYNC) &&
              (attrs & DMA_ATTR_NON_CONSISTENT)))
-- 
2.20.1

Re: [PATCH v3 0/2] Fix SEV user-space mapping of unencrypted coherent memory

[Christoph Hellwig]

This looks sensibe to me.  x86 folks let me know if you guys want
to pick this up or if I should take it.

On Tue, Sep 17, 2019 at 03:01:13PM +0200, Thomas Hellström (VMware) wrote:
> As far as I can tell there are no current users of dma_mmap_coherent() with
> SEV or SME encryption which means that there is no need to CC stable.

Note that the usbfs access really should use it, as the current version
is completely broken on non-coherent architectures.  That already
triggered on x86 dma_mmap_coherent fix.  So I'd actually like to see
a stable backport to avoid hitting surprises.

Re: [PATCH v3 1/2] x86: Don't let pgprot_modify() change the page encryption bit

[Dave Hansen]

On 9/17/19 6:01 AM, Thomas Hellström (VMware) wrote:
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index b5e49e6bac63..8267dd426b15 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -123,7 +123,7 @@
>   */
>  #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
>  			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
> -			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
> +			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_ENC)
>  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)

My only nit with what remains is that it expands the infestation of
things that look like a simple macro but are not.

I'm debating whether we want to go fix that now, though.

Re: [PATCH v3 1/2] x86: Don't let pgprot_modify() change the page encryption bit

[Thomas Hellstrom]

Hi,

On 9/18/19 7:57 PM, Dave Hansen wrote:
> On 9/17/19 6:01 AM, Thomas Hellström (VMware) wrote:
>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
>> index b5e49e6bac63..8267dd426b15 100644
>> --- a/arch/x86/include/asm/pgtable_types.h
>> +++ b/arch/x86/include/asm/pgtable_types.h
>> @@ -123,7 +123,7 @@
>>   */
>>  #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
>>  			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
>> -			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
>> +			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_ENC)
>>  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
> My only nit with what remains is that it expands the infestation of
> things that look like a simple macro but are not.
>
> I'm debating whether we want to go fix that now, though.
>
Any chance for an ack on this? It's really a small change that, as we've
found out, fixes an existing problem.

Thanks,

Thomas

Re: [PATCH v3 1/2] x86: Don't let pgprot_modify() change the page encryption bit

[Dave Hansen]

On 9/30/19 10:54 PM, Thomas Hellstrom wrote:
> Hi,
> 
> On 9/18/19 7:57 PM, Dave Hansen wrote:
>> On 9/17/19 6:01 AM, Thomas Hellström (VMware) wrote:
>>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
>>> index b5e49e6bac63..8267dd426b15 100644
>>> --- a/arch/x86/include/asm/pgtable_types.h
>>> +++ b/arch/x86/include/asm/pgtable_types.h
>>> @@ -123,7 +123,7 @@
>>>   */
>>>  #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
>>>  			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
>>> -			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
>>> +			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | _PAGE_ENC)
>>>  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
>> My only nit with what remains is that it expands the infestation of
>> things that look like a simple macro but are not.
>>
>> I'm debating whether we want to go fix that now, though.
>>
> Any chance for an ack on this? It's really a small change that, as we've
> found out, fixes an existing problem.

Yes, feel free to add:

Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>