diff mbox series

[02/10] x86/mm/cpa: Reject incorrect encryption change requests

Message ID 20231017202505.340906-3-rick.p.edgecombe@intel.com
State New
Headers
Series Handle set_memory_XXcrypted() errors |

Commit Message

Edgecombe, Rick P Oct. 17, 2023, 8:24 p.m. UTC 
  Kernel memory is "encrypted" by default.  Some callers may "decrypt" it
in order to share it with things outside the kernel like a device or an
untrusted VMM.

There is nothing to stop set_memory_encrypted() from being passed memory
that is already "encrypted" (aka. "private" on TDX).  In fact, some
callers do this because ... $REASONS.  Unfortunately, part of the TDX
decrypted=>encrypted transition is truly one way*.  It can't handle
being asked to encrypt an already encrypted page

Allow __set_memory_enc_pgtable() to detect already-encrypted memory
before it hits the TDX code.

* The one way part is "page acceptance"

[commit log written by Dave Hansen]
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/mm/pat/set_memory.c | 41 +++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

Comments

Ingo Molnar Oct. 18, 2023, 8:44 a.m. UTC | #1 
* Rick Edgecombe <rick.p.edgecombe@intel.com> wrote:

> Kernel memory is "encrypted" by default.  Some callers may "decrypt" it
> in order to share it with things outside the kernel like a device or an
> untrusted VMM.
> 
> There is nothing to stop set_memory_encrypted() from being passed memory
> that is already "encrypted" (aka. "private" on TDX).  In fact, some
> callers do this because ... $REASONS.  Unfortunately, part of the TDX
> decrypted=>encrypted transition is truly one way*.  It can't handle
> being asked to encrypt an already encrypted page
> 
> Allow __set_memory_enc_pgtable() to detect already-encrypted memory
> before it hits the TDX code.
> 
> * The one way part is "page acceptance"
> 
> [commit log written by Dave Hansen]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---
>  arch/x86/mm/pat/set_memory.c | 41 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index bda9f129835e..1238b0db3e33 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -2122,6 +2122,21 @@ int set_memory_global(unsigned long addr, int numpages)
>  				    __pgprot(_PAGE_GLOBAL), 0);
>  }
>  
> +static bool kernel_vaddr_encryped(unsigned long addr, bool enc)
> +{
> +	unsigned int level;
> +	pte_t *pte;
> +
> +	pte = lookup_address(addr, &level);
> +	if (!pte)
> +		return false;
> +
> +	if (enc)
> +		return pte_val(*pte) == cc_mkenc(pte_val(*pte));
> +
> +	return pte_val(*pte) == cc_mkdec(pte_val(*pte));
> +}
> +
>  /*
>   * __set_memory_enc_pgtable() is used for the hypervisors that get
>   * informed about "encryption" status via page tables.
> @@ -2130,7 +2145,7 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  {
>  	pgprot_t empty = __pgprot(0);
>  	struct cpa_data cpa;
> -	int ret;
> +	int ret, numpages_in_state = 0;
>  
>  	/* Should not be working on unaligned addresses */
>  	if (WARN_ONCE(addr & ~PAGE_MASK, "misaligned address: %#lx\n", addr))
> @@ -2143,6 +2158,30 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  	cpa.mask_clr = enc ? pgprot_decrypted(empty) : pgprot_encrypted(empty);
>  	cpa.pgd = init_mm.pgd;
>  
> +	/*
> +	 * If any page is already in the right state, bail with an error
> +	 * because the code doesn't handled it. This is likely because

Grammar mistake here.

> +	 * something has gone wrong and isn't worth optimizing for.
> +	 *
> +	 * If all the memory pages are already in the desired state return
> +	 * success.

Missing comma.

> +	 *
> +	 * kernel_vaddr_encryped() does not synchronize against huge page
> +	 * splits so take pgd_lock. A caller doing strange things could

Missing comma.

Thanks,

	Ingo
Edgecombe, Rick P Oct. 18, 2023, 3:53 p.m. UTC | #2 
On Wed, 2023-10-18 at 10:44 +0200, Ingo Molnar wrote:
> > +       /*
> > +        * If any page is already in the right state, bail with an
> > error
> > +        * because the code doesn't handled it. This is likely
> > because
> 
> Grammar mistake here.
> 
> > +        * something has gone wrong and isn't worth optimizing for.
> > +        *
> > +        * If all the memory pages are already in the desired state
> > return
> > +        * success.
> 
> Missing comma.
> 
> > +        *
> > +        * kernel_vaddr_encryped() does not synchronize against
> > huge page
> > +        * splits so take pgd_lock. A caller doing strange things
> > could
> 
> Missing comma.

Oh, yep. Thanks.
diff mbox series

Patch

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bda9f129835e..1238b0db3e33 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2122,6 +2122,21 @@  int set_memory_global(unsigned long addr, int numpages)
 				    __pgprot(_PAGE_GLOBAL), 0);
 }
 
+static bool kernel_vaddr_encryped(unsigned long addr, bool enc)
+{
+	unsigned int level;
+	pte_t *pte;
+
+	pte = lookup_address(addr, &level);
+	if (!pte)
+		return false;
+
+	if (enc)
+		return pte_val(*pte) == cc_mkenc(pte_val(*pte));
+
+	return pte_val(*pte) == cc_mkdec(pte_val(*pte));
+}
+
 /*
  * __set_memory_enc_pgtable() is used for the hypervisors that get
  * informed about "encryption" status via page tables.
@@ -2130,7 +2145,7 @@  static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 {
 	pgprot_t empty = __pgprot(0);
 	struct cpa_data cpa;
-	int ret;
+	int ret, numpages_in_state = 0;
 
 	/* Should not be working on unaligned addresses */
 	if (WARN_ONCE(addr & ~PAGE_MASK, "misaligned address: %#lx\n", addr))
@@ -2143,6 +2158,30 @@  static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 	cpa.mask_clr = enc ? pgprot_decrypted(empty) : pgprot_encrypted(empty);
 	cpa.pgd = init_mm.pgd;
 
+	/*
+	 * If any page is already in the right state, bail with an error
+	 * because the code doesn't handled it. This is likely because
+	 * something has gone wrong and isn't worth optimizing for.
+	 *
+	 * If all the memory pages are already in the desired state return
+	 * success.
+	 *
+	 * kernel_vaddr_encryped() does not synchronize against huge page
+	 * splits so take pgd_lock. A caller doing strange things could
+	 * get a new PMD mid level PTE confused with a huge PMD entry. Just
+	 * lock to tie up loose ends.
+	 */
+	spin_lock(&pgd_lock);
+	for (int i = 0; i < numpages; i++) {
+		if (kernel_vaddr_encryped(addr + (PAGE_SIZE * i), enc))
+			numpages_in_state++;
+	}
+	spin_unlock(&pgd_lock);
+	if (numpages_in_state == numpages)
+		return 0;
+	else if (numpages_in_state)
+		return 1;
+
 	/* Must avoid aliasing mappings in the highmem code */
 	kmap_flush_unused();
 	vm_unmap_aliases();