diff mbox series

[4.19,2/2] KVM: do not allow mapping valid but non-reference-counted pages

Message ID 20210723201134.3031383-2-ovidiu.panait@windriver.com
State Superseded
Headers show
Series None | expand

Commit Message

Ovidiu Panait July 23, 2021, 8:11 p.m. UTC
From: Nicholas Piggin <npiggin@gmail.com>

commit f8be156be163a052a067306417cd0ff679068c97 upstream.

It's possible to create a region which maps valid but non-refcounted
pages (e.g., tail pages of non-compound higher order allocations). These
host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family
of APIs, which take a reference to the page, which takes it from 0 to 1.
When the reference is dropped, this will free the page incorrectly.

Fix this by only taking a reference on valid pages if it was non-zero,
which indicates it is participating in normal refcounting (and can be
released with put_page).

This addresses CVE-2021-22543.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
---
 virt/kvm/kvm_main.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

Comments

Paolo Bonzini July 26, 2021, 8:16 a.m. UTC | #1
On 23/07/21 22:11, Ovidiu Panait wrote:
> From: Nicholas Piggin <npiggin@gmail.com>

> 

> commit f8be156be163a052a067306417cd0ff679068c97 upstream.

> 

> It's possible to create a region which maps valid but non-refcounted

> pages (e.g., tail pages of non-compound higher order allocations). These

> host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family

> of APIs, which take a reference to the page, which takes it from 0 to 1.

> When the reference is dropped, this will free the page incorrectly.

> 

> Fix this by only taking a reference on valid pages if it was non-zero,

> which indicates it is participating in normal refcounting (and can be

> released with put_page).

> 

> This addresses CVE-2021-22543.

> 

> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

> Tested-by: Paolo Bonzini <pbonzini@redhat.com>

> Cc: stable@vger.kernel.org

> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

> Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>

> ---

>   virt/kvm/kvm_main.c | 19 +++++++++++++++++--

>   1 file changed, 17 insertions(+), 2 deletions(-)

> 

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c

> index 6aeac96bf147..3559eba5f502 100644

> --- a/virt/kvm/kvm_main.c

> +++ b/virt/kvm/kvm_main.c

> @@ -1489,6 +1489,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)

>   	return true;

>   }

>   

> +static int kvm_try_get_pfn(kvm_pfn_t pfn)

> +{

> +	if (kvm_is_reserved_pfn(pfn))

> +		return 1;

> +	return get_page_unless_zero(pfn_to_page(pfn));

> +}

> +

>   static int hva_to_pfn_remapped(struct vm_area_struct *vma,

>   			       unsigned long addr, bool *async,

>   			       bool write_fault, bool *writable,

> @@ -1538,13 +1545,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,

>   	 * Whoever called remap_pfn_range is also going to call e.g.

>   	 * unmap_mapping_range before the underlying pages are freed,

>   	 * causing a call to our MMU notifier.

> +	 *

> +	 * Certain IO or PFNMAP mappings can be backed with valid

> +	 * struct pages, but be allocated without refcounting e.g.,

> +	 * tail pages of non-compound higher order allocations, which

> +	 * would then underflow the refcount when the caller does the

> +	 * required put_page. Don't allow those pages here.

>   	 */

> -	kvm_get_pfn(pfn);

> +	if (!kvm_try_get_pfn(pfn))

> +		r = -EFAULT;

>   

>   out:

>   	pte_unmap_unlock(ptep, ptl);

>   	*p_pfn = pfn;

> -	return 0;

> +

> +	return r;

>   }

>   

>   /*

> 


Acked-by: Paolo Bonzini <pbonzini@redhat.com>
diff mbox series

Patch

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6aeac96bf147..3559eba5f502 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1489,6 +1489,13 @@  static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
 	return true;
 }
 
+static int kvm_try_get_pfn(kvm_pfn_t pfn)
+{
+	if (kvm_is_reserved_pfn(pfn))
+		return 1;
+	return get_page_unless_zero(pfn_to_page(pfn));
+}
+
 static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 			       unsigned long addr, bool *async,
 			       bool write_fault, bool *writable,
@@ -1538,13 +1545,21 @@  static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 	 * Whoever called remap_pfn_range is also going to call e.g.
 	 * unmap_mapping_range before the underlying pages are freed,
 	 * causing a call to our MMU notifier.
+	 *
+	 * Certain IO or PFNMAP mappings can be backed with valid
+	 * struct pages, but be allocated without refcounting e.g.,
+	 * tail pages of non-compound higher order allocations, which
+	 * would then underflow the refcount when the caller does the
+	 * required put_page. Don't allow those pages here.
 	 */ 
-	kvm_get_pfn(pfn);
+	if (!kvm_try_get_pfn(pfn))
+		r = -EFAULT;
 
 out:
 	pte_unmap_unlock(ptep, ptl);
 	*p_pfn = pfn;
-	return 0;
+
+	return r;
 }
 
 /*