diff mbox

[v2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access

Message ID 1454499464-7278-1-git-send-email-czuzu@bitdefender.com
State New, archived
Headers show

Commit Message

Corneliu ZUZU Feb. 3, 2016, 11:37 a.m. UTC
When __p2m_get_mem_access gets called, the p2m lock is already taken
by either get_page_from_gva or p2m_get_mem_access.
Possible code paths:
1)	-> get_page_from_gva
		-> p2m_mem_access_check_and_get_page
			-> __p2m_get_mem_access
2)	-> p2m_get_mem_access
		-> __p2m_get_mem_access

In both cases if __p2m_get_mem_access subsequently gets to
call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
hang will occur, since p2m_lookup also spin-locks on the p2m lock.

This bug-fix simply replaces the p2m_lookup call from __p2m_get_mem_access
with a call to __p2m_lookup and also adds an ASSERT to ensure that the p2m lock
is already taken upon __p2m_get_mem_access entry.

Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>

---
Changed since v1:
  * added p2m-lock ASSERT
---
 xen/arch/arm/p2m.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Ian Campbell Feb. 3, 2016, 11:52 a.m. UTC | #1
On Wed, 2016-02-03 at 13:37 +0200, Corneliu ZUZU wrote:

I just now applied a previous v2 which was already in my queue. Was this
just an accidental resend of v2 or is there some important change and this
is really a v3?

> When __p2m_get_mem_access gets called, the p2m lock is already taken
> by either get_page_from_gva or p2m_get_mem_access.
> Possible code paths:
> 1)	-> get_page_from_gva
> 		-> p2m_mem_access_check_and_get_page
> 			-> __p2m_get_mem_access
> 2)	-> p2m_get_mem_access
> 		-> __p2m_get_mem_access
> 
> In both cases if __p2m_get_mem_access subsequently gets to
> call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
> hang will occur, since p2m_lookup also spin-locks on the p2m lock.
> 
> This bug-fix simply replaces the p2m_lookup call from
> __p2m_get_mem_access
> with a call to __p2m_lookup and also adds an ASSERT to ensure that the
> p2m lock
> is already taken upon __p2m_get_mem_access entry.
> 
> Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
> 
> ---
> Changed since v1:
>   * added p2m-lock ASSERT
> ---
>  xen/arch/arm/p2m.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 2190908..e8e6db4 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -468,6 +468,8 @@ static int __p2m_get_mem_access(struct domain *d,
> gfn_t gfn,
>  #undef ACCESS
>      };
>  
> +    ASSERT(spin_is_locked(&p2m->lock));
> +
>      /* If no setting was ever set, just return rwx. */
>      if ( !p2m->mem_access_enabled )
>      {
> @@ -490,7 +492,7 @@ static int __p2m_get_mem_access(struct domain *d,
> gfn_t gfn,
>           * No setting was found in the Radix tree. Check if the
>           * entry exists in the page-tables.
>           */
> -        paddr_t maddr = p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
> +        paddr_t maddr = __p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
>          if ( INVALID_PADDR == maddr )
>              return -ESRCH;
>
Corneliu ZUZU Feb. 3, 2016, 11:56 a.m. UTC | #2
On 2/3/2016 1:52 PM, Ian Campbell wrote:
> On Wed, 2016-02-03 at 13:37 +0200, Corneliu ZUZU wrote:
>
> I just now applied a previous v2 which was already in my queue. Was this
> just an accidental resend of v2 or is there some important change and this
> is really a v3?
>
>> When __p2m_get_mem_access gets called, the p2m lock is already taken
>> by either get_page_from_gva or p2m_get_mem_access.
>> Possible code paths:
>> 1)	-> get_page_from_gva
>> 		-> p2m_mem_access_check_and_get_page
>> 			-> __p2m_get_mem_access
>> 2)	-> p2m_get_mem_access
>> 		-> __p2m_get_mem_access
>>
>> In both cases if __p2m_get_mem_access subsequently gets to
>> call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
>> hang will occur, since p2m_lookup also spin-locks on the p2m lock.
>>
>> This bug-fix simply replaces the p2m_lookup call from
>> __p2m_get_mem_access
>> with a call to __p2m_lookup and also adds an ASSERT to ensure that the
>> p2m lock
>> is already taken upon __p2m_get_mem_access entry.
>>
>> Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
>>
>> ---
>> Changed since v1:
>>    * added p2m-lock ASSERT
>> ---
>>   xen/arch/arm/p2m.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>> index 2190908..e8e6db4 100644
>> --- a/xen/arch/arm/p2m.c
>> +++ b/xen/arch/arm/p2m.c
>> @@ -468,6 +468,8 @@ static int __p2m_get_mem_access(struct domain *d,
>> gfn_t gfn,
>>   #undef ACCESS
>>       };
>>   
>> +    ASSERT(spin_is_locked(&p2m->lock));
>> +
>>       /* If no setting was ever set, just return rwx. */
>>       if ( !p2m->mem_access_enabled )
>>       {
>> @@ -490,7 +492,7 @@ static int __p2m_get_mem_access(struct domain *d,
>> gfn_t gfn,
>>            * No setting was found in the Radix tree. Check if the
>>            * entry exists in the page-tables.
>>            */
>> -        paddr_t maddr = p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
>> +        paddr_t maddr = __p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
>>           if ( INVALID_PADDR == maddr )
>>               return -ESRCH;
>>   
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
No, sorry, this is just a duplicate of the 1st v2, I thought the first 
one was not sent properly (after waiting a few days and noticing
I was no longer finding it on the web).
Ignore this one. And thanks.

Corneliu.
diff mbox

Patch

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 2190908..e8e6db4 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -468,6 +468,8 @@  static int __p2m_get_mem_access(struct domain *d, gfn_t gfn,
 #undef ACCESS
     };
 
+    ASSERT(spin_is_locked(&p2m->lock));
+
     /* If no setting was ever set, just return rwx. */
     if ( !p2m->mem_access_enabled )
     {
@@ -490,7 +492,7 @@  static int __p2m_get_mem_access(struct domain *d, gfn_t gfn,
          * No setting was found in the Radix tree. Check if the
          * entry exists in the page-tables.
          */
-        paddr_t maddr = p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
+        paddr_t maddr = __p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
         if ( INVALID_PADDR == maddr )
             return -ESRCH;