* [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access
@ 2016-01-26 11:46 Corneliu ZUZU
2016-01-26 16:14 ` Ian Campbell
2016-02-03 11:37 ` [PATCH v2] " Corneliu ZUZU
0 siblings, 2 replies; 6+ messages in thread
From: Corneliu ZUZU @ 2016-01-26 11:46 UTC (permalink / raw)
To: xen-devel; +Cc: Stefano Stabellini, Ian Campbell
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.
Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
---
xen/arch/arm/p2m.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 2190908..a9157e5 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -490,7 +490,7 @@ 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;
--
2.5.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access
2016-01-26 11:46 [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access Corneliu ZUZU
@ 2016-01-26 16:14 ` Ian Campbell
[not found] ` <56A89338.8040409@bitdefender.com>
2016-02-03 11:37 ` [PATCH v2] " Corneliu ZUZU
1 sibling, 1 reply; 6+ messages in thread
From: Ian Campbell @ 2016-01-26 16:14 UTC (permalink / raw)
To: Corneliu ZUZU, xen-devel; +Cc: Stefano Stabellini
On Tue, 2016-01-26 at 13:46 +0200, Corneliu ZUZU wrote:
> 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
What about:
-> p2m_mem_access_check
-> p2m_get_mem_access
I can't see the lock being taken in that paths.
As well as fixing that I think it would be wise to add an assert that the
lock is held before the call to p2m_lookup which you are changing into the
unlocked variant.
>
> 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.
>
> Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
> ---
> xen/arch/arm/p2m.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 2190908..a9157e5 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -490,7 +490,7 @@ 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
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access
2016-01-26 11:46 [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access Corneliu ZUZU
2016-01-26 16:14 ` Ian Campbell
@ 2016-02-03 11:37 ` Corneliu ZUZU
2016-02-03 11:52 ` Ian Campbell
1 sibling, 1 reply; 6+ messages in thread
From: Corneliu ZUZU @ 2016-02-03 11:37 UTC (permalink / raw)
To: xen-devel; +Cc: Stefano Stabellini, Ian Campbell
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;
--
2.5.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access
2016-02-03 11:37 ` [PATCH v2] " Corneliu ZUZU
@ 2016-02-03 11:52 ` Ian Campbell
2016-02-03 11:56 ` Corneliu ZUZU
0 siblings, 1 reply; 6+ messages in thread
From: Ian Campbell @ 2016-02-03 11:52 UTC (permalink / raw)
To: Corneliu ZUZU, xen-devel; +Cc: Stefano Stabellini
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access
2016-02-03 11:52 ` Ian Campbell
@ 2016-02-03 11:56 ` Corneliu ZUZU
0 siblings, 0 replies; 6+ messages in thread
From: Corneliu ZUZU @ 2016-02-03 11:56 UTC (permalink / raw)
To: xen-devel
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.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2016-02-03 11:56 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-01-26 11:46 [PATCH] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access Corneliu ZUZU
2016-01-26 16:14 ` Ian Campbell
[not found] ` <56A89338.8040409@bitdefender.com>
2016-01-27 11:42 ` Ian Campbell
2016-02-03 11:37 ` [PATCH v2] " Corneliu ZUZU
2016-02-03 11:52 ` Ian Campbell
2016-02-03 11:56 ` Corneliu ZUZU
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