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

[Ian Campbell <ian.campbell@citrix.com>]

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