Re: [Xen-devel] [PATCH v2 02/15] xen/arm: p2m: Use a whitelist rather than blacklist in get_page_from_gfn

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 28 Jul 2016, Julien Grall wrote:
> Currently, the check in get_page_from_gfn is using a blacklist. This is
> very fragile because we may forgot to update the check when a new p2m
> type is added.
> 
> To avoid any possible issue, use a whitelist. All type backed by a RAM
> page can could potential be valid. The check is borrowed from x86.
> 
> Note with this change, it is not possible anymore to retrieve a page when
> the p2m type is p2m_iommu_map_*. This is fine because they are special
> mappings for direct mapping workaround and the associated GFN should be
> used at all by callers of get_page_from_gfn.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Changes in v2:
>         - Update the commit message about iommu_mappings
> ---
>  xen/include/asm-arm/p2m.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
> index 3091c04..78d37ab 100644
> --- a/xen/include/asm-arm/p2m.h
> +++ b/xen/include/asm-arm/p2m.h
> @@ -104,9 +104,16 @@ typedef enum {
>  #define P2M_RAM_TYPES (p2m_to_mask(p2m_ram_rw) |        \
>                         p2m_to_mask(p2m_ram_ro))
>  
> +/* Grant mapping types, which map to a real frame in another VM */
> +#define P2M_GRANT_TYPES (p2m_to_mask(p2m_grant_map_rw) |  \
> +                         p2m_to_mask(p2m_grant_map_ro))
> +
>  /* Useful predicates */
>  #define p2m_is_ram(_t) (p2m_to_mask(_t) & P2M_RAM_TYPES)
>  #define p2m_is_foreign(_t) (p2m_to_mask(_t) & p2m_to_mask(p2m_map_foreign))
> +#define p2m_is_any_ram(_t) (p2m_to_mask(_t) &                   \
> +                            (P2M_RAM_TYPES | P2M_GRANT_TYPES |  \
> +                             p2m_to_mask(p2m_map_foreign)))
>  
>  static inline
>  void p2m_mem_access_emulate_check(struct vcpu *v,
> @@ -224,7 +231,7 @@ static inline struct page_info *get_page_from_gfn(
>      if (t)
>          *t = p2mt;
>  
> -    if ( p2mt == p2m_invalid || p2mt == p2m_mmio_direct )
> +    if ( !p2m_is_any_ram(p2mt) )
>          return NULL;
>  
>      if ( !mfn_valid(mfn) )
> -- 
> 1.9.1
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel