| From: Jan Beulich <jbeulich@suse.com> |
| Subject: x86/shadow: fix refcount overflow check |
| |
| Commit c385d27079 ("x86 shadow: for multi-page shadows, explicitly track |
| the first page") reduced the refcount width to 25, without adjusting the |
| overflow check. Eliminate the disconnect by using a manifest constant. |
| |
| Interestingly, up to commit 047782fa01 ("Out-of-sync L1 shadows: OOS |
| snapshot") the refcount was 27 bits wide, yet the check was already |
| using 26. |
| |
| This is XSA-249. |
| |
| Signed-off-by: Jan Beulich <jbeulich@suse.com> |
| Reviewed-by: George Dunlap <george.dunlap@citrix.com> |
| Reviewed-by: Tim Deegan <tim@xen.org> |
| --- |
| v2: Simplify expression back to the style it was. |
| |
| --- a/xen/arch/x86/mm/shadow/private.h |
| +++ b/xen/arch/x86/mm/shadow/private.h |
| @@ -529,7 +529,7 @@ static inline int sh_get_ref(struct doma |
| x = sp->u.sh.count; |
| nx = x + 1; |
| |
| - if ( unlikely(nx >= 1U<<26) ) |
| + if ( unlikely(nx >= (1U << PAGE_SH_REFCOUNT_WIDTH)) ) |
| { |
| SHADOW_PRINTK("shadow ref overflow, gmfn=%lx smfn=%lx\n", |
| __backpointer(sp), mfn_x(smfn)); |
| --- a/xen/include/asm-x86/mm.h |
| +++ b/xen/include/asm-x86/mm.h |
| @@ -82,7 +82,8 @@ struct page_info |
| unsigned long type:5; /* What kind of shadow is this? */ |
| unsigned long pinned:1; /* Is the shadow pinned? */ |
| unsigned long head:1; /* Is this the first page of the shadow? */ |
| - unsigned long count:25; /* Reference count */ |
| +#define PAGE_SH_REFCOUNT_WIDTH 25 |
| + unsigned long count:PAGE_SH_REFCOUNT_WIDTH; /* Reference count */ |
| } sh; |
| |
| /* Page is on a free list: ((count_info & PGC_count_mask) == 0). */ |