lkml.org 
[lkml]   [2014]   [Oct]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Xen-devel] [PATCH] xen: avoid writing to freed memory after race in p2m handling
On 14/10/14 10:00, Juergen Gross wrote:
> In case a race was detected during allocation of a new p2m tree
> element in alloc_p2m() the new allocated mid_mfn page is freed without
> updating the pointer to the found value in the tree. This will result
> in overwriting the just freed page with the mfn of the p2m leaf.

Can this race actually happen? i.e., does this need tagging for stable?

David

> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -566,6 +566,7 @@ static bool alloc_p2m(unsigned long pfn)
> /* Separately check the mid mfn level */
> unsigned long missing_mfn;
> unsigned long mid_mfn_mfn;
> + unsigned long old_mfn;
>
> mid_mfn = alloc_p2m_page();
> if (!mid_mfn)
> @@ -575,10 +576,13 @@ static bool alloc_p2m(unsigned long pfn)
>
> missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
> mid_mfn_mfn = virt_to_mfn(mid_mfn);
> - if (cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn) != missing_mfn)
> + old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
> + if (old_mfn != missing_mfn) {
> free_p2m_page(mid_mfn);
> - else
> + mid_mfn = mfn_to_virt(old_mfn);
> + } else {
> p2m_top_mfn_p[topidx] = mid_mfn;
> + }
> }
>
> if (p2m_top[topidx][mididx] == p2m_identity ||
>



\
 
 \ /
  Last update: 2014-10-14 12:01    [W:0.058 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site