Re: [tip:x86/security] x86: Add NX protection for kernel data

[Konrad Rzeszutek Wilk]

On Fri, Jan 14, 2011 at 03:15:30PM -0500, Konrad Rzeszutek Wilk wrote:
> On Tue, Jan 11, 2011 at 03:31:35PM -0800, Kees Cook wrote:
> > On Thu, Nov 18, 2010 at 02:08:22PM +0000, tip-bot for Matthieu Castet wrote:
> > > Commit-ID:  5bd5a452662bc37c54fb6828db1a3faf87e6511c
> > > Gitweb:     http://git.kernel.org/tip/5bd5a452662bc37c54fb6828db1a3faf87e6511c
> > > Author:     Matthieu Castet <castet.matthieu@xxxxxxx>
> > > AuthorDate: Tue, 16 Nov 2010 22:31:26 +0100
> > > Committer:  Ingo Molnar <mingo@xxxxxxx>
> > > CommitDate: Thu, 18 Nov 2010 12:52:04 +0100
> > > 
> > > x86: Add NX protection for kernel data
> > 
> > [I'd sent this in reply to the wrong patch before, resending now...]
> > 
> > Hi,
> > 
> > I was just shown this[1] on Xen from an Ubuntu bug report[2].
> > 
> > [    1.230382] NX-protecting the kernel data: 3884k
> > [    1.231002] BUG: unable to handle kernel paging request at c1782ae0
> > ...
> > [    1.231145] Call Trace:
> > [    1.231152]  [<c0138481>] ? __change_page_attr+0x2c1/0x370
> > [    1.231161]  [<c02163a1>] ? __purge_vmap_area_lazy+0xc1/0x180
> > [    1.231169]  [<c013857c>] ? __change_page_attr_set_clr+0x4c/0xb0
> > [    1.231176]  [<c0138838>] ? change_page_attr_set_clr+0x128/0x300
> > [    1.231183]  [<c010798e>] ? __raw_callee_save_xen_restore_fl+0x6/0x8
> > [    1.231192]  [<c0159ca1>] ? vprintk+0x171/0x3f0
> > [    1.231198]  [<c0138bdf>] ? set_memory_nx+0x5f/0x70
> 
> If you run it with Xen debugging enabled:
> 
> [    7.753329] NX-protecting the kernel data: 2400k
> (XEN) mm.c:2389:d0 Bad type (saw 3c000003 != exp 70000000) for mfn 1355a5 (pfn 15a5)
> (XEN) mm.c:889:d0 Error getting mfn 1355a5 (pfn 15a5) from L1 entry 80000001355a5063 for l1e_owner=0, pg_owner=0
> (XEN) mm.c:4958:d0 ptwr_emulate: could not get_page_from_l1e()
> [    7.759087] BUG: unable to handle kernel paging request at c82a4d28
> [    7.759087] IP: [<c100608c>] xen_set_pte_atomic+0x21/0x2f
> [    7.759087] *pdpt = 0000000001663001 *pde = 00000000082db067 *pte = 80000000082a4061 
> .. and same stack trace.
> 
> > 
> > 
> > Does Xen have different size page table allocations or something weird?
> 
> The same page size. Not sure actually why it is being triggered. Let me copy
> Keir on this. Keir, the region that is being marked as _NX is .bss one and

Um, it actually is from _etext -> __init_end + HPAGE_SIZE.

instrumenting the code a bit shows that setting of RW+NX from _etext throgh
__init_end works just fine. It just when you start at the PFN _past_ the
__init_end it dies. Any ideas? 

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