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Re: [Xen-devel] [PATCH v3 1/3] x86/ldt: Make modify_ldt synchronous
- To: Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Sat, 25 Jul 2015 00:13:23 -0400
- Cc: "security@xxxxxxxxxx" <security@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, X86 ML <x86@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, stable@xxxxxxxxxxxxxxx, xen-devel <xen-devel@xxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Sasha Levin <sasha.levin@xxxxxxxxxx>
- Delivery-date: Sat, 25 Jul 2015 04:14:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 07/22/2015 06:20 PM, Boris Ostrovsky wrote:
On 07/22/2015 03:23 PM, Andy Lutomirski wrote:
+ error = -ENOMEM;
+ new_ldt = alloc_ldt_struct(newsize);
+ if (!new_ldt)
goto out_unlock;
- }
- fill_ldt(&ldt, &ldt_info);
- if (oldmode)
- ldt.avl = 0;
+ if (old_ldt) {
+ memcpy(new_ldt->entries, old_ldt->entries,
+ oldsize * LDT_ENTRY_SIZE);
+ }
+ memset(new_ldt->entries + oldsize * LDT_ENTRY_SIZE, 0,
+ (newsize - oldsize) * LDT_ENTRY_SIZE);
We need to zero out full page (probably better in alloc_ldt_struct()
with vmzalloc/__GFP_ZERO) --- Xen checks whole page that is assigned
to G/LDT and gets unhappy if an invalid descriptor is found there.
This fixes one problem. There is something else that Xen gets upset
about, I haven't figured what it is yet (and I am out tomorrow so it
may need to wait until Friday).
What I thought was another problem turned out not to be one so both 64-
and 32-bit tests passed on 64-bit PV (when allocated LDT is zeroed out)
However, on 32-bit kernel the test is failing multicpu test, I don't
know yet what it is.
-boris
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