From: Andy Lutomirski
> Sent: 12 December 2017 19:27
...
> > Why is the iret exception unrecoverable anyway? Does anybody even know?
> >
>
> Weird microcode shit aside, a fault on IRET will return to kernel code with
> kernel GS, and then the
> next time we enter the kernel we're backwards. We c
> On Dec 12, 2017, at 11:05 AM, Linus Torvalds
> wrote:
>
>> On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
>>
>> There is one exception; IRET will immediately load CS/SS and unrecoverably
>> #GP. To avoid this issue access the LDT descriptors used by CS/SS before
>> the IRET to use
On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
>
> There is one exception; IRET will immediately load CS/SS and unrecoverably
> #GP. To avoid this issue access the LDT descriptors used by CS/SS before
> the IRET to userspace.
Ok, so the other patch made me nervous, this just makes me go
On Tue, Dec 12, 2017 at 07:41:39PM +0100, Thomas Gleixner wrote:
> The pages are populated _before_ the new ldt is installed. So no memory
> pressure issue, nothing. If the populate fails, then modify_ldt() returns
> with an error.
Also, these pages are not visible to reclaim. They're not pagecach
On Tue, 12 Dec 2017, Peter Zijlstra wrote:
> On Tue, Dec 12, 2017 at 10:22:48AM -0800, Andy Lutomirski wrote:
> >
> > Also, why is LAR deferred to user exit? And I thought that LAR didn't
> > set the accessed bit.
>
> LAR does not set the ACCESSED bit indeed, we need to explicitly set that
> wh
On Tue, Dec 12, 2017 at 10:22:48AM -0800, Andy Lutomirski wrote:
>
> Also, why is LAR deferred to user exit? And I thought that LAR didn't
> set the accessed bit.
LAR does not set the ACCESSED bit indeed, we need to explicitly set that
when creating the descriptor.
It also works if you do the L
> On Dec 12, 2017, at 10:10 AM, Andy Lutomirski wrote:
>
>> On Tue, Dec 12, 2017 at 10:09 AM, Peter Zijlstra
>> wrote:
>>> On Tue, Dec 12, 2017 at 10:03:02AM -0800, Andy Lutomirski wrote:
>>> On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
>>
@@ -171,6 +172,9 @@ static void exi
On Tue, Dec 12, 2017 at 10:09 AM, Peter Zijlstra wrote:
> On Tue, Dec 12, 2017 at 10:03:02AM -0800, Andy Lutomirski wrote:
>> On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
>
>> > @@ -171,6 +172,9 @@ static void exit_to_usermode_loop(struct
>> > /* Disable IRQs and retry
On Tue, Dec 12, 2017 at 10:03:02AM -0800, Andy Lutomirski wrote:
> On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
> > @@ -171,6 +172,9 @@ static void exit_to_usermode_loop(struct
> > /* Disable IRQs and retry */
> > local_irq_disable();
> >
> > +
On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote:
> From: Peter Zijlstra
>
> When mapping the LDT RO the hardware will typically generate write faults
> on first use. These faults can be trapped and the backing pages can be
> modified by the kernel.
>
> There is one exception; IRET will imm
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