Re: [Xen-devel] [PATCH v6 0/4] x86: modify_ldt improvement, test, and config option

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/31/2015 05:10 AM, Andrew Cooper wrote:
> On 30/07/15 22:31, Andy Lutomirski wrote:
> > This is intended for x86/urgent.  Sorry for taking so long, but it
> > seemed nice to avoid breaking Xen.
> Very much appreciated.  Thanks!
>
> > This fixes the "dazed and confused" issue which was exposed by the
> > CVE-2015-5157 fix.  It's also probably a good general attack surface
> > reduction, and it replaces some scary code with IMO less scary code.
> >
> > Also, servers and embedded systems should probably turn off modify_ldt.
> > This makes that possible.
> >
> > Xen people, can you test patch 1?  It works for me on my evil 32-bit
> > Xen virtio setup.
> So the LDT issue seems to have gone away, which is good.
>
> However, I did get this from my single vcpu guest test
>
> [OK]    LDT entry 0 is invalid
> [SKIP]    Cannot set affinity to CPU 1
> [RUN]    Test exec
> [    3.638967] CPU 0 set the LDT
> [OK]    LDT entry 0 has AR 0x0040FA00 and limit 0x0000002A
> [    3.639380] ------------[ cut here ]------------
> [    3.639389] WARNING: CPU: 0 PID: 383 at
> /local/linux-mainline.git/arch/x86/include/asm/mmu_context.h:96
> flush_old_exec+0x7fd/0xb70()
> [    3.639397] DEBUG_LOCKS_WARN_ON(!irqs_disabled())
You must be running v5 (or earlier). This is fixed in v6 --- it is now 
'DEBUG_LOCKS_WARN_ON(preemptible());'

-boris

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