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

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
[    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());'


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