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Re: [Xen-devel] [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option

On 07/27/2015 11:53 AM, Andy Lutomirski wrote:
On Mon, Jul 27, 2015 at 8:36 AM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx> wrote:
On 07/25/2015 01:36 AM, Andy Lutomirski wrote:
Here's v3.  It fixes the "dazed and confused" issue, I hope.  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 take a look at this?

Willy and Kees: I left the config option alone.  The -tiny people will
like it, and we can always add a sysctl of some sort later.

Changes from v3:
   - Hopefully fixed Xen.

32b-on-32b fails in the same manner. (but non-zero LDT is taken care of)

   - Fixed 32-bit test case on 32-bit native kernel.

I am not sure I see what changed.
I misplaced the fix in the wrong git commit, so I failed to sent it.  Oops.

I just sent v4.1 of patch 3.  Can you try that?

I am hitting BUG() in Xen code (returning from a hypercall) when freeing LDT in destroy_context(). Interestingly though when I run the test in the debugger I get SIGILL (just like before) but no BUG().

Let me get back to you on that later today.


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