Re: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry

From: Andy Lutomirski
Date: Mon Sep 29 2014 - 16:29:47 EST

On Mon, Sep 29, 2014 at 1:01 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 09/29/2014 12:57 PM, Thomas Gleixner wrote:
>>> I think we should mask the bit anyway.
>> I tend to disagree. If we clear it there we need to consequentely
>> audit ALL other possibilites and if there are any we need to clear the
>> bit there as well. Just to make buggy user space happy?
> The entry options into the kernel are: interrupt/exception (already
> known to be OK),


I don't immediately see how to fix that without adding overhead.
Maybe do it in CLEAR_RREGS? This won't do any good if EFI ever starts
using IRET, though. We could suck it up and fix it on entry, adding
maybe ten cycles (wild guess).


This should happen for free if we fix SYSCALL64, I think.

Also, I thought entry_64.S was a mess. Eww, ia32entry.S.

I can try to write the patch later today. But I don't want to touch
the actual 32-bit kernel code -- I'll stick to the 64-bit native and
compat stuff, thanks.


and SYSCALL64. It is not too
> much to work through those issues, I don't think.
> -hpa

Andy Lutomirski
AMA Capital Management, LLC
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