On Fri, 2015-05-15 at 15:38 +0200, Willy Tarreau wrote:
> Hi Ben,
>
> On Fri, May 15, 2015 at 01:32:20PM +0100, Ben Hutchings wrote:
> > On Fri, 2015-05-15 at 10:05 +0200, Willy Tarreau wrote:
> > > 2.6.32-longterm review patch. If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > From: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> > >
> > > commit f647d7c155f069c1a068030255c300663516420e upstream.
> > >
> > > Otherwise, if buggy user code points DS or ES into the TLS
> > > array, they would be corrupted after a context switch.
> > >
> > > This also significantly improves the comments and documents some
> > > gotchas in the code.
> > >
> > > Before this patch, the both tests below failed. With this
> > > patch, the es test passes, although the gsbase test still fails.
> > [...]
> >
> > This depends on the changes to FPU/MMX/SSE state management that you
> > didn't apply to 2.6.32. Note this comment:
> >
> > /* Must be after DS reload */
> > unlazy_fpu(prev_p);
>
> Are you sure you're not confusing with another one ? When running
> estest without this patch, I get "FAIL: ES corrupted 1000/1000 times"
> while I get "OK: ES was preserved" once applied, so it does seem to
> do what it's intended for.
>
> Also I'm not seeing any reference to the comment above in the patch
> nor around it, which leaves me confused :-/
v2.6.32.65:arch/x86/kernel/process_64.c:425: /* Must be after DS reload */
If this comment is correct then the patch will cause a regression for
FPU state management. The comment was introduced by:
commit 0a5ace2ab08d45cd78d7ef0067cdcd5c812ac54f
Author: Andi Kleen <ak@xxxxxxx>
Date: Thu Oct 5 18:47:22 2006 +0200
[PATCH] x86-64: Fix FPU corruption
Ben.
--
Ben Hutchings
It is impossible to make anything foolproof because fools are so ingenious.
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