Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)

From: Andy Lutomirski
Date: Mon Mar 09 2015 - 14:36:41 EST

On Mon, Mar 9, 2015 at 11:16 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Mar 9, 2015 at 11:04 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> One option would be to change the NMI entry code to move itself down 8
>> bytes if this happens (came from kernel mode or sp == sp0 - 12,
>> perhaps).
> Hmm. That whole code currently depends on the stack setup being just a
> single instruction (the move to esp). And that simplifies things, I'd
> like to keep it that way.
> I'd *much* rather just keep the 8-byte padding. What was so
> problematic with that? It worked. It's been around forever. Removing
> it is the bug.

Let's at least fix it, then. processor.h has:

#define INIT_TSS { \
.x86_tss = { \
.sp0 = sizeof(init_stack) + (long)&init_stack, \

(moved in -tip)

That's bogus, and this bogosity is why I broke 32-bit -next in the
first place: I assumed it was correct.

I'll get it if no one beats me to it.


> Linus

Andy Lutomirski
AMA Capital Management, LLC
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