linux-kernel - Re: [PATCH v4 3/5] x86, entry: Switch stacks on a paranoid entry from userspace

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Message-ID: <20141124155512.GD20296@pd.tnic>
Date:	Mon, 24 Nov 2014 16:55:13 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v4 3/5] x86, entry: Switch stacks on a paranoid entry
 from userspace

On Fri, Nov 21, 2014 at 01:26:09PM -0800, Andy Lutomirski wrote:
> This causes all non-NMI, non-double-fault kernel entries from
> userspace to run on the normal kernel stack.  Double-fault is
> exempt to minimize confusion if we double-fault directly from
> userspace due to a bad kernel stack.
> 
> This is, suprisingly, simpler and shorter than the current code.  It
> removes the IMO rather frightening paranoid_userspace path, and it
> make sync_regs much simpler.
> 
> There is no risk of stack overflow due to this change -- the kernel
> stack that we switch to is empty.
> 
> This will also enable us to create non-atomic sections within
> machine checks from userspace, which will simplify memory failure
> handling.  It will also allow the upcoming fsgsbase code to be
> simplified, because it doesn't need to worry about usergs when
> scheduling in paranoid_exit, as that code no longer exists.
> 
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Andy Lutomirski <luto@...capital.net>

Acked-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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