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Date: Sun, 26 Nov 2017 15:18:47 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 14/43] x86/asm/64: Return to userspace from the
 trampoline stack
Message-ID: <20171126141847.mgn6lnsuafloasyc@gmail.com>
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 <20171124191005.bn4zchmxlngdhvpv@pd.tnic>
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* Borislav Petkov <bp@alien8.de> wrote:

> On Fri, Nov 24, 2017 at 06:23:42PM +0100, Ingo Molnar wrote:
> > From: Andy Lutomirski <luto@kernel.org>
> > 
> > By itself, this is useless.  It gives us the ability to run some final
> > code before exit that cannnot run on the kernel stack.  This could
> > include a CR3 switch a la KAISER or some kernel stack erasing, for
> > example.  (Or even weird things like *changing* which kernel stack
> > gets used as an ASLR-strengthening mechanism.)
> > 
> > The SYSRET32 path is not covered yet.  It could be in the future or
> > we could just ignore it and force the slow path if needed.
> > 
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Borislav Petkov <bpetkov@suse.de>
> > Cc: Brian Gerst <brgerst@gmail.com>
> > Cc: Dave Hansen <dave.hansen@intel.com>
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Link: https://lkml.kernel.org/r/d350017000eed20922c3b2711a2d9229dc809256.1511497875.git.luto@kernel.org
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > ---
> >  arch/x86/entry/entry_64.S | 55 +++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 51 insertions(+), 4 deletions(-)
> 
> Nice commenting, future generations will appreciate it!
> 
> :-)
> 
> Reviewed-by: Borislav Petkov <bp@suse.de>

Heh, indeed - if by 'future generations' you mean 'the guys who merge it,
a few months down the line'. ;-)

Thanks,

	Ingo