linux-kernel - Re: [PATCH 14/43] x86/entry/64: Return to userspace from the trampoline stack

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Date:   Fri, 24 Nov 2017 14:46:14 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ingo Molnar <mingo@...nel.org>
cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 14/43] x86/entry/64: Return to userspace from the trampoline
 stack

On Fri, 24 Nov 2017, Ingo Molnar wrote:

> From: Andy Lutomirski <luto@...nel.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@...nel.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>