linux-kernel - Re: [PATCH PTI v3 01/10] x86/espfix/64: Fix espfix double-fault handling on 5-level systems

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Date:   Tue, 12 Dec 2017 20:18:50 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH PTI v3 01/10] x86/espfix/64: Fix espfix double-fault
 handling on 5-level systems

On Tue, Dec 12, 2017 at 07:56:36AM -0800, Andy Lutomirski wrote:
> Using PGDIR_SHIFT to identify espfix64 addresses on 5-level systems
> was wrong, and it resulted in panics due to unhandled double faults.
> Use P4D_SHIFT instead, which is correct on 4-level and 5-level
> machines.
> 
> This fixes a panic when running x86 selftests on 5-level machines.
> 
> Fixes: 1d33b219563f ("x86/espfix: Add support for 5-level paging")
> Cc: stable@...r.kernel.org
> Cc: "Kirill A. Shutemov" <kirill@...temov.name>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Thanks for catching this.

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

I remember that I tested espfix before and it was fine. That's strange.

With this patch on top of tip/WIP.x86/pti plus the change I've mentioned
before, sigreturn_64 doesn't crash qemu for me anymore.

-- 
 Kirill A. Shutemov