linux-kernel - Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)

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Date:   Thu, 4 Jan 2018 22:29:53 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Yisheng Xie <xieyisheng1@...wei.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, richard.fellner@...dent.tugraz.at,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, luto@...nel.org,
        torvalds@...ux-foundation.org, keescook@...gle.com,
        hughd@...gle.com, x86@...nel.org,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page
 tables (core patch)

On 01/04/2018 10:16 PM, Yisheng Xie wrote:
> BTW, we have just reported a bug caused by kaiser[1], which looks like
> caused by SMEP. Could you please help to have a look?
> 
> [1] https://lkml.org/lkml/2018/1/5/3

Please report that to your kernel vendor.  Your EFI page tables have the
NX bit set on the low addresses.  There have been a bunch of iterations
of this, but you need to make sure that the EFI kernel mappings don't
get _PAGE_NX set on them.  Look at what __pti_set_user_pgd() does in
mainline.