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

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Message-ID: <80dbcf02-2035-94dc-ca29-4f17ad271fda@linux.intel.com>
Date:   Fri, 5 Jan 2018 23:55:38 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Hanjun Guo <guohanjun@...wei.com>, Jiri Kosina <jikos@...nel.org>
Cc:     Yisheng Xie <xieyisheng1@...wei.com>, linux-kernel@...r.kernel.org,
        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,
        Linus Torvalds <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 01/05/2018 10:53 PM, Hanjun Guo wrote:
>>  +	/*
>>  +	 * PTI poisons low addresses in the kernel page tables in the
>>  +	 * name of making them unusable for userspace.  To execute
>>  +	 * code at such a low address, the poison must be cleared.
>>  +	 */
>>  +	pgd->pgd &= ~_PAGE_NX;
>>
>> We will have a try in a minute, and report back later.
> And it works，we can boot/reboot the system successfully, thank
> you all the quick response and debug!

I think I'll just submit the attached patch if there are no objections
(and if it works, of course!).

I just stuck the NX clearing at the bottom.

View attachment "pti-tboot-fix.patch" of type "text/x-patch" (1450 bytes)