linux-kernel - Re: 32-bit PTI with THP = userspace corruption

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Message-ID: <20180831070722.wnulbbmillxkw7ke@suse.de>
Date:   Fri, 31 Aug 2018 09:07:22 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Meelis Roos <mroos@...ux.ee>
Cc:     Linux Kernel list <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 32-bit PTI with THP = userspace corruption

On Fri, Aug 31, 2018 at 07:12:44AM +0300, Meelis Roos wrote:
> > Thanks for the report! I'll try to reproduce the problem tomorrow and
> > investigate it. Can you please check if any of the kernel configurations
> > that show the bug has CONFIG_X86_PAE set? If not, can you please test
> > if enabling this option still triggers the problem?
> 
> Will check, but out of my memery there were 2 G3 HP Proliants that did 
> not fit into the pattern (problem did not appear). I have more than 4G 
> RAM in those and HIGHMEM_4G there, maybe that's it?

Yeah, I thought a bit about it, and for legacy paging the PMD paging
level is the root-level where we do the mirroring between kernel and
user page-table for PTI. This means we also need to collect A/D bits
from both entries, which we don't do yet.

But that all means it shouldn't happen with CONFIG_X86_PAE=y.

I'll try to reproduce and work on a fix.

Thanks,

	Joerg