linux-kernel - Re: [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB Shadow Stack page fault

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Date:   Fri, 13 Mar 2020 15:00:20 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB Shadow Stack page
 fault

On Tue, 2020-02-25 at 12:59 -0800, Kees Cook wrote:
> On Wed, Feb 05, 2020 at 10:19:23AM -0800, Yu-cheng Yu wrote:
> > This patch implements THP Shadow Stack (SHSTK) copying in the same way as
> > in the previous patch for regular PTE.
> > 
> > In copy_huge_pmd(), clear the dirty bit from the PMD to cause a page fault
> > upon the next SHSTK access to the PMD.  At that time, fix the PMD and
> > copy/re-use the page.
> 
> Now is as good a time as any to ask: do you have selftests for all this?
> It seems like it would be really nice to have a way to verify SHSTK is
> working correctly.

Yes, I have some simple tests at https://github.com/yyu168/cet-smoke-test.
I also run Linux/tools/testing/selftests/x86 and GLIBC tests with CET and THP
combinations.

Yu-cheng