linux-kernel - Re: [PATCH v2 16/39] x86/mm: Update maybe

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Message-ID: <202210031122.A27CE24D39@keescook>
Date:   Mon, 3 Oct 2022 11:22:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 16/39] x86/mm: Update maybe_mkwrite() for shadow stack

On Thu, Sep 29, 2022 at 03:29:13PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> 
> When serving a page fault, maybe_mkwrite() makes a PTE writable if there is
> a write access to it, and its vma has VM_WRITE. Shadow stack accesses to
> shadow stack vma's are also treated as write accesses by the fault handler.
> This is because setting shadow stack memory makes it writable via some
> instructions, so COW has to happen even for shadow stack reads.
> 
> So maybe_mkwrite() should continue to set VM_WRITE vma's as normally
> writable, but also set VM_WRITE|VM_SHADOW_STACK vma's as shadow stack.
> 
> Do this by adding a pte_mkwrite_shstk() and a cross-arch stub. Check for
> VM_SHADOW_STACK in maybe_mkwrite() and call pte_mkwrite_shstk()
> accordingly.
> 
> Apply the same changes to maybe_pmd_mkwrite().
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook