linux-kernel - Re: [PATCH v6 20/41] x86/mm: Teach pte

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Message-ID: <63f28994.170a0220.e86dc.1134@mx.google.com>
Date:   Sun, 19 Feb 2023 12:41:55 -0800
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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com, debug@...osinc.com
Subject: Re: [PATCH v6 20/41] x86/mm: Teach pte_mkwrite() about stack memory

On Sat, Feb 18, 2023 at 01:14:12PM -0800, Rick Edgecombe wrote:
> If a VMA has the VM_SHADOW_STACK flag, it is shadow stack memory. So
> when it is made writable with pte_mkwrite(), it should create shadow
> stack memory, not conventionally writable memory. Now that pte_mkwrite()
> takes a VMA, and places where shadow stack memory might be created pass
> one, pte_mkwrite() can know when it should do this.
> 
> So make pte_mkwrite() create shadow stack memory when the VMA has the
> VM_SHADOW_STACK flag. Do the same thing for pmd_mkwrite().
> 
> This requires referencing VM_SHADOW_STACK in these functions, which are
> currently defined in pgtable.h, however mm.h (where VM_SHADOW_STACK is
> located) can't be pulled in without causing problems for files that
> reference pgtable.h. So also move pte/pmd_mkwrite() into pgtable.c, where
> they can safely reference VM_SHADOW_STACK.
> 
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

Is there any realistic performance impact from making these not inline
now?

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

-- 
Kees Cook