linux-kernel - Re: [PATCH v2 14/39] mm: Introduce VM_SHADOW

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Message-ID: <202210031113.FCBAD74@keescook>
Date:   Mon, 3 Oct 2022 11:17:10 -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 14/39] mm: Introduce VM_SHADOW_STACK for shadow stack
 memory

On Thu, Sep 29, 2022 at 03:29:11PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> 
> A shadow stack PTE must be read-only and have _PAGE_DIRTY set.  However,
> read-only and Dirty PTEs also exist for copy-on-write (COW) pages.  These
> two cases are handled differently for page faults. Introduce
> VM_SHADOW_STACK to track shadow stack VMAs.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>  Documentation/filesystems/proc.rst | 1 +
>  arch/x86/mm/mmap.c                 | 2 ++
>  fs/proc/task_mmu.c                 | 3 +++
>  include/linux/mm.h                 | 8 ++++++++
>  4 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index e7aafc82be99..d54ff397947a 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -560,6 +560,7 @@ encoded manner. The codes are the following:
>      mt    arm64 MTE allocation tags are enabled
>      um    userfaultfd missing tracking
>      uw    userfaultfd wr-protect tracking
> +    ss    shadow stack page
>      ==    =======================================
>  
>  Note that there is no guarantee that every flag and associated mnemonic will
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index c90c20904a60..f3f52c5e2fd6 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -165,6 +165,8 @@ unsigned long get_mmap_base(int is_legacy)
>  
>  const char *arch_vma_name(struct vm_area_struct *vma)
>  {
> +	if (vma->vm_flags & VM_SHADOW_STACK)
> +		return "[shadow stack]";
>  	return NULL;
>  }

I agree with Kirill: this should be in the arch-agnostic code.

-- 
Kees Cook