linux-kernel - Re: [PATCH v2 19/39] mm/mmap: Add shadow stack pages to memory accounting

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Date:   Tue, 4 Oct 2022 03:03:36 +0300
From:   "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
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>,
        Kees Cook <keescook@...omium.org>,
        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>,
        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 19/39] mm/mmap: Add shadow stack pages to memory
 accounting

On Thu, Sep 29, 2022 at 03:29:16PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> 
> Account shadow stack pages to stack memory.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
> 
> ---
> 
> v2:
>  - Remove is_shadow_stack_mapping() and just change it to directly bitwise
>    and VM_SHADOW_STACK.
> 
> Yu-cheng v26:
>  - Remove redundant #ifdef CONFIG_MMU.
> 
> Yu-cheng v25:
>  - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for is_shadow_stack_mapping().
> 
>  mm/mmap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f0d2e9143bd0..8569ef09614c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1682,6 +1682,9 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
>  	if (file && is_file_hugepages(file))
>  		return 0;
>  
> +	if (vm_flags & VM_SHADOW_STACK)
> +		return 1;
> +
>  	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;

Hm. Isn't the last check true for shadow stack too? IIUC, shadow stack has
VM_WRITE set, so accountable_mapping() should work correctly as is.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov