linux-kernel - Re: [RFC PATCH v9 06/27] mm: Introduce VM

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Date:   Tue, 25 Feb 2020 12:07:50 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Yu-cheng Yu <yu-cheng.yu@...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>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack
 memory

On Wed, Feb 05, 2020 at 10:19:14AM -0800, Yu-cheng Yu wrote:
> A Shadow Stack (SHSTK) 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 and a new VM flag
> is necessary for tracking SHSTK VMAs.
> 
> v9:
> - Add VM_SHSTK case to arch_vma_name().
> - Revise the commit log to explain why a new VM flag is needed.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>

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

-Kees

> ---
>  arch/x86/mm/mmap.c | 2 ++
>  fs/proc/task_mmu.c | 3 +++
>  include/linux/mm.h | 8 ++++++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index aae9a933dfd4..482813b4c659 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -165,6 +165,8 @@ const char *arch_vma_name(struct vm_area_struct *vma)
>  {
>  	if (vma->vm_flags & VM_MPX)
>  		return "[mpx]";
> +	else if (vma->vm_flags & VM_SHSTK)
> +		return "[shadow stack]";
>  	return NULL;
>  }
>  
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9442631fd4af..590b58ee008a 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -687,6 +687,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>  		[ilog2(VM_PKEY_BIT4)]	= "",
>  #endif
>  #endif /* CONFIG_ARCH_HAS_PKEYS */
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +		[ilog2(VM_SHSTK)]	= "ss",
> +#endif
>  	};
>  	size_t i;
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cfaa8feecfe8..b5145fbe102e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -298,11 +298,13 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
>  #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
>  #define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
> +#define VM_HIGH_ARCH_BIT_5	37	/* bit only usable on 64-bit architectures */
>  #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
>  #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
>  #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
>  #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
>  #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
> +#define VM_HIGH_ARCH_5	BIT(VM_HIGH_ARCH_BIT_5)
>  #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
>  
>  #ifdef CONFIG_ARCH_HAS_PKEYS
> @@ -340,6 +342,12 @@ extern unsigned int kobjsize(const void *objp);
>  # define VM_MPX		VM_NONE
>  #endif
>  
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +# define VM_SHSTK	VM_HIGH_ARCH_5
> +#else
> +# define VM_SHSTK	VM_NONE
> +#endif
> +
>  #ifndef VM_GROWSUP
>  # define VM_GROWSUP	VM_NONE
>  #endif
> -- 
> 2.21.0
> 

-- 
Kees Cook