linux-kernel - Re: [PATCH v3 10/36] mm: Define VM_SHADOW

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Date:   Tue, 1 Aug 2023 19:53:12 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 10/36] mm: Define VM_SHADOW_STACK for arm64 when we
 support GCS

On Mon, Jul 31, 2023 at 02:43:19PM +0100, Mark Brown wrote:
> Use VM_HIGH_ARCH_5 for guarded control stack pages.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  Documentation/filesystems/proc.rst |  2 +-
>  fs/proc/task_mmu.c                 |  3 +++
>  include/linux/mm.h                 | 12 +++++++++++-
>  3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 6ccb57089a06..086a0408a4d7 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -566,7 +566,7 @@ 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
> +    ss    shadow/guarded control stack page

I've missed this in Rick's patches, but it's not a page but area.

>      ==    =======================================
>  
>  Note that there is no guarantee that every flag and associated mnemonic will
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index cfab855fe7e9..e8c50848bb16 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -711,6 +711,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>  #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>  #ifdef CONFIG_X86_USER_SHADOW_STACK
>  		[ilog2(VM_SHADOW_STACK)] = "ss",
> +#endif
> +#ifdef CONFIG_ARM64_GCS
> +		[ilog2(VM_SHADOW_STACK)] = "ss",
>  #endif
>  	};
>  	size_t i;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 43fe625b85aa..3f939ae212e5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -372,7 +372,17 @@ extern unsigned int kobjsize(const void *objp);
>   * having a PAGE_SIZE guard gap.
>   */
>  # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> -#else
> +#endif
> +
> +#if defined(CONFIG_ARM64_GCS)
> +/*
> + * arm64's Guarded Control Stack implements similar functionality and
> + * has similar constraints to shadow stacks.
> + */
> +# define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> +#endif
> +
> +#ifndef VM_SHADOW_STACK
>  # define VM_SHADOW_STACK	VM_NONE
>  #endif
>  
> 
> -- 
> 2.30.2
> 
> 

-- 
Sincerely yours,
Mike.