linux-kernel - Re: [PATCH RFC RFT v2 1/5] mm: Introduce ARCH_HAS_USER_SHADOW

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Date:   Wed, 15 Nov 2023 16:12:50 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mark Brown <broonie@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Kees Cook <keescook@...omium.org>, jannh@...gle.com,
        linux-kselftest@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH RFC RFT v2 1/5] mm: Introduce ARCH_HAS_USER_SHADOW_STACK

On 14.11.23 21:05, Mark Brown wrote:
> Since multiple architectures have support for shadow stacks and we need to
> select support for this feature in several places in the generic code
> provide a generic config option that the architectures can select.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>   arch/x86/Kconfig   | 1 +
>   fs/proc/task_mmu.c | 2 +-
>   include/linux/mm.h | 2 +-
>   mm/Kconfig         | 6 ++++++
>   4 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3762f41bb092..14b7703a9a2b 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1952,6 +1952,7 @@ config X86_USER_SHADOW_STACK
>   	depends on AS_WRUSS
>   	depends on X86_64
>   	select ARCH_USES_HIGH_VMA_FLAGS
> +	select ARCH_HAS_USER_SHADOW_STACK
>   	select X86_CET
>   	help
>   	  Shadow stack protection is a hardware feature that detects function
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index ef2eb12906da..f0a904aeee8e 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -699,7 +699,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>   #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
>   		[ilog2(VM_UFFD_MINOR)]	= "ui",
>   #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
> -#ifdef CONFIG_X86_USER_SHADOW_STACK
> +#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
>   		[ilog2(VM_SHADOW_STACK)] = "ss",
>   #endif
>   	};
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 418d26608ece..10462f354614 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -341,7 +341,7 @@ extern unsigned int kobjsize(const void *objp);
>   #endif
>   #endif /* CONFIG_ARCH_HAS_PKEYS */
>   
> -#ifdef CONFIG_X86_USER_SHADOW_STACK
> +#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
>   /*
>    * VM_SHADOW_STACK should not be set with VM_SHARED because of lack of
>    * support core mm.
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 89971a894b60..b8638da636e1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1270,6 +1270,12 @@ config LOCK_MM_AND_FIND_VMA
>   	bool
>   	depends on !STACK_GROWSUP
>   
> +config ARCH_HAS_USER_SHADOW_STACK
> +	bool
> +	help
> +	  The architecture has hardware support for userspace shadow call
> +          stacks (eg, x86 CET, arm64 GCS, RISC-V Zisslpcfi).
> +

Probably less controversial if we start with one example we have in 
place: "e.g., x86 CET". That should be sufficient to understand what 
this is about :)

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb