linux-kernel - Re: [PATCH v3 11/36] arm64/mm: Map pages for guarded control stack

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Date:   Tue, 1 Aug 2023 20:02:31 +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 11/36] arm64/mm: Map pages for guarded control stack

On Mon, Jul 31, 2023 at 02:43:20PM +0100, Mark Brown wrote:
> Map pages flagged as being part of a GCS as such rather than using the
> full set of generic VM flags.
> 
> This is done using a conditional rather than extending the size of
> protection_map since that would make for a very sparse array.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/mm/mmap.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index 8f5b7ce857ed..e2ca770920ed 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -79,8 +79,23 @@ arch_initcall(adjust_protection_map);
>  
>  pgprot_t vm_get_page_prot(unsigned long vm_flags)
>  {
> -	pteval_t prot = pgprot_val(protection_map[vm_flags &
> +	pteval_t prot;
> +
> +	/*
> +	 * If this is a GCS then only interpret VM_WRITE.
> +	 *
> +	 * TODO: Just make protection_map[] bigger?  Nothing seems
> +	 * ideal here.
> +	 */

I think extending protection_map and updating adjust_protection_map() is
cleaner and probably faster.

> +	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
> +		if (vm_flags & VM_WRITE)
> +			prot = _PAGE_GCS;
> +		else
> +			prot = _PAGE_GCS_RO;
> +	} else {
> +		prot = pgprot_val(protection_map[vm_flags &
>  				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
> +	}
>  
>  	if (vm_flags & VM_ARM64_BTI)
>  		prot |= PTE_GP;
> 
> -- 
> 2.30.2
> 
> 

-- 
Sincerely yours,
Mike.