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

From: Mike Rapoport <rppt@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	Deepak Gupta <debug@rivosinc.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	"H.J. Lu" <hjl.tools@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3 11/36] arm64/mm: Map pages for guarded control stack
Date: Tue, 1 Aug 2023 20:02:31 +0300	[thread overview]
Message-ID: <20230801170231.GC2607694@kernel.org> (raw)
In-Reply-To: <20230731-arm64-gcs-v3-11-cddf9f980d98@kernel.org>

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@kernel.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.

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