Re: [PATCH v8 27/28] arm64: mte: Kconfig entry

[Randy Dunlap <rdunlap@infradead.org>]

Hi,

On 8/24/20 11:27 AM, Catalin Marinas wrote:
> From: Vincenzo Frascino <vincenzo.frascino@arm.com>
> 
> Add Memory Tagging Extension support to the arm64 kbuild.
> 
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> ---
> 
> Notes:
>     v7:
>     - Binutils gained initial support for MTE in 2.32.0. However, a late
>       architecture addition (LDGM/STGM) is only supported in the newer
>       2.32.x and 2.33 versions. Change the AS_HAS_MTE option to also check
>       for stgm in addition to .arch armv8.5-a+memtag.
>     
>  arch/arm64/Kconfig | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6d232837cbee..10cf81d70657 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1664,6 +1664,37 @@ config ARCH_RANDOM
>  	  provides a high bandwidth, cryptographically secure
>  	  hardware random number generator.
>  
> +config ARM64_AS_HAS_MTE
> +	# Binutils gained initial support for MTE in 2.32.0. However, a
> +	# late architecture addition (LDGM/STGM) is only supported in
> +	# the newer 2.32.x and 2.33 versions.
> +	def_bool $(as-instr,.arch armv8.5-a+memtag\nstgm xzr$(comma)[x0])

Would you mind translating that for me?
Yes, I read the v7 Notes, but that only helped a little bit.


> +
> +config ARM64_MTE
> +	bool "Memory Tagging Extension support"
> +	default y
> +	depends on ARM64_AS_HAS_MTE && ARM64_TAGGED_ADDR_ABI
> +	select ARCH_USES_HIGH_VMA_FLAGS
> +	help
> +	  Memory Tagging (part of the ARMv8.5 Extensions) provides
> +	  architectural support for run-time, always-on detection of

	                            runtime,
as is used below.

> +	  various classes of memory error to aid with software debugging
> +	  to eliminate vulnerabilities arising from memory-unsafe
> +	  languages.
> +
> +	  This option enables the support for the Memory Tagging
> +	  Extension at EL0 (i.e. for userspace).
> +
> +	  Selecting this option allows the feature to be detected at
> +	  runtime. Any secondary CPU not implementing this feature will
> +	  not be allowed a late bring-up.
> +
> +	  Userspace binaries that want to use this feature must
> +	  explicitly opt in. The mechanism for the userspace is
> +	  described in:
> +
> +	  Documentation/arm64/memory-tagging-extension.rst.
> +
>  endmenu
>  
>  config ARM64_SVE
> 

thanks.
-- 
~Randy