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Date: Tue, 5 Mar 2024 11:56:05 +0100
From: Andrea della Porta <aporta@suse.de>
To: Andrea della Porta <andrea.porta@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64: Add the arm64.no32bit_el0 command line option
Message-ID: <Zeb6RX2wpBvuJiIZ@apocalypse>
Mail-Followup-To: Andrea della Porta <andrea.porta@suse.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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In-Reply-To: <20240207105847.7739-1-andrea.porta@suse.com>

On 11:58 Wed 07 Feb     , Andrea della Porta wrote:
> Introducing the field 'el0' to the idreg-override for register
> ID_AA64PFR0_EL1. This field is also aliased to the new kernel
> command line option 'arm64.no32bit_el0' as a more recognizable
> and mnemonic name to disable the execution of 32 bit userspace
> applications (i.e. avoid Aarch32 execution state in EL0) from
> kernel command line.
> 
> Changes in V2:
> - fixed the order of appearance of arm64.no32bit_el0 entry in
>   kernel-parameters.txt documentation.
> 
> Link: https://lore.kernel.org/r/ZVTleETzfFUchs77@apocalypse
> Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  arch/arm64/kernel/idreg-override.c              | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 65731b060e3f..fa7cdf2f4f3a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -415,6 +415,9 @@
>  	arcrimi=	[HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
>  			Format: <io>,<irq>,<nodeID>
>  
> +	arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of
> +			32 bit applications
> +
>  	arm64.nobti	[ARM64] Unconditionally disable Branch Target
>  			Identification support
>  
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index e30fd9e32ef3..642cda19e42d 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -86,6 +86,7 @@ static const struct ftr_set_desc pfr0 __prel64_initconst = {
>  	.override	= &id_aa64pfr0_override,
>  	.fields		= {
>  	        FIELD("sve", ID_AA64PFR0_EL1_SVE_SHIFT, pfr0_sve_filter),
> +		FIELD("el0", ID_AA64PFR0_EL1_EL0_SHIFT, NULL),
>  		{}
>  	},
>  };
> @@ -197,6 +198,7 @@ static const struct {
>  	{ "arm64.nomops",		"id_aa64isar2.mops=0" },
>  	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
>  	{ "nokaslr",			"arm64_sw.nokaslr=1" },
> +	{ "arm64.no32bit_el0",		"id_aa64pfr0.el0=1" },
>  };
>  
>  static int __init parse_hexdigit(const char *p, u64 *v)
> -- 
> 2.41.0
> 

A gentle ping about this patch... any thoughts about it?

Many thanks,
Andrea