[PATCH v2] arm64: Add the arm64.no32bit_el0 command line option

[Will Deacon]

On Tue, Mar 05, 2024 at 11:56:05AM +0100, Andrea della Porta wrote:
> 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 at 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?

It looks reasonable to me, but arch/arm64/kernel/idreg-override.c no
longer exists upstream, so you need to rebase.

Thanks,

Will