Re: [PATCH v3 03/17] arm64: Turn kaslr_feature_override into a generic SW feature override

[Shaoqin Huang <shahuang@xxxxxxxxxx>]

On 6/10/23 00:21, Marc Zyngier wrote:
> Disabling KASLR from the command line is implemented as a feature
> override. Repaint it slightly so that it can further be used as
> more generic infrastructure for SW override purposes.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
> ---
>   arch/arm64/include/asm/cpufeature.h |  4 ++++
>   arch/arm64/kernel/cpufeature.c      |  2 ++
>   arch/arm64/kernel/idreg-override.c  | 16 ++++++----------
>   arch/arm64/kernel/kaslr.c           |  6 +++---
>   4 files changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 6bf013fb110d..bc1009890180 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -15,6 +15,8 @@
>   #define MAX_CPU_FEATURES	128
>   #define cpu_feature(x)		KERNEL_HWCAP_ ## x
>   
> +#define ARM64_SW_FEATURE_OVERRIDE_NOKASLR	0
> +
>   #ifndef __ASSEMBLY__
>   
>   #include <linux/bug.h>
> @@ -925,6 +927,8 @@ extern struct arm64_ftr_override id_aa64smfr0_override;
>   extern struct arm64_ftr_override id_aa64isar1_override;
>   extern struct arm64_ftr_override id_aa64isar2_override;
>   
> +extern struct arm64_ftr_override arm64_sw_feature_override;
> +
>   u32 get_kvm_ipa_limit(void);
>   void dump_cpu_features(void);
>   
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 7d7128c65161..2d2b7bb5fa0c 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -664,6 +664,8 @@ struct arm64_ftr_override __ro_after_init id_aa64smfr0_override;
>   struct arm64_ftr_override __ro_after_init id_aa64isar1_override;
>   struct arm64_ftr_override __ro_after_init id_aa64isar2_override;
>   
> +struct arm64_ftr_override arm64_sw_feature_override;
> +
>   static const struct __ftr_reg_entry {
>   	u32			sys_id;
>   	struct arm64_ftr_reg 	*reg;
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index 370ab84fd06e..8c93b6198bf5 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -138,15 +138,11 @@ static const struct ftr_set_desc smfr0 __initconst = {
>   	},
>   };
>   
> -extern struct arm64_ftr_override kaslr_feature_override;
> -
> -static const struct ftr_set_desc kaslr __initconst = {
> -	.name		= "kaslr",
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	.override	= &kaslr_feature_override,
> -#endif
> +static const struct ftr_set_desc sw_features __initconst = {
> +	.name		= "arm64_sw",
> +	.override	= &arm64_sw_feature_override,
>   	.fields		= {
> -		FIELD("disabled", 0, NULL),
> +		FIELD("nokaslr", ARM64_SW_FEATURE_OVERRIDE_NOKASLR, NULL),
>   		{}
>   	},
>   };
> @@ -158,7 +154,7 @@ static const struct ftr_set_desc * const regs[] __initconst = {
>   	&isar1,
>   	&isar2,
>   	&smfr0,
> -	&kaslr,
> +	&sw_features,
>   };
>   
>   static const struct {
> @@ -175,7 +171,7 @@ static const struct {
>   	  "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
>   	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
>   	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
> -	{ "nokaslr",			"kaslr.disabled=1" },
> +	{ "nokaslr",			"arm64_sw.nokaslr=1" },
>   };
>   
>   static int __init parse_nokaslr(char *unused)
> diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
> index e7477f21a4c9..5d4ce7f5f157 100644
> --- a/arch/arm64/kernel/kaslr.c
> +++ b/arch/arm64/kernel/kaslr.c
> @@ -23,8 +23,6 @@
>   u64 __ro_after_init module_alloc_base;
>   u16 __initdata memstart_offset_seed;
>   
> -struct arm64_ftr_override kaslr_feature_override __initdata;
> -
>   static int __init kaslr_init(void)
>   {
>   	u64 module_range;
> @@ -36,7 +34,9 @@ static int __init kaslr_init(void)
>   	 */
>   	module_alloc_base = (u64)_etext - MODULES_VSIZE;
>   
> -	if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
> +	if (cpuid_feature_extract_unsigned_field(arm64_sw_feature_override.val &
> +						 arm64_sw_feature_override.mask,
> +						 ARM64_SW_FEATURE_OVERRIDE_NOKASLR)) {
>   		pr_info("KASLR disabled on command line\n");
>   		return 0;
>   	}

--
Shaoqin