arm64: Add support for LPA2 at stage1 and WXN

[PATCH v3 30/60] arm64: idreg-override: Create a pseudo feature for rodata=off

Posted by Ard Biesheuvel 2 years, 9 months ago

Add rodata=off to the set of kernel command line options that is parsed
early using the CPU feature override detection code, so we can easily
refer to it when creating the kernel mapping.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h   | 1 +
 arch/arm64/kernel/pi/idreg-override.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index bc10098901808c00..edc7733aa49846b2 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -16,6 +16,7 @@
 #define cpu_feature(x)		KERNEL_HWCAP_ ## x
 
 #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR	0
+#define ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF	4
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index 4e76db6eb72c2087..6c547cccaf6a9e9c 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -151,6 +151,7 @@ static const struct ftr_set_desc sw_features __prel64_initconst = {
 	.override	= &arm64_sw_feature_override,
 	.fields		= {
 		FIELD("nokaslr", ARM64_SW_FEATURE_OVERRIDE_NOKASLR, NULL),
+		FIELD("rodataoff", ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF, NULL),
 		{}
 	},
 };
@@ -183,6 +184,7 @@ static const struct {
 	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
 	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
 	{ "nokaslr",			"arm64_sw.nokaslr=1" },
+	{ "rodata=off",			"arm64_sw.rodataoff=1" },
 };
 
 static int __init parse_hexdigit(const char *p, u64 *v)
-- 
2.39.2

Re: [PATCH v3 30/60] arm64: idreg-override: Create a pseudo feature for rodata=off

Posted by Ryan Roberts 2 years, 8 months ago

On 07/03/2023 14:04, Ard Biesheuvel wrote:
> Add rodata=off to the set of kernel command line options that is parsed
> early using the CPU feature override detection code, so we can easily
> refer to it when creating the kernel mapping.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/arm64/include/asm/cpufeature.h   | 1 +
>  arch/arm64/kernel/pi/idreg-override.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index bc10098901808c00..edc7733aa49846b2 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -16,6 +16,7 @@
>  #define cpu_feature(x)		KERNEL_HWCAP_ ## x
>  
>  #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR	0
> +#define ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF	4

I assume these are bit numbers? Why not just use the next available bit (bit 1)
for this new flag?

>  
>  #ifndef __ASSEMBLY__
>  
> diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
> index 4e76db6eb72c2087..6c547cccaf6a9e9c 100644
> --- a/arch/arm64/kernel/pi/idreg-override.c
> +++ b/arch/arm64/kernel/pi/idreg-override.c
> @@ -151,6 +151,7 @@ static const struct ftr_set_desc sw_features __prel64_initconst = {
>  	.override	= &arm64_sw_feature_override,
>  	.fields		= {
>  		FIELD("nokaslr", ARM64_SW_FEATURE_OVERRIDE_NOKASLR, NULL),
> +		FIELD("rodataoff", ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF, NULL),
>  		{}
>  	},
>  };
> @@ -183,6 +184,7 @@ static const struct {
>  	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
>  	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
>  	{ "nokaslr",			"arm64_sw.nokaslr=1" },
> +	{ "rodata=off",			"arm64_sw.rodataoff=1" },
>  };
>  
>  static int __init parse_hexdigit(const char *p, u64 *v)

Re: [PATCH v3 30/60] arm64: idreg-override: Create a pseudo feature for rodata=off

Posted by Ard Biesheuvel 2 years, 8 months ago

On Mon, 17 Apr 2023 at 16:28, Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 07/03/2023 14:04, Ard Biesheuvel wrote:
> > Add rodata=off to the set of kernel command line options that is parsed
> > early using the CPU feature override detection code, so we can easily
> > refer to it when creating the kernel mapping.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  arch/arm64/include/asm/cpufeature.h   | 1 +
> >  arch/arm64/kernel/pi/idreg-override.c | 2 ++
> >  2 files changed, 3 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> > index bc10098901808c00..edc7733aa49846b2 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -16,6 +16,7 @@
> >  #define cpu_feature(x)               KERNEL_HWCAP_ ## x
> >
> >  #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR    0
> > +#define ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF 4
>
> I assume these are bit numbers? Why not just use the next available bit (bit 1)
> for this new flag?
>

This (ab)uses the CPU feature framework, which is based on 4-bit
quantities. I don't remember if it matters or not, but IIRC the
default macros use 4-bit wide values.

Re: [PATCH v3 30/60] arm64: idreg-override: Create a pseudo feature for rodata=off

Posted by Ryan Roberts 2 years, 8 months ago

On 17/04/2023 15:30, Ard Biesheuvel wrote:
> On Mon, 17 Apr 2023 at 16:28, Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> On 07/03/2023 14:04, Ard Biesheuvel wrote:
>>> Add rodata=off to the set of kernel command line options that is parsed
>>> early using the CPU feature override detection code, so we can easily
>>> refer to it when creating the kernel mapping.
>>>
>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>> ---
>>>  arch/arm64/include/asm/cpufeature.h   | 1 +
>>>  arch/arm64/kernel/pi/idreg-override.c | 2 ++
>>>  2 files changed, 3 insertions(+)
>>>
>>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>>> index bc10098901808c00..edc7733aa49846b2 100644
>>> --- a/arch/arm64/include/asm/cpufeature.h
>>> +++ b/arch/arm64/include/asm/cpufeature.h
>>> @@ -16,6 +16,7 @@
>>>  #define cpu_feature(x)               KERNEL_HWCAP_ ## x
>>>
>>>  #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR    0
>>> +#define ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF 4
>>
>> I assume these are bit numbers? Why not just use the next available bit (bit 1)
>> for this new flag?
>>
> 
> This (ab)uses the CPU feature framework, which is based on 4-bit
> quantities. I don't remember if it matters or not, but IIRC the
> default macros use 4-bit wide values.

OK, thanks.