Patchwork [1/6] arm64: kpti: move check for non-vulnerable CPUs to a function

login
register
mail settings
Submitter Jeremy Linton
Date Dec. 6, 2018, 11:44 p.m.
Message ID <20181206234408.1287689-2-jeremy.linton@arm.com>
Download mbox | patch
Permalink /patch/674843/
State New
Headers show

Comments

Jeremy Linton - Dec. 6, 2018, 11:44 p.m.
From: Mian Yousaf Kaukab <ykaukab@suse.de>

Add is_meltdown_safe() which is a whitelist of known safe cores.

Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
[Moved location of function]
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
---
 arch/arm64/kernel/cpufeature.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)
Jeremy Linton - Dec. 12, 2018, 2:36 p.m.
Hi Julien,

Thanks for looking at this,

On 12/13/2018 03:13 AM, Julien Thierry wrote:
> Hi,
> 
> On 06/12/2018 23:44, Jeremy Linton wrote:
>> From: Mian Yousaf Kaukab <ykaukab@suse.de>
>>
>> Add is_meltdown_safe() which is a whitelist of known safe cores.
>>
>> Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
>> [Moved location of function]
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   arch/arm64/kernel/cpufeature.c | 16 ++++++++++++----
>>   1 file changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index aec5ecb85737..242898395f68 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -908,8 +908,7 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
>>   #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>>   static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
>>   
>> -static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>> -				int scope)
>> +static bool is_cpu_meltdown_safe(void)
>>   {
>>   	/* List of CPUs that are not vulnerable and don't need KPTI */
>>   	static const struct midr_range kpti_safe_list[] = {
>> @@ -917,6 +916,16 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>>   		MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
>>   		{ /* sentinel */ }
>>   	};
>> +	/* Don't force KPTI for CPUs that are not vulnerable */
> 
> This is really a nit, but that comment would make more sense where
> is_cpu_meltdown_safe() is called since unmap_kernel_at_el0 is the one
> deciding whether to apply KPTI, is_cpu_meltdown_safe() just states
> whether the core is safe of not.

That is a good point, thanks.


> 
> Otherwise:
> 
> Reviewed-by: Julien Thierry <julien.thierry@arm.com>
> 
> Cheers,
> 
> Julien
> 
>> +	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> +static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>> +				int scope)
>> +{
>>   	char const *str = "command line option";
>>   
>>   	/*
>> @@ -940,8 +949,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>>   	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
>>   		return true;
>>   
>> -	/* Don't force KPTI for CPUs that are not vulnerable */
>> -	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
>> +	if (is_cpu_meltdown_safe())
>>   		return false;
>>   
>>   	/* Defer to CPU feature registers */
>>
>
Julien Thierry - Dec. 13, 2018, 9:13 a.m.
Hi,

On 06/12/2018 23:44, Jeremy Linton wrote:
> From: Mian Yousaf Kaukab <ykaukab@suse.de>
> 
> Add is_meltdown_safe() which is a whitelist of known safe cores.
> 
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
> [Moved location of function]
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  arch/arm64/kernel/cpufeature.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index aec5ecb85737..242898395f68 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -908,8 +908,7 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
>  #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>  static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
>  
> -static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> -				int scope)
> +static bool is_cpu_meltdown_safe(void)
>  {
>  	/* List of CPUs that are not vulnerable and don't need KPTI */
>  	static const struct midr_range kpti_safe_list[] = {
> @@ -917,6 +916,16 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>  		MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
>  		{ /* sentinel */ }
>  	};
> +	/* Don't force KPTI for CPUs that are not vulnerable */

This is really a nit, but that comment would make more sense where
is_cpu_meltdown_safe() is called since unmap_kernel_at_el0 is the one
deciding whether to apply KPTI, is_cpu_meltdown_safe() just states
whether the core is safe of not.

Otherwise:

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Cheers,

Julien

> +	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
> +		return true;
> +
> +	return false;
> +}
> +
> +static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> +				int scope)
> +{
>  	char const *str = "command line option";
>  
>  	/*
> @@ -940,8 +949,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>  	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
>  		return true;
>  
> -	/* Don't force KPTI for CPUs that are not vulnerable */
> -	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
> +	if (is_cpu_meltdown_safe())
>  		return false;
>  
>  	/* Defer to CPU feature registers */
>

Patch

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index aec5ecb85737..242898395f68 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -908,8 +908,7 @@  has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
 
-static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
-				int scope)
+static bool is_cpu_meltdown_safe(void)
 {
 	/* List of CPUs that are not vulnerable and don't need KPTI */
 	static const struct midr_range kpti_safe_list[] = {
@@ -917,6 +916,16 @@  static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 		MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
 		{ /* sentinel */ }
 	};
+	/* Don't force KPTI for CPUs that are not vulnerable */
+	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
+		return true;
+
+	return false;
+}
+
+static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
+				int scope)
+{
 	char const *str = "command line option";
 
 	/*
@@ -940,8 +949,7 @@  static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
 		return true;
 
-	/* Don't force KPTI for CPUs that are not vulnerable */
-	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
+	if (is_cpu_meltdown_safe())
 		return false;
 
 	/* Defer to CPU feature registers */