lkml.org 
[lkml]   [2018]   [Dec]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/6] arm64: kpti: move check for non-vulnerable CPUs to a function
From
Date
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 */
>>
>

\
 
 \ /
  Last update: 2018-12-13 17:18    [W:0.087 / U:1.632 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site