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SubjectRe: [PATCH] RTIC: selinux: ARM64: Move selinux_state to a separate page
On 2021-02-17 02:02, Miguel Ojeda wrote:
> On Tue, Feb 16, 2021 at 11:22 AM Preeti Nagar <pnagar@codeaurora.org>
> wrote:
>>
>> The changes introduce a new security feature, RunTime Integrity Check
>> (RTIC), designed to protect Linux Kernel at runtime. The motivation
>> behind these changes is:
>> 1. The system protection offered by Security Enhancements(SE) for
>> Android relies on the assumption of kernel integrity. If the kernel
>> itself is compromised (by a perhaps as yet unknown future
>> vulnerability),
>> SE for Android security mechanisms could potentially be disabled and
>> rendered ineffective.
>> 2. Qualcomm Snapdragon devices use Secure Boot, which adds
>> cryptographic
>> checks to each stage of the boot-up process, to assert the
>> authenticity
>> of all secure software images that the device executes. However, due
>> to
>> various vulnerabilities in SW modules, the integrity of the system can
>> be
>> compromised at any time after device boot-up, leading to un-authorized
>> SW executing.
>>
>> The feature's idea is to move some sensitive kernel structures to a
>> separate page and monitor further any unauthorized changes to these,
>> from higher Exception Levels using stage 2 MMU. Moving these to a
>> different page will help avoid getting page faults from un-related
>> data.
>> The mechanism we have been working on removes the write permissions
>> for
>> HLOS in the stage 2 page tables for the regions to be monitored, such
>> that any modification attempts to these will lead to faults being
>> generated and handled by handlers. If the protected assets are moved
>> to
>> a separate page, faults will be generated corresponding to change
>> attempts
>> to these assets only. If not moved to a separate page, write attempts
>> to
>> un-related data present on the monitored pages will also be generated.
>>
>> Using this feature, some sensitive variables of the kernel which are
>> initialized after init or are updated rarely can also be protected
>> from
>> simple overwrites and attacks trying to modify these.
>>
>> Currently, the change moves selinux_state structure to a separate
>> page.
>> The page is 2MB aligned not 4K to avoid TLB related performance impact
>> as,
>> for some CPU core designs, the TLB does not cache 4K stage 2 (IPA to
>> PA)
>> mappings if the IPA comes from a stage 1 mapping. In future, we plan
>> to
>> move more security-related kernel assets to this page to enhance
>> protection.
>
> Part of this commit message should likely be added as a new file under
> Documentation/ somewhere.
>
Yes, that will be helpful, will put it in Documentation/security in the
next update. Thank you!

>> diff --git a/security/Kconfig b/security/Kconfig
>> index 7561f6f..1af913a 100644
>> --- a/security/Kconfig
>> +++ b/security/Kconfig
>> @@ -291,5 +291,16 @@ config LSM
>>
>> source "security/Kconfig.hardening"
>>
>> +config SECURITY_RTIC
>> + bool "RunTime Integrity Check feature"
>> + depends on ARM64
>> + help
>> + RTIC(RunTime Integrity Check) feature is to protect Linux
>> kernel
>> + at runtime. This relocates some of the security sensitive
>> kernel
>> + structures to a separate RTIC specific page.
>> +
>> + This is to enable monitoring and protection of these kernel
>> assets
>> + from a higher exception level(EL) against any unauthorized
>> changes.
>
> Rewording suggestion:
>
> The RTIC (RunTime Integrity Check) feature protects the kernel
> at runtime by relocating some of its security-sensitive
> structures
> to a separate RTIC-specific page. This enables monitoring and
> and protecting them from a higher exception level against
> unauthorized changes.
>
Thanks :)

> Cheers,
> Miguel

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