[PATCH v12 19/39] arm64/mm: Handle GCS data aborts

[Catalin Marinas]

On Thu, Aug 29, 2024 at 12:27:35AM +0100, Mark Brown wrote:
> All GCS operations at EL0 must happen on a page which is marked as
> having UnprivGCS access, including read operations.  If a GCS operation
> attempts to access a page without this then it will generate a data
> abort with the GCS bit set in ESR_EL1.ISS2.
> 
> EL0 may validly generate such faults, for example due to copy on write
> which will cause the GCS data to be stored in a read only page with no
> GCS permissions until the actual copy happens.  Since UnprivGCS allows
> both reads and writes to the GCS (though only through GCS operations) we
> need to ensure that the memory management subsystem handles GCS accesses
> as writes at all times.  Do this by adding FAULT_FLAG_WRITE to any GCS
> page faults, adding handling to ensure that invalid cases are identfied
> as such early so the memory management core does not think they will
> succeed.  The core cannot distinguish between VMAs which are generally
> writeable and VMAs which are only writeable through GCS operations.
> 
> EL1 may validly write to EL0 GCS for management purposes (eg, while
> initialising with cap tokens).
> 
> We also report any GCS faults in VMAs not marked as part of a GCS as
> access violations, causing a fault to be delivered to userspace if it
> attempts to do GCS operations outside a GCS.
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann at linaro.org>
> Signed-off-by: Mark Brown <broonie at kernel.org>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>