Re: [PATCH 0/3] arm64: cpufeature: Add filter function to control

[Marc Zyngier]

Hi Srinivas,

On 2021-01-09 00:29, Srinivas Ramana wrote:
> This patchset adds a control function for cpufeature framework
> so that the feature can be controlled at runtime.
>
> Defer PAC on boot core and use the filter function added to disable
> PAC from command line. This will help toggling the feature on systems
> that do not support PAC or where PAC needs to be disabled at runtime,
> without modifying the core kernel.
>
> The idea of adding the filter function for cpufeature is taken from
> https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-25-catalin.marinas@xxxxxxx/
> https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@xxxxxxx/
>
> Srinivas Ramana (3):
>   arm64: Defer enabling pointer authentication on boot core
>   arm64: cpufeature: Add a filter function to cpufeature
>   arm64: Enable control of pointer authentication using early param
>
>  Documentation/admin-guide/kernel-parameters.txt |  6 +++
>  arch/arm64/include/asm/cpufeature.h             |  8 +++-
>  arch/arm64/include/asm/pointer_auth.h           | 10 +++++
>  arch/arm64/include/asm/stackprotector.h         |  1 +
>  arch/arm64/kernel/cpufeature.c                  | 53 
> +++++++++++++++++++------
>  arch/arm64/kernel/head.S                        |  4 --
>  6 files changed, 64 insertions(+), 18 deletions(-)

I've been working for some time on a similar series to allow a feature
set to be disabled during the early boot phase, initially to prevent
booting a kernel with VHE, but the mechanism is generic enough to
deal with most architectural features.

I took the liberty to lift your first patch and to add it to my 
series[1],
further allowing PAuth to be disabled at boot time on top of BTI and 
VHE.

I'd appreciate your comments on this.

Thanks,

        M.

[1] https://lore.kernel.org/r/20210111132811.2455113-1-maz@xxxxxxxxxx
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