linux-kernel - Re: [PATCH v7 10/11] virt: arm-cca-guest: TSM

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Message-ID: <6750c695194cd_2508129427@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 4 Dec 2024 13:16:05 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Steven Price <steven.price@....com>, <kvm@...r.kernel.org>,
	<kvmarm@...ts.linux.dev>
CC: Sami Mujawar <sami.mujawar@....com>, Catalin Marinas
	<catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>, Will Deacon
	<will@...nel.org>, James Morse <james.morse@....com>, Oliver Upton
	<oliver.upton@...ux.dev>, Suzuki K Poulose <suzuki.poulose@....com>, "Zenghui
 Yu" <yuzenghui@...wei.com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Joey Gouly <joey.gouly@....com>, "Alexandru
 Elisei" <alexandru.elisei@....com>, Christoffer Dall
	<christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
	<linux-coco@...ts.linux.dev>, Ganapatrao Kulkarni
	<gankulkarni@...amperecomputing.com>, Gavin Shan <gshan@...hat.com>, "Shanker
 Donthineni" <sdonthineni@...dia.com>, Alper Gun <alpergun@...gle.com>, "Dan
 Williams" <dan.j.williams@...el.com>, "Aneesh Kumar K . V"
	<aneesh.kumar@...nel.org>, Steven Price <steven.price@....com>
Subject: Re: [PATCH v7 10/11] virt: arm-cca-guest: TSM_REPORT support for
 realms

Steven Price wrote:
> From: Sami Mujawar <sami.mujawar@....com>
> 
> Introduce an arm-cca-guest driver that registers with
> the configfs-tsm module to provide user interfaces for
> retrieving an attestation token.
> 
> When a new report is requested the arm-cca-guest driver
> invokes the appropriate RSI interfaces to query an
> attestation token.
> 
> The steps to retrieve an attestation token are as follows:
>   1. Mount the configfs filesystem if not already mounted
>      mount -t configfs none /sys/kernel/config
>   2. Generate an attestation token
>      report=/sys/kernel/config/tsm/report/report0
>      mkdir $report
>      dd if=/dev/urandom bs=64 count=1 > $report/inblob
>      hexdump -C $report/outblob
>      rmdir $report
> 
> Signed-off-by: Sami Mujawar <sami.mujawar@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> Changes since v6:
>  * Avoid get_cpu() and instead make the init attestation call using
>    smp_call_function_single(). Improve comments to explain the logic.
>  * Minor code reorgnisation and comment cleanup following Gavin's review
>    (thanks!)
> ---
>  drivers/virt/coco/Kconfig                     |   2 +
>  drivers/virt/coco/Makefile                    |   1 +
>  drivers/virt/coco/arm-cca-guest/Kconfig       |  11 +
>  drivers/virt/coco/arm-cca-guest/Makefile      |   2 +
>  .../virt/coco/arm-cca-guest/arm-cca-guest.c   | 224 ++++++++++++++++++
>  5 files changed, 240 insertions(+)
>  create mode 100644 drivers/virt/coco/arm-cca-guest/Kconfig
>  create mode 100644 drivers/virt/coco/arm-cca-guest/Makefile
>  create mode 100644 drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
[..]
> diff --git a/drivers/virt/coco/arm-cca-guest/Kconfig b/drivers/virt/coco/arm-cca-guest/Kconfig
> new file mode 100644
> index 000000000000..9dd27c3ee215
> --- /dev/null
> +++ b/drivers/virt/coco/arm-cca-guest/Kconfig
> @@ -0,0 +1,11 @@
> +config ARM_CCA_GUEST
> +	tristate "Arm CCA Guest driver"
> +	depends on ARM64
> +	default m

I am working on some updates to the TSM_REPORTS interface, rebased them
to test the changes with this driver, and discovered that this driver is
enabled by default.

Just a reminder to please do not mark new drivers as "default m" [1]. In
this case it is difficult to imagine that every arm64 kernel on the
planet needs this functionality enabled by default. In general, someone
should be able to run olddefconfig with a new kernel and not be exposed
to brand new drivers that they have not considered previously.

[1]: http://lore.kernel.org/CA+55aFzxL6-Xp=-mnBwMisZsuKhRZ6zRDJoAmH8W5LDHU2oJuw@mail.gmail.com/