Re: [PATCH v2] drivers/crypto: Mark QCE as BROKEN

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 7/13/26 11:31, Greg KH wrote:
> On Mon, Jul 13, 2026 at 10:42:04AM -0400, Demi Marie Obenour wrote:
>> On 7/13/26 09:07, Eric Biggers wrote:
>>> On Mon, Jul 13, 2026 at 06:47:07AM +0200, Greg KH wrote:
>>>> On Sun, Jul 12, 2026 at 05:31:31PM -0400, Demi Marie Obenour via B4 Relay wrote:
>>>>> From: Demi Marie Obenour <demiobenour@gmail.com>
>>>>>
>>>>> This driver is harmful:
>>>>>
>>>>> - It is much slower than the CPU [1] [2].
>>>>> - It Has a history of bugs [2] [3].
>>>>> - It does not have exclusive access to the hardware [4], causing races
>>>>>   with the secure world.
>>>>> - It register its implementations with too low a cra_priority for them
>>>>>   to be actually used [5].
>>>>>
>>>>> Therefore, disable it to ensure that nobody builds it into kernels they
>>>>> intend to ship.
>>>>>
>>>>> In the future, the driver will be used for processing restricted media
>>>>> content.  However, the kernel does not currently support this.  Since
>>>>> the driver will have future uses, allow building it if COMPILE_TEST is
>>>>> enabled.
>>>>
>>>> Why not just delete it now, and then bring it back when it is needed in
>>>> the future?  Otherwise this will just trip up the static code checkers
>>>> who will attempt to "fix" things in it.
>>>
>>> That makes sense to me, but Qualcomm pushed back on deletion:
>>> https://lore.kernel.org/linux-crypto/20260602-qcom-qce-broken-v1-1-a4ef756089e0@oss.qualcomm.com/
>>>
>>> But I've still not seen any evidence that this driver is useful for
>>> anything or has any users.  Even Qualcomm seems to be unwilling to make
>>> such claims; they only claim that the IP is used (i.e., not in Linux)
>>> and that new features are planned.
>>>
>>> - Eric
>>
>> Here is my reading of Qualcomm's statements:
>>
>> QCE is currently used by the Arm secure world.  In the future, QCE
>> will be used by the kernel as part of restricted content playback.
>> Qualcomm wants to add the needed features to the existing driver.
>> This will not use the crypto API.
> 
> Why is a crypto driver not going to use the crypto API?

I suspect that the restricted content playback use-case involves
QCE decrypting data stored in kernel memory, using keys inaccessible
to the kernel, to memory inaccessible to the kernel.  The crypto API
can't express this.

>> I would be fine with the driver being removed, but not if it means
>> another out-of-tree Android driver.
> 
> It's not another out-of-tree Android driver if nothing in Android
> actually uses it :)

Nothing uses it *yet*.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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