Re: [PATCH] tee: fix tee_ioctl_object_invoke_arg padding

[Arnd Bergmann]

On Fri, Dec 5, 2025, at 14:45, Harshal Dev wrote:
> On 12/4/2025 6:57 PM, Jens Wiklander wrote:
>> On Thu, Dec 4, 2025 at 11:17 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>> 
> The only user-space client which is currently using this ABI (as per 
> our knowledge)
> is the libqcomtee library: 
> https://github.com/quic/quic-teec/blob/main/libqcomtee/src/linux/tee.h#L432
>
> If I understand Arnd's concern correctly, if a compiler used to build 
> the user-space
> client skips the padding for tee_ioctl_object_invoke_arg, it could lead 
> to issues.
>
> Let's wait for Amir's view here as well, however I do think the 
> explicit padding would
> benefit here.
>

The problem is much narrower: as the amount of padding is determined
by the architecture specific ABI, kernel and userspace on the same
architecture always agree, and specifically 32-bit Arm userspace
and 64-bit Arm userspace (aarch64) also have the same rules, so there
is no problem on Qualcomm's platforms even with compat 32-bit userspace.

The only actual ABI problem would happen on 32-bit x86 (i386)
userspace running on a 64-bit x86 kernel, since i386-linux compilers
have different alignment rules from most other architectures.

        Arnd