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From:   Florian Weimer <fweimer@redhat.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-kernel@vger.kernel.org, patches@lists.linux.dev,
        tglx@linutronix.de, linux-crypto@vger.kernel.org, x86@kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
        Carlos O'Donell <carlos@redhat.com>
Subject: Re: [PATCH v6 1/3] random: add vgetrandom_alloc() syscall
References: <20221121152909.3414096-1-Jason@zx2c4.com>
        <20221121152909.3414096-2-Jason@zx2c4.com>
        <87v8n6lzh9.fsf@oldenburg.str.redhat.com> <Y37DDX5RtiGsV6MO@zx2c4.com>
        <87a64g7wks.fsf@oldenburg.str.redhat.com> <Y39djiBSmgXfgWJv@zx2c4.com>
Date:   Thu, 24 Nov 2022 13:15:24 +0100
In-Reply-To: <Y39djiBSmgXfgWJv@zx2c4.com> (Jason A. Donenfeld's message of
        "Thu, 24 Nov 2022 13:03:26 +0100")
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* Jason A. Donenfeld:

> Hi Florian,
>
> On Thu, Nov 24, 2022 at 06:25:39AM +0100, Florian Weimer wrote:
>> * Jason A. Donenfeld:
>> 
>> > Hi Florian,
>> >
>> > On Wed, Nov 23, 2022 at 11:46:58AM +0100, Florian Weimer wrote:
>> >> * Jason A. Donenfeld:
>> >> 
>> >> > + * The vgetrandom() function in userspace requires an opaque state, which this
>> >> > + * function provides to userspace, by mapping a certain number of special pages
>> >> > + * into the calling process. It takes a hint as to the number of opaque states
>> >> > + * desired, and returns the number of opaque states actually allocated, the
>> >> > + * size of each one in bytes, and the address of the first state.
>> >> > + */
>> >> > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned long __user *, num,
>> >> > +		unsigned long __user *, size_per_each, unsigned int, flags)
>> >> 
>> >> I think you should make this __u64, so that you get a consistent
>> >> userspace interface on all architectures, without the need for compat
>> >> system calls.
>> >
>> > That would be quite unconventional. Most syscalls that take lengths do
>> > so with the native register size (`unsigned long`, `size_t`), rather
>> > than u64. If you can point to a recent trend away from this by
>> > indicating some commits that added new syscalls with u64, I'd be happy
>> > to be shown otherwise. But AFAIK, that's not the way it's done.
>> 
>> See clone3 and struct clone_args.
>
> The struct is one thing. But actually, clone3 takes a `size_t`:
>
>     SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size)
>
> I take from this that I too should use `size_t` rather than `unsigned
> long.` And it doesn't seem like there's any compat clone3.

But vgetrandom_alloc does not use unsigned long, but unsigned long *.
You need to look at the contents for struct clone_args for comparison.

Thanks,
Florian