linux-kernel - Re: [PATCH v6 1/3] random: add vgetrandom

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Message-ID: <Y37DDX5RtiGsV6MO@zx2c4.com>
Date:   Thu, 24 Nov 2022 02:04:13 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        tglx@...utronix.de, linux-crypto@...r.kernel.org, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
        Carlos O'Donell <carlos@...hat.com>
Subject: Re: [PATCH v6 1/3] random: add vgetrandom_alloc() syscall

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.

Jason