linux-kernel - Re: [PATCH v10 3/4] random: introduce generic vDSO getrandom() implementation

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Message-ID: <Y4dt1dLZMmogRlKa@zx2c4.com>
Date:   Wed, 30 Nov 2022 15:51:01 +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,
        linux-api@...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>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v10 3/4] random: introduce generic vDSO getrandom()
 implementation

Hi Florian,

On Wed, Nov 30, 2022 at 11:44:30AM +0100, Florian Weimer wrote:
> * Jason A. Donenfeld:
> 
> > diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
> > index 73eb622e7663..9ae4d76b36c7 100644
> > --- a/include/vdso/datapage.h
> > +++ b/include/vdso/datapage.h
> > @@ -109,6 +109,16 @@ struct vdso_data {
> >  	struct arch_vdso_data	arch_data;
> >  };
> >  
> > +/**
> > + * struct vdso_rng_data - vdso RNG state information
> > + * @generation:	a counter representing the number of RNG reseeds
> > + * @is_ready:	whether the RNG is initialized
> > + */
> > +struct vdso_rng_data {
> > +	unsigned long	generation;
> > +	bool		is_ready;
> > +};
> > +
> 
> I don't think you can use a type like long here.  The header says this:
> 
>  * vdso_data will be accessed by 64 bit and compat code at the same time
>  * so we should be careful before modifying this structure.
> 
> So the ABI must be same for 32-bit and 64-bit mode, and long isn't.

Excellent point. The size of the type needs to be explicit. Will fix.

Jason