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From:   Jordy Zomer <jordyzomer@google.com>
Date:   Mon, 12 Jun 2023 11:35:03 +0200
Message-ID: <CABjM8Zf_xSNirWzMFVi816CuZAdRT-9edOpX0j526fQXNUm7xg@mail.gmail.com>
Subject: Re: [PATCH 1/1] cdrom: Fix spectre-v1 gadget
To:     Phillip Potter <phil@philpotter.co.uk>
Cc:     linux-kernel@vger.kernel.org, pawan.kumar.gupta@linux.intel.com,
        linux-block@vger.kernel.org
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Thanks both! I assumed array_index_mask_nospec was the same as
array_index_nospec. I'll send a V2 your way soon :)


On Sat, Jun 10, 2023 at 9:10=E2=80=AFPM Phillip Potter <phil@philpotter.co.=
uk> wrote:
>
> On Fri, Jun 09, 2023 at 01:13:55PM +0000, Jordy Zomer wrote:
> > This patch fixes a spectre-v1 gadget in cdrom.
> > The gadget could be triggered by,
> >  speculatviely bypassing the cdi->capacity check.
> >
> > Signed-off-by: Jordy Zomer <jordyzomer@google.com>
> > ---
> >  drivers/cdrom/cdrom.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
> > index 416f723a2dbb..3c349bc0a269 100644
> > --- a/drivers/cdrom/cdrom.c
> > +++ b/drivers/cdrom/cdrom.c
> > @@ -233,6 +233,7 @@
> >
> >  ----------------------------------------------------------------------=
---*/
> >
> > +#include "asm/barrier.h"
> >  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> >
> >  #define REVISION "Revision: 3.20"
> > @@ -2329,6 +2330,8 @@ static int cdrom_ioctl_media_changed(struct cdrom=
_device_info *cdi,
> >       if (arg >=3D cdi->capacity)
> >               return -EINVAL;
> >
> > +     arg =3D array_index_mask_nospec(arg, cdi->capacity);
> > +
> >       info =3D kmalloc(sizeof(*info), GFP_KERNEL);
> >       if (!info)
> >               return -ENOMEM;
> > --
> > 2.41.0.162.gfafddb0af9-goog
> >
>
> Hi Jordy,
>
> Thanks for the patch, much appreciated. Sadly, as Pawan has already
> pointed out, array_index_mask_nospec actually changes the behaviour of
> this function, such that 'arg' would no longer be an array index.
>
> In addition, it seems to have triggered the kernel test robot with an
> alpha build error.
>
> Regards,
> Phil