linux-kernel - Re: [PATCH] habanalabs: fix potential spectre v1 gadgets

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Date:   Wed, 2 Feb 2022 12:22:29 +0200
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Jordy Zomer <jordy@...ing.systems>
Cc:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ofir Bitton <obitton@...ana.ai>,
        Dani Liberman <dliberman@...ana.ai>,
        Tomer Tayar <ttayar@...ana.ai>, Koby Elbaz <kelbaz@...ana.ai>,
        farah kassabri <fkassabri@...ana.ai>,
        Sagiv Ozeri <sozeri@...ana.ai>,
        Yuri Nudelman <ynudelman@...ana.ai>
Subject: Re: [PATCH] habanalabs: fix potential spectre v1 gadgets

On Wed, Feb 2, 2022 at 9:50 AM Oded Gabbay <ogabbay@...nel.org> wrote:
>
> On Tue, Feb 1, 2022 at 7:25 PM Jordy Zomer <jordy@...ing.systems> wrote:
> >
> > It appears like nr could be a Spectre v1 gadget as it's supplied by a
> > user and used as an array index. Prevent the contents
> > of kernel memory from being leaked to userspace via speculative
> > execution by using array_index_nospec.
> >
> > Signed-off-by: Jordy Zomer <jordy@...ing.systems>
> > ---
> >  drivers/misc/habanalabs/common/habanalabs_ioctl.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/misc/habanalabs/common/habanalabs_ioctl.c b/drivers/misc/habanalabs/common/habanalabs_ioctl.c
> > index 3ba3a8ffda3e..c1cdf712a10d 100644
> > --- a/drivers/misc/habanalabs/common/habanalabs_ioctl.c
> > +++ b/drivers/misc/habanalabs/common/habanalabs_ioctl.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/fs.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/slab.h>
> > +#include <linux/nospec.h>
> >
> >  static u32 hl_debug_struct_size[HL_DEBUG_OP_TIMESTAMP + 1] = {
> >         [HL_DEBUG_OP_ETR] = sizeof(struct hl_debug_params_etr),
> > @@ -849,6 +850,7 @@ long hl_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> >         }
> >
> >         if ((nr >= HL_COMMAND_START) && (nr < HL_COMMAND_END)) {
> > +               nr = array_index_nospec(nr, HL_COMMAND_END-1);
This needs to be HL_COMMAND_END.
The pattern (as described in array_index_nospec comment) is
if (index < size) {
        index = array_index_nospec(index, size);
        val = array[index];
}

When you do -1, it misses the last value which causes that ioctl to
get rejected.

> >                 ioctl = &hl_ioctls[nr];
> >         } else {
> >                 dev_err(hdev->dev, "invalid ioctl: pid=%d, nr=0x%02x\n",
> > @@ -872,6 +874,7 @@ long hl_ioctl_control(struct file *filep, unsigned int cmd, unsigned long arg)
> >         }
> >
> >         if (nr == _IOC_NR(HL_IOCTL_INFO)) {
> > +               nr = array_index_nospec(nr, _IOC_NR(HL_IOCTL_INFO));
same here, it should be _IOC_NR(HL_IOCTL_INFO) + 1

Thanks,
Oded

> >                 ioctl = &hl_ioctls_control[nr];
> >         } else {
> >                 dev_err(hdev->dev_ctrl, "invalid ioctl: pid=%d, nr=0x%02x\n",
> > --
> > 2.27.0
> >
>
> Thanks for the patch.
> I'm going to run this through our CI and if nothing breaks I'll merge
> it to our -next branch.
>
> Oded