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@pwning.systems>
---
 drivers/dma-buf/dma-heap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index 56bf5ad01ad5..8f5848aa144f 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -14,6 +14,7 @@
 #include <linux/xarray.h>
 #include <linux/list.h>
 #include <linux/slab.h>
+#include <linux/nospec.h>
 #include <linux/uaccess.h>
 #include <linux/syscalls.h>
 #include <linux/dma-heap.h>
@@ -135,6 +136,7 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd,
 	if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
 		return -EINVAL;
 
+	nr = array_index_nospec(nr, ARRAY_SIZE(dma_heap_ioctl_cmds));
 	/* Get the kernel ioctl cmd that matches */
 	kcmd = dma_heap_ioctl_cmds[nr];
 
-- 
2.27.0

On Sat, Jan 29, 2022 at 7:06 AM Jordy Zomer <jordy@pwning.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@pwning.systems>
> ---
>  drivers/dma-buf/dma-heap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 56bf5ad01ad5..8f5848aa144f 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -14,6 +14,7 @@
>  #include <linux/xarray.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
> +#include <linux/nospec.h>
>  #include <linux/uaccess.h>
>  #include <linux/syscalls.h>
>  #include <linux/dma-heap.h>
> @@ -135,6 +136,7 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd,
>         if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
>                 return -EINVAL;
>
> +       nr = array_index_nospec(nr, ARRAY_SIZE(dma_heap_ioctl_cmds));
>         /* Get the kernel ioctl cmd that matches */
>         kcmd = dma_heap_ioctl_cmds[nr];

Thanks for submitting this! It looks sane to me.

Acked-by: John Stultz <john.stultz@linaro.org>

thanks
-john

Hello Jordy,

On Tue, 1 Feb 2022 at 02:09, John Stultz <john.stultz@linaro.org> wrote:
>
> On Sat, Jan 29, 2022 at 7:06 AM Jordy Zomer <jordy@pwning.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@pwning.systems>
Thanks very much for your patch; I've pushed it to drm-misc-fixes, so
we should see it in mainline soon.

> > ---
> >  drivers/dma-buf/dma-heap.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> > index 56bf5ad01ad5..8f5848aa144f 100644
> > --- a/drivers/dma-buf/dma-heap.c
> > +++ b/drivers/dma-buf/dma-heap.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/xarray.h>
> >  #include <linux/list.h>
> >  #include <linux/slab.h>
> > +#include <linux/nospec.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/syscalls.h>
> >  #include <linux/dma-heap.h>
> > @@ -135,6 +136,7 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd,
> >         if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
> >                 return -EINVAL;
> >
> > +       nr = array_index_nospec(nr, ARRAY_SIZE(dma_heap_ioctl_cmds));
> >         /* Get the kernel ioctl cmd that matches */
> >         kcmd = dma_heap_ioctl_cmds[nr];
>
> Thanks for submitting this! It looks sane to me.
>
> Acked-by: John Stultz <john.stultz@linaro.org>
>
> thanks
> -john


Best,
Sumit.