Re: [PATCH v2 1/1] cdrom: Fix spectre-v1 gadget

[Phillip Potter <phil@philpotter.co.uk>]

On Mon, Jun 12, 2023 at 11:00:40AM +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 | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
> index 416f723a2dbb..ecf2b458c108 100644
> --- a/drivers/cdrom/cdrom.c
> +++ b/drivers/cdrom/cdrom.c
> @@ -264,6 +264,7 @@
>  #include <linux/errno.h>
>  #include <linux/kernel.h>
>  #include <linux/mm.h>
> +#include <linux/nospec.h>
>  #include <linux/slab.h> 
>  #include <linux/cdrom.h>
>  #include <linux/sysctl.h>
> @@ -2329,6 +2330,9 @@ static int cdrom_ioctl_media_changed(struct cdrom_device_info *cdi,
>  	if (arg >= cdi->capacity)
>  		return -EINVAL;
>  
> +	/* Prevent arg from speculatively bypassing the length check */
> +	barrier_nospec();
> +
>  	info = kmalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info)
>  		return -ENOMEM;
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 
Hi Jordy,

Thanks for the patch, I will review/build it properly tonight after
work, although at first glance it looks good to me. I'll be in touch.

Regards,
Phil Potter