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

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Message-ID: <20230609234619.3bkmlgpxzaetua4d@desk>
Date:   Fri, 9 Jun 2023 16:46:19 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Jordy Zomer <jordyzomer@...gle.com>
Cc:     linux-kernel@...r.kernel.org, phil@...lpotter.co.uk
Subject: Re: [PATCH 1/1] cdrom: Fix spectre-v1 gadget

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@...gle.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 >= cdi->capacity)
>  		return -EINVAL;
>  
> +	arg = array_index_mask_nospec(arg, cdi->capacity);

array_index_nospec() is the correct function to use. The above generates
a mask and not the original value. Also it is effective when the second
argument is a build time constant. If thats not possible and this
function is not called very often barrier_nospec() is also an option.