On 21.04.21 14:58, Greg Kroah-Hartman wrote:
> This reverts commit d6bd6cf9feb81737f9f64d2c1acf98fdaacebad1.
> 
> Commits from @umn.edu addresses have been found to be submitted in "bad
> faith" to try to test the kernel community's ability to review "known
> malicious" changes.  The result of these submissions can be found in a
> paper published at the 42nd IEEE Symposium on Security and Privacy
> entitled, "Open Source Insecurity: Stealthily Introducing
> Vulnerabilities via Hypocrite Commits" written by Qiushi Wu (University
> of Minnesota) and Kangjie Lu (University of Minnesota).
> 
> Because of this, all submissions from this group must be reverted from
> the kernel tree and will need to be re-reviewed again to determine if
> they actually are a valid fix.  Until that work is complete, remove this
> change to ensure that no problems are being introduced into the
> codebase.
> 
> Cc: Aditya Pakki <pakki001@umn.edu>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Juergen Gross <jgross@suse.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The reverted patch didn't introduce any issue. I have verified that the
BUG_ON()s are really impossible to trigger, and even if they would have
been triggering, they'd be now replaced by NULL dereferences.

So I believe you can just drop this revert.


Juergen

> ---
>   drivers/xen/grant-table.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 3729bea0c989..5065d36c602e 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -663,6 +663,7 @@ static int grow_gnttab_list(unsigned int more_frames)
>   	unsigned int nr_glist_frames, new_nr_glist_frames;
>   	unsigned int grefs_per_frame;
>   
> +	BUG_ON(gnttab_interface == NULL);
>   	grefs_per_frame = gnttab_interface->grefs_per_grant_frame;
>   
>   	new_nr_grant_frames = nr_grant_frames + more_frames;
> @@ -1281,6 +1282,7 @@ EXPORT_SYMBOL_GPL(gnttab_unmap_refs_sync);
>   
>   static unsigned int nr_status_frames(unsigned int nr_grant_frames)
>   {
> +	BUG_ON(gnttab_interface == NULL);
>   	return gnttab_frames(nr_grant_frames, SPP);
>   }
>   
> @@ -1508,6 +1510,7 @@ static int gnttab_expand(unsigned int req_entries)
>   	int rc;
>   	unsigned int cur, extra;
>   
> +	BUG_ON(gnttab_interface == NULL);
>   	cur = nr_grant_frames;
>   	extra = ((req_entries + gnttab_interface->grefs_per_grant_frame - 1) /
>   		 gnttab_interface->grefs_per_grant_frame);
> @@ -1542,6 +1545,7 @@ int gnttab_init(void)
>   	/* Determine the maximum number of frames required for the
>   	 * grant reference free list on the current hypervisor.
>   	 */
> +	BUG_ON(gnttab_interface == NULL);
>   	max_nr_glist_frames = (max_nr_grant_frames *
>   			       gnttab_interface->grefs_per_grant_frame / RPP);
>   
>