Re: [PATCH] iommu/s390: Fix memory corruption when using identity domain

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2025-08-27 at 17:08 -0400, Matthew Rosato wrote:
> zpci_get_iommu_ctrs() returns counter information to be reported as part
> of device statistics; these counters are stored as part of the s390_domain.
> The problem, however, is that the identity domain is not backed by an
> s390_domain and so the conversion via to_s390_domain() yields a bad address
> that is zero'd initially and read on-demand later via a sysfs read.
> These counters aren't necessary for the identity domain; just return NULL
> in this case.
> 
> This issue was discovered via KASAN with reports that look like:
> BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device
> when using the identity domain for a device on s390.
> 
> Cc: stable@vger.kernel.org
> Fixes: 64af12c6ec3a ("iommu/s390: implement iommu passthrough via identity domain")
> Reported-by: Cam Miller <cam@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  drivers/iommu/s390-iommu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> index 9c80d61deb2c..d7370347c910 100644
> --- a/drivers/iommu/s390-iommu.c
> +++ b/drivers/iommu/s390-iommu.c
> @@ -1032,7 +1032,8 @@ struct zpci_iommu_ctrs *zpci_get_iommu_ctrs(struct zpci_dev *zdev)
>  
>  	lockdep_assert_held(&zdev->dom_lock);
>  
> -	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED)
> +	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED ||
> +	    zdev->s390_domain->type == IOMMU_DOMAIN_IDENTITY)
>  		return NULL;
>  
>  	s390_domain = to_s390_domain(zdev->s390_domain);

Looks good to me and thanks for the fix!

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>