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

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Message-ID: <2b7f73a9-4683-421e-b8f6-5835711cecf3@linux.ibm.com>
Date: Thu, 28 Aug 2025 12:44:50 -0700
From: Farhan Ali <alifm@...ux.ibm.com>
To: Matthew Rosato <mjrosato@...ux.ibm.com>, joro@...tes.org,
        schnelle@...ux.ibm.com
Cc: will@...nel.org, robin.murphy@....com, gerald.schaefer@...ux.ibm.com,
        jgg@...pe.ca, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, stable@...r.kernel.org,
        Cam Miller <cam@...ux.ibm.com>
Subject: Re: [PATCH] iommu/s390: Fix memory corruption when using identity
 domain

On 8/27/2025 2:08 PM, 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@...r.kernel.org
> Fixes: 64af12c6ec3a ("iommu/s390: implement iommu passthrough via identity domain")
> Reported-by: Cam Miller <cam@...ux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@...ux.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);
>
Reviewed-by: Farhan Ali <alifm@...ux.ibm.com>