Re: [PATCH] iommu: fix crash in report_iommu_fault()

[Jason Gunthorpe]

On Wed, Apr 09, 2025 at 12:33:41AM +0300, Fedor Pchelkin wrote:
> The following crash is observed while handling an IOMMU fault with a
> recent kernel:
> 
> kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
> BUG: unable to handle page fault for address: ffff8c708299f700
> PGD 19ee01067 P4D 19ee01067 PUD 101c10063 PMD 80000001028001e3
> Oops: Oops: 0011 [#1] SMP NOPTI
> CPU: 4 UID: 0 PID: 139 Comm: irq/25-AMD-Vi Not tainted 6.15.0-rc1+ #20 PREEMPT(lazy)
> Hardware name: LENOVO 21D0/LNVNB161216, BIOS J6CN50WW 09/27/2024
> RIP: 0010:0xffff8c708299f700
> Call Trace:
>  <TASK>
>  ? report_iommu_fault+0x78/0xd3
>  ? amd_iommu_report_page_fault+0x91/0x150
>  ? amd_iommu_int_thread+0x77/0x180
>  ? __pfx_irq_thread_fn+0x10/0x10
>  ? irq_thread_fn+0x23/0x60
>  ? irq_thread+0xf9/0x1e0
>  ? __pfx_irq_thread_dtor+0x10/0x10
>  ? __pfx_irq_thread+0x10/0x10
>  ? kthread+0xfc/0x240
>  ? __pfx_kthread+0x10/0x10
>  ? ret_from_fork+0x34/0x50
>  ? __pfx_kthread+0x10/0x10
>  ? ret_from_fork_asm+0x1a/0x30
>  </TASK>
> 
> report_iommu_fault() checks for an installed handler comparing the
> corresponding field to NULL. It can (and could before) be called for a
> domain with a different cookie type - IOMMU_COOKIE_DMA_IOVA, specifically.
> Cookie is represented as a union so we may end up with a garbage value
> treated there if this happens for a domain with another cookie type.
> 
> Formerly there were two exclusive cookie types in the union.
> IOMMU_DOMAIN_SVA has a dedicated iommu_report_device_fault().
> 
> Call the fault handler only if the passed domain has a required cookie
> type.
> 
> Found by Linux Verification Center (linuxtesting.org).
> 
> Fixes: 6aa63a4ec947 ("iommu: Sort out domain user data")
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
> ---

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

This should go to rc

> > iommu-dma itself isn't ever going to use a fault 
> > handler because it expects the DMA API to be used correctly and thus no 
> > faults to occur.
> 
> My first thought about this is that iommu-dma is not interested in
> installing a fault handler ever, okay. But why does it suppose that no
> faults would occur? It is a matter of "chance", firmware bugs, abovesaid
> DMA API abusing, etc... isn't it?

Yes, it should not happen, this driver is clearly buggy.

Jason