Faulty, vulnerable or malicious PCIe devices can harm a system through DMA.
IOMMUs can act as a security mechanism to protect against
this problem by restricting the memory that is accessible via DMA.

Unfortunately, there are methods to bypass the IOMMU restrictions.
This paper is a survey over the currently existing bypasses and their feasibility.
Current systems might be exploited from any untrusted source of DMA, which includes
peripheral PCIe devices, virtual machines using SR-IOV, and even RDMA network
cards, which enable remote attacks. Key strategies for the attacks presented here
are Rowhammer, cache side-channels, and the exploitation
of weaknesses in device drivers, e.g., for network cards,
or protocols like PCIe or Ethernet OAM.
An attacker can potentially achieve denial of service,
the reading of confidential data, and even arbitrary code execution.
Fortunately, there are some precautions to reduce the risks for affected systems.