Diffstat (limited to 'drivers/firmware/efi/Kconfig')
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index bcc378c19ebe..ecc83e2f032c 100644
@@ -215,6 +215,28 @@ config EFI_RCI2_TABLE
Say Y here for Dell EMC PowerEdge systems.
+ bool "Clear Busmaster bit on PCI bridges during ExitBootServices()"
+ Disable the busmaster bit in the control register on all PCI bridges
+ while calling ExitBootServices() and passing control to the runtime
+ kernel. System firmware may configure the IOMMU to prevent malicious
+ PCI devices from being able to attack the OS via DMA. However, since
+ firmware can't guarantee that the OS is IOMMU-aware, it will tear
+ down IOMMU configuration when ExitBootServices() is called. This
+ leaves a window between where a hostile device could still cause
+ damage before Linux configures the IOMMU again.
+ If you say Y here, the EFI stub will clear the busmaster bit on all
+ PCI bridges before ExitBootServices() is called. This will prevent
+ any malicious PCI devices from being able to perform DMA until the
+ kernel reenables busmastering after configuring the IOMMU.
+ This option will cause failures with some poorly behaved hardware
+ and should not be enabled without testing. The kernel commandline
+ options "efi=disable_early_pci_dma" or "efi=no_disable_early_pci_dma"
+ may be used to override this option.