tree 25cb9728e28f1bcbf8d80483ab5eb0a0e4015b78
parent 84998f21b3c758233e7d8b3d1681d69f9d65ce14
author Alexandru Elisei <alexandru.elisei@arm.com> 1586875180 +0100
committer Will Deacon <will@kernel.org> 1586964437 +0100

vfio/pci: Ignore expansion ROM BAR writes

To get the size of the expansion ROM, software writes 0xfffff800 to the
expansion ROM BAR in the PCI configuration space. PCI emulation executes
the optional configuration space write callback that a device can implement
before emulating this write.

kvmtool's implementation of VFIO doesn't have support for emulating
expansion ROMs. However, the callback writes the guest value to the
hardware BAR, and then it reads it back to the emulated BAR to make sure
the write has completed successfully.

After this, we return to regular PCI emulation and because the BAR is no
longer 0, we write back to the BAR the value that the guest used to get the
size. As a result, the guest will think that the ROM size is 0x800 after
the subsequent read and we end up unintentionally exposing to the guest a
BAR which we don't emulate.

Let's fix this by ignoring writes to the expansion ROM BAR.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>