On Fri, 23 Oct 2015 08:56:26 +0200 Gerd Hoffmann <kra...@redhat.com> wrote:
> Hi, > > > One complication I thought of was that it might be tricky to deal > > with the implications of allowing this DMA to specify any old > > address to fill with fw_cfg data. > > > > So, for example, since Red Hat is working on SMM. Would a DMA to > > SMRAM be protected? > > > > I haven't watched the fw_cfg DMA discussion too closely, but has > > this been thought about? > > Yes. That problem isn't new and it isn't specific to fw_cfg. You > also don't want grant dma access to smram/tseg to your ide/sata/scsi > controller or NIC. > > > One idea I had was that near the end of the firmware boot, the > > firmware could trigger fw_cfg in QEMU to stop supporting DMA until a > > reset. > > Should not be needed. We have address spaces in qemu, and the > smram/tseg regions are explicitly excluded (when enabled) from > dma-able memory. > > mark: when writing a fw_cfg_dma tests it is a good idea to add a > testcase for this, so make sure this works as intended and to avoid > security-sensitive regressions. Noted, thanks Marc > cheers, > Gerd > >
