lkml.org 
[lkml]   [2019]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] [EFI,PCI] Allow disabling PCI busmastering on bridges during boot
On Tue, Dec 3, 2019 at 11:11 PM Laszlo Ersek <lersek@redhat.com> wrote:
> But in this case, we'd have to insert the PPB clearing *before* the
> (platform's) IOMMU driver's EBS handler (because the latter is going to
> deny, not permit, everything); and we can't modify the IOMMU driver.
>
> I guess we could install an EBS handler with TPL_NOTIFY (PciIo usage
> appears permitted at TPL_NOTIFY, from "Table 27. TPL Restrictions"). But:
> - if the IOMMU driver's EBS handler is also to be enqueued at
> TPL_NOTIFY, then the order will be unspecified
> - if a PCI driver sets up an EBS handler at TPL_CALLBACK, then in our
> handler we could shut down a PPB in front of a device bound by that
> driver too early.

Yeah, that's my concern - doing this more correctly seems to leave us
in a situation where we're no longer able to make guarantees about the
security properties of the feature. I think I prefer going with
something that's guaranteed to give us the properties we want, even at
the expense of some compatibility - users who want this can validate
it against their platform.

\
 
 \ /
  Last update: 2019-12-04 20:31    [W:0.088 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site