MdeModulePkg: Leak Memory if Not RW on FreePagesHEADmaster

Currently, if the DebugClearMemory bit is set in the
PcdDebugPropertyMask, CoreConvertPagesEx will attempt to write
a pattern to the pages being freed. However, it does not check
that the page is writeable, which will cause a page fault if not.
Furthermore, if NX protections are not enabled, the core does not
ensure that any freed pages are RW, which is the state expected
when they are allocated next. If they are not RW, the allocating
driver will crash trying to use them.

This patch updates the page freeing code to query the memory
attributes protocol, if present, for the attributes. If this call
fails or the attributes are not RW at a minimum, the core leaks
the memory (returning success to the caller). If the memory
attribute protocol is not present (either because a platform doesn't
produce it or it is before the protocol has been produced, the core
continues with freeing memory. This is either before the CPU Arch
protocol is available (so drivers can't change memory attributes) or
otherwise matches existing behavior. This was deemed the best
approach to let memory that can't be guaranteed to be RW leak
instead of letting a driver crash when allocating it. It was deemed
less brittle to simply leak the memory instead of attempting to
change the attributes.

Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>

0 files changed, 0 insertions, 0 deletions