On 08/01/19 01:46, Laszlo Ersek wrote: > So ultimately, I would argue for the following patch series: > > - patch#1: Revert commit c60d36b4, and explain why, in the commit > message. > > - patch#2: Introduce the new PCD, also mentioning MMIO. > > - Patch#3: modify *all* of the following functions, internally, to > return immediately, if "mSmmAccessOut" is TRUE: > > - GetUefiMemoryMap() > - SetUefiMemMapAttributes() > - IsSmmCommBufferForbiddenAddress() > > Basically, the new PCD should short-circuit all three functions > declared in "PiSmmCpuDxeSmm.h" by commit d2fc7711136a.
Sigh, why is this so friggin complicated. The functions added by commit d2fc7711136a were extended with the following commits, later: * ac6613db4697 ("UefiCpuPkg/PiSmmCpu: Check for untested memory in GCD", 2018-07-26) The commit message says, "It treats GCD untested memory as invalid SMM communication buffer". * 8a2e1a9d54ee ("UefiCpuPkg/PiSmmCpu: Check EFI_RUNTIME_RO in UEFI mem attrib table.", 2018-07-26) The commit message says, "It treats the UEFI runtime page with EFI_MEMORY_RO attribute as invalid SMM communication buffer. Both of these commits come from the patch series [edk2] [PATCH 0/6] Check untested memory and EFI_MEMORY_RO http://mid.mail-archive.com/20180720052626.24932-1-hao.a.wu@intel.com https://lists.01.org/pipermail/edk2-devel/2018-July/027326.html And now the question becomes: when a platform permits "access-out", does it also enable access to untested memory, and EFI_MEMORY_RO? (a) If the answer is yes, then short-circuiting the three functions that I listed, on (mSmmAccessOut == TRUE), *immediately* after entering them, is correct. (b) If the answer is no -- that is, access-out should *continue* preventing access to untested memory, and EFI_MEMORY_RO -- then we cannot completely short-circuit the functions that I listed. Instead, we can only short-circuit those parts that work with the "mUefiMemoryMap" variable. The current description of the PCD suggests that (b) is the right approach. Thanks, Laszlo -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#44708): https://edk2.groups.io/g/devel/message/44708 Mute This Topic: https://groups.io/mt/32668874/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-