Hi Laszlo Thanks for the reminder. Hi William I try to your answer below. Feel free to let me know if you have more question.
For more detail information on how we protect SMRAM, please refer to https://www.gitbook.com/book/edk2-docs/a-tour-beyond-bios-memory-protection-in-uefi-bios/details Thank you Yao Jiewen From: Laszlo Ersek [mailto:ler...@redhat.com] Sent: Friday, March 24, 2017 11:58 PM To: William Tambe <tambewill...@gmail.com>; Yao, Jiewen <jiewen....@intel.com> Cc: edk2-devel@lists.01.org Subject: Re: [edk2] Page Table initialization and update in SMM mode Jiewen, On 03/22/17 15:14, William Tambe wrote: > Dear all, > > When building OVMF with SMM_REQUIRE: > > - Would you know where in the code base the Page Table set in the Cr3 > register is initialized during boot ? [Jiewen] UefiCpuPkg\PiSmmCpuDxeSmm\MpService.c: InitializeMpServiceData() // // Create page tables // Cr3 = SmmInitPageTable (); > > - Where does it get updated when a new page needs to be allocated or freed ? [Jiewen] We do not update page table on allocation/free. Instead PiSmmCpu driver updates page table once, after ready to lock. UefiCpuPkg\PiSmmCpuDxeSmm\PiSmmCpuDxeSmm.c: PerformRemainingTasks() // // Create a mix of 2MB and 4KB page table. Update some memory ranges absent and execute-disable. // InitPaging (); // // Mark critical region to be read-only in page table // SetMemMapAttributes (); // // For outside SMRAM, we only map SMM communication buffer or MMIO. // SetUefiMemMapAttributes (); // // Set page table itself to be read-only // SetPageTableAttributes (); > > - Or is there a hook I can register myself to in order to get a chance to > review an entry to be added or removed from the Page Tables ? [Jiewen] You can register a ready to boot event in your SMM driver and dump page table, which is the final page table in SMM. (That is what our internal test case does. :)) can you please help answer these questions? I seem to remember that we discussed code around this when we were looking into the SMM stack overflow experienced with OVMF: 509f8425b75d UefiCpuPkg: change PcdCpuSmmStackGuard default to TRUE 0d0c245dfb14 OvmfPkg: set SMM stack size to 16KB William: I suggest to check out the following files: UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c and/or to grep the code for "PcdCpuSmmStackGuard", to get a feel for what to investigate. Thanks Laszlo _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
