From 91f4af6db08d4ee7fb678d4339eec8c9c666d76d Mon Sep 17 00:00:00 2001 From: Taylor Beebe Date: Tue, 30 Apr 2024 16:38:05 -0700 Subject: [PATCH] Don't set Guard Pages Before GCD Sync is Complete Description There's a window between when the CPU Arch Protocol is published and the GCD sync is complete where guard pages could be set on allocated memory and unset on freed memory. These operations should not be done until the GCD sync is complete or some free memory may have EFI_MEMORY_RP applied before the memory protection logic expects. - [x] Impacts functionality? - **Functionality** - Does the change ultimately impact how firmware functions? - Examples: Add a new library, publish a new PPI, update an algorithm, ... - [x] Impacts security? - **Security** - Does the change have a direct security impact on an application, flow, or firmware? - Examples: Crypto algorithm change, buffer overflow fix, parameter validation improvement, ... - [ ] Breaking change? - **Breaking change** - Will anyone consuming this change experience a break in build or boot behavior? - Examples: Add a new library class, move a module to a different repo, call a function in a new library class in a pre-existing module, ... - [ ] Includes tests? - **Tests** - Does the change include any explicit test code? - Examples: Unit tests, integration tests, robot tests, ... - [ ] Includes documentation? - **Documentation** - Does the change contain explicit documentation additions outside direct code modifications (and comments)? - Examples: Update readme file, add feature readme file, link to documentation on an a separate Web page, ... How This Was Tested Tested by running the DxePagingAuditTestApp on Q35 and SBSA platforms. Additionally tested by booting to Windows on Q35. Integration Instructions N/A --- MdeModulePkg/Core/Dxe/Mem/HeapGuard.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c index ff64ff27ea2..42ee9300c71 100644 --- a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c +++ b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c @@ -537,7 +537,11 @@ SetGuardPage ( { EFI_STATUS Status; - if (gCpu == NULL) { + // MU_CHANGE: Because the memory protection initialization routine + // is no longer triggered by the CPU arch protocol, check + // if the initialization routine has run before allowing + // this function to execute. + if ((gCpu == NULL) || !mGcdSyncComplete) { return; } @@ -573,7 +577,11 @@ UnsetGuardPage ( UINT64 Attributes; EFI_STATUS Status; - if (gCpu == NULL) { + // MU_CHANGE: Because the memory protection initialization routine + // is no longer triggered by the CPU arch protocol, check + // if the initialization routine has run before allowing + // this function to execute. + if ((gCpu == NULL) || !mGcdSyncComplete) { return; }