Revision: 14218
http://edk2.svn.sourceforge.net/edk2/?rev=14218&view=rev
Author: mdkinney
Date: 2013-03-22 21:20:07 +0000 (Fri, 22 Mar 2013)
Log Message:
-----------
Guarantee that free memory in the 4K page starting at address 0 is always
cleared to 0. The algorithm is to clear page zero if it is registered with the
DXE Core with type EfiConventionalMemory, and to also clear page zero if it is
freed using the UEFI Boot Service FreePages(). This patch improves OS
compatibility for OSes that may evaluate page 0 for legacy data structures.
Before this patch, free memory may contain random values which induces random
boot failures for some OSes. This patch may also help find NULL pointer bugs
sooner because all of the fields in a data structure dereferenced through NULL
will also be NULL now.
Signed-off-by: Michael Kinney <[email protected]>
Reviewed-by: Laszlo Ersek <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>
Modified Paths:
--------------
trunk/edk2/MdeModulePkg/Core/Dxe/Mem/Page.c
Modified: trunk/edk2/MdeModulePkg/Core/Dxe/Mem/Page.c
===================================================================
--- trunk/edk2/MdeModulePkg/Core/Dxe/Mem/Page.c 2013-03-22 21:18:02 UTC (rev
14217)
+++ trunk/edk2/MdeModulePkg/Core/Dxe/Mem/Page.c 2013-03-22 21:20:07 UTC (rev
14218)
@@ -177,8 +177,21 @@
ASSERT_LOCKED (&gMemoryLock);
DEBUG ((DEBUG_PAGE, "AddRange: %lx-%lx to %d\n", Start, End, Type));
-
+
//
+ // If memory of type EfiConventionalMemory is being added that includes the
page
+ // starting at address 0, then zero the page starting at address 0. This
has
+ // two benifits. It helps find NULL pointer bugs and it also maximizes
+ // compatibility with operating systems that may evaluate memory in this
page
+ // for legacy data structures. If memory of any other type is added
starting
+ // at address 0, then do not zero the page at address 0 because the page is
being
+ // used for other purposes.
+ //
+ if (Type == EfiConventionalMemory && Start == 0 && (End >= EFI_PAGE_SIZE -
1)) {
+ SetMem ((VOID *)(UINTN)Start, EFI_PAGE_SIZE, 0);
+ }
+
+ //
// Memory map being altered so updated key
//
mMemoryMapKey += 1;
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