MdeModulePkg: Fix bug of AllocatePages for large alignment

DescEnd will be clipped for alignment in CoreFindFreePagesI, and it
may fall below DescStart, when alignment is more than 16KB (included)
and both DescStart and original DescEnd fall into a single range of
such alignment. This results in a huge size (Negative number in
unsigned type) for this descriptor, fulfilling the allocation
requirement but failing to run ConvertPages; at last it causes
occasional failure of AllocatePages.

A simple comparison is added to ensure we would never get a negative
number.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17575 6f19259b-4bc3-4df7-8a09-765794883524

diff --git a/MdeModulePkg/Core/Dxe/Mem/Page.c b/MdeModulePkg/Core/Dxe/Mem/Page.c
index a92c865e171677d1e196ff7c529e19d6d163d944..f2efaf12787b072b10e273d40e82f38acc42e772 100644 (file)
--- a/MdeModulePkg/Core/Dxe/Mem/Page.c
+++ b/MdeModulePkg/Core/Dxe/Mem/Page.c
@@ -1051,6 +1051,11 @@ CoreFindFreePagesI (
 \r
     DescEnd = ((DescEnd + 1) & (~(Alignment - 1))) - 1;\r
 \r
+    // Skip if DescEnd is less than DescStart after alignment clipping\r
+    if (DescEnd < DescStart) {\r
+      continue;\r
+    }\r
+\r
     //\r
     // Compute the number of bytes we can used from this\r
     // descriptor, and see it's enough to satisfy the request\r