[PATCH] MdeModulePkg/DxeCore: deal with allocations spanning several memmap entries

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

When attempting to perform page allocations using AllocateAddress, we
fail to check whether the entire region is free before splitting the
region. This may lead to memory being leaked further into the routine,
when it turns out that one of the memory map entries intersected by the
region is already occupied. In this case, prior conversions are not rolled
back.

For instance, starting from this situation

0x000040000000-0x00004007ffff [ConventionalMemory ]
0x000040080000-0x00004009ffff [Boot Data          ]
0x0000400a0000-0x000047ffffff [ConventionalMemory ]

a failed EfiLoaderData allocation @ 0x40000000 that covers the BootData
region will fail, but leave the first part of the allocation converted,
so we end up with

0x000040000000-0x00004007ffff [Loader Data        ]
0x000040080000-0x00004009ffff [Boot Data          ]
0x0000400a0000-0x000047ffffff [ConventionalMemory ]

even though the AllocatePages() call returned an error.

So let's check beforehand that AllocateAddress allocations are covered
by a single memory map entry, so that it either succeeds or fails
completely, rather than leaking allocations.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 MdeModulePkg/Core/Dxe/Mem/Page.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/MdeModulePkg/Core/Dxe/Mem/Page.c b/MdeModulePkg/Core/Dxe/Mem/Page.c
index 260a30a214c7..92306b2f1b45 100644
--- a/MdeModulePkg/Core/Dxe/Mem/Page.c
+++ b/MdeModulePkg/Core/Dxe/Mem/Page.c
@@ -755,6 +755,17 @@ CoreConvertPagesEx (
     }
 
     //
+    // If we are converting the type of the range from EfiConventionalMemory to
+    // another type, we have to ensure that the entire range is covered by a
+    // single entry.
+    //
+    if (ChangingType && (NewType != EfiConventionalMemory)) {
+      if (Entry->Start > End || Entry->End < End) {
+        DEBUG ((DEBUG_ERROR | DEBUG_PAGE, "ConvertPages: range %lx - %lx covers multiple entries\n", Start, End));
+        return EFI_NOT_FOUND;
+      }
+    }
+    //
     // Convert range to the end, or to the end of the descriptor
     // if that's all we've got
     //
-- 
2.7.4