Hi,
there's this code in CoreAllocateSpace(), in "MdeModulePkg/Core/Dxe/Gcd/Gcd.c":
1156 if (GcdAllocateType == EfiGcdAllocateMaxAddressSearchTopDown ||
1157 GcdAllocateType == EfiGcdAllocateAnySearchTopDown) {
1158 if ((Entry->BaseAddress + Length) > MaxAddress) {
1159 continue;
1160 }
1161 if (Length > (Entry->EndAddress + 1)) {
1162 Status = EFI_NOT_FOUND;
1163 goto Done;
1164 }
1165 if (Entry->EndAddress > MaxAddress) {
1166 *BaseAddress = MaxAddress;
1167 } else {
1168 *BaseAddress = Entry->EndAddress;
1169 }
1170 *BaseAddress = (*BaseAddress + 1 - Length) & (~AlignmentMask);
1171 } else {
1172 *BaseAddress = (Entry->BaseAddress + AlignmentMask) &
(~AlignmentMask);
1173 if ((*BaseAddress + Length - 1) > MaxAddress) {
1174 Status = EFI_NOT_FOUND;
1175 goto Done;
1176 }
1177 }
When serching bottom-up (which is the more usual case), the check on line 1173
considers the fact that MaxAddress is an *inclusive* limit, while Length is an
*exclusive* size. That is, the following situation is valid:
BaseAddress + Length == MaxAddress + 1
which is equivalent to
BaseAddress + Length - 1 == MaxAddress
Hence the check on line 1173
BaseAddress + Length - 1 > MaxAddress
is a correct check for invalidity. Okay.
However, the invalidity check on line 1158 seems wrong, for the top-down search:
Entry->BaseAddress + Length > MaxAddress
is too strict (off-by-one). Namely,
BaseAddress + Length == MaxAddress + 1
is a valid condition (see above), but it triggers:
BaseAddress + Length == MaxAddress + 1 > MaxAddress
I noticed this error by printing GCD maps (DEBUG_GCD) and using
EfiGcdAllocateMaxAddressSearchTopDown.
Thanks
Laszlo
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