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ArmPkg/ArmMmuLib AARCH64: preserve attributes when replacing a table entry 

Currently, depending on the size of the region being (re)mapped, the
page table manipulation code may replace a table entry with a block entry,
even if the existing table entry uses different mapping attributes to
describe different parts of the region it covers. This is undesirable, and
instead, we should avoid doing so unless we are disregarding the original
attributes anyway. And if we make such a replacement, we should free all
the page tables that have become orphaned in the process.

So let's implement this, by taking the table entry path through the code
for block sized regions if a table entry already exists, and the clear
mask is set (which means we are preserving attributes from the existing
mapping). And when we do replace a table entry with a block entry, free
all the pages that are no longer referenced.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Ashish Singhal <ashishsingha@nvidia.com>
Tested-by: Ashish Singhal <ashishsingha@nvidia.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Ard Biesheuvel 2020-03-07 13:35:55 +01:00 committed by mergify[bot]
parent 5fc899535e
commit f7079d1bc1
1 changed files with 21 additions and 4 deletions
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25
ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
View File

@ -229,8 +229,12 @@ UpdateRegionMappingRecursive (
// than a block, and recurse to create the block or page entries at
// the next level. No block mappings are allowed at all at level 0,
// so in that case, we have to recurse unconditionally.
// If we are changing a table entry and the AttributeClearMask is non-zero,
// we cannot replace it with a block entry without potentially losing
// attribute information, so keep the table entry in that case.
//
if (Level == 0 || ((RegionStart | BlockEnd) & BlockMask) != 0) {
if (Level == 0 || ((RegionStart | BlockEnd) & BlockMask) != 0 ||
(IsTableEntry (*Entry, Level) && AttributeClearMask != 0)) {
ASSERT (Level < 3);
if (!IsTableEntry (*Entry, Level)) {
@ -251,6 +255,8 @@ UpdateRegionMappingRecursive (
InvalidateDataCacheRange (TranslationTable, EFI_PAGE_SIZE);
}
ZeroMem (TranslationTable, EFI_PAGE_SIZE);
if (IsBlockEntry (*Entry, Level)) {
//
// We are splitting an existing block entry, so we have to populate
@ -268,8 +274,6 @@ UpdateRegionMappingRecursive (
FreePages (TranslationTable, 1);
return Status;
}
} else {
ZeroMem (TranslationTable, EFI_PAGE_SIZE);
}
} else {
TranslationTable = (VOID *)(UINTN)(*Entry & TT_ADDRESS_MASK_BLOCK_ENTRY);
@ -306,7 +310,20 @@ UpdateRegionMappingRecursive (
EntryValue |= (Level == 3) ? TT_TYPE_BLOCK_ENTRY_LEVEL3
: TT_TYPE_BLOCK_ENTRY;
ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);
if (IsTableEntry (*Entry, Level)) {
//
// We are replacing a table entry with a block entry. This is only
// possible if we are keeping none of the original attributes.
// We can free the table entry's page table, and all the ones below
// it, since we are dropping the only possible reference to it.
//
ASSERT (AttributeClearMask == 0);
TranslationTable = (VOID *)(UINTN)(*Entry & TT_ADDRESS_MASK_BLOCK_ENTRY);
ReplaceTableEntry (Entry, EntryValue, RegionStart, TRUE);
FreePageTablesRecursive (TranslationTable, Level + 1);
} else {
ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);
}
}
}
return EFI_SUCCESS;