OvmfPkg/BaseMemEncryptSevLib: Fix read-only pagetable support

SetMemoryEncDec() ensures that any newly created pagetable pages are
marked read-only upon completion of the pagetable changes. This is done
by calling EnablePageTableProtection(). EnablePageTableProtection()
invokes SetPageTablePoolReadOnly() which expects the input PageTableBase
parameter to point to the beginning of the level 4 pagetable as it
calculates the offset/index into the pagetable based on the input address.

However, there is a bug that is seen when the input address is above
512GB. SetMemoryEncDec() uses the PageMapLevel4Entry variable when it
invokes EnablePageTableProtection(), which points to the start of the
level 4 pagetable if the address is below 512GB. Once above that range,
PageMapLevel4Entry points past the start of the pagetable. This causes
SetPageTablePoolReadOnly() to improperly address pagetable entries.

This was recently exposed when 7735ed4f8eb3 ("OvmfPkg/PlatformInitLib:
Set dynamic MMIO window size to 1/4") pushed the MMIO range above 512GB.

Fix the issue by always using the Cr3BaseAddress value when calling
EnablePageTableProtection().

Since PageMapLevel4Entry is never used outside of the loop anymore,
remove the initialization to NULL. Also, the check for Cr3BaseAddress
being NULL does not need to be done inside the loop, so move it to outside
the loop (which will suppress incorrect compiler/analyzer warnings).

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

0 files changed, 0 insertions, 0 deletions