efi: Align unaccepted memory range to page boundary

The accept_memory() and range_contains_unaccepted_memory() functions
employ a "guard page" logic to prevent crashes with load_unaligned_zeropad().
This logic extends the range to be accepted (or checked) by one unit_size
if the end of the range is aligned to a unit_size boundary.

However, if the caller passes a range that is not page-aligned, the
'end' of the range might not be numerically aligned to unit_size, even
if it covers the last page of a unit. This causes the "if (!(end % unit_size))"
check to fail, skipping the necessary extension and leaving the next
unit unaccepted, which can lead to a kernel panic when accessed by
load_unaligned_zeropad().

Align the start address down and the size up to the nearest page
boundary before performing the unit_size alignment check. This ensures
that the guard unit is correctly added when the range effectively ends
on a unit boundary.

Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Author: Kiryl Shutsemau (Meta)

drivers/firmware/efi/unaccepted_memory.c

@@ -35,14 +35,17 @@ void accept_memory(phys_addr_t start, unsigned long size)
 	struct efi_unaccepted_memory *unaccepted;
 	unsigned long range_start, range_end;
 	struct accept_range range, *entry;
-	phys_addr_t end = start + size;
 	unsigned long flags;
+	phys_addr_t end;
 	u64 unit_size;
 
 	unaccepted = efi_get_unaccepted_table();
 	if (!unaccepted)
 		return;
 
+	end = PAGE_ALIGN(start + size);
+	start = PAGE_ALIGN_DOWN(start);
+
 	unit_size = unaccepted->unit_size;
 
 	/*
@@ -160,15 +163,18 @@ void accept_memory(phys_addr_t start, unsigned long size)
 bool range_contains_unaccepted_memory(phys_addr_t start, unsigned long size)
 {
 	struct efi_unaccepted_memory *unaccepted;
-	phys_addr_t end = start + size;
 	unsigned long flags;
 	bool ret = false;
+	phys_addr_t end;
 	u64 unit_size;
 
 	unaccepted = efi_get_unaccepted_table();
 	if (!unaccepted)
 		return false;
 
+	end = PAGE_ALIGN(start + size);
+	start = PAGE_ALIGN_DOWN(start);
+
 	unit_size = unaccepted->unit_size;
 
 	/*