@@ -23,6 +23,32 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
bitmap = __va(boot_params.unaccepted_memory);
range_start = start / PMD_SIZE;
+ /*
+ * load_unaligned_zeropad() can lead to unwanted loads across page
+ * boundaries. The unwanted loads are typically harmless. But, they
+ * might be made to totally unrelated or even unmapped memory.
+ * load_unaligned_zeropad() relies on exception fixup (#PF, #GP and now
+ * #VE) to recover from these unwanted loads.
+ *
+ * But, this approach does not work for unaccepted memory. For TDX, a
+ * load from unaccepted memory will not lead to a recoverable exception
+ * within the guest. The guest will exit to the VMM where the only
+ * recourse is to terminate the guest.
+ *
+ * There are two parts to fix this issue and comprehensively avoid
+ * access to unaccepted memory. Together these ensure that an extra
+ * "guard" page is accepted in addition to the memory that needs to be
+ * used:
+ *
+ * 1. Implicitly extend the range_contains_unaccepted_memory(start, end)
+ * checks up to end+2M if 'end' is aligned on a 2M boundary.
+ *
+ * 2. Implicitly extend accept_memory(start, end) to end+2M if 'end' is
+ * aligned on a 2M boundary. (immediately following this comment)
+ */
+ if (!(end % PMD_SIZE))
+ end += PMD_SIZE;
+
spin_lock_irqsave(&unaccepted_memory_lock, flags);
for_each_set_bitrange_from(range_start, range_end, bitmap,
DIV_ROUND_UP(end, PMD_SIZE)) {
@@ -46,6 +72,13 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
bitmap = __va(boot_params.unaccepted_memory);
+ /*
+ * Also consider the unaccepted state of the *next* page. See fix #1 in
+ * the comment on load_unaligned_zeropad() in accept_memory().
+ */
+ if (!(end % PMD_SIZE))
+ end += PMD_SIZE;
+
spin_lock_irqsave(&unaccepted_memory_lock, flags);
while (start < end) {
if (test_bit(start / PMD_SIZE, bitmap)) {
@@ -715,6 +715,13 @@ static efi_status_t allocate_unaccepted_bitmap(struct boot_params *params,
return EFI_SUCCESS;
}
+ /*
+ * range_contains_unaccepted_memory() may need to check one 2M chunk
+ * beyond the end of RAM to deal with load_unaligned_zeropad(). Make
+ * sure that the bitmap is large enough handle it.
+ */
+ max_addr += PMD_SIZE;
+
/*
* If unaccepted memory is present, allocate a bitmap to track what
* memory has to be accepted before access.