[PATCH V2 2/3] x86/mm/pti: issue warning when mapping large pmd beyond specifid range

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

When PTI_CLONE_PTE, the caller doesn't want to expose pages beyond specifid
range and it worths a warning.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 arch/x86/mm/pti.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7ee99ef13a99..cd6da1d42ba9 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -356,6 +356,13 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 			 * caller, so we just simply align it here.
 			 */
 			addr = round_down(addr, PMD_SIZE);
+			/*
+			 * Mapping large pmd beyond [start, end) may expose
+			 * secrets to user-space when it wants to clone ptes
+			 * only.
+			 */
+			WARN_ON_ONCE(level == PTI_CLONE_PTE &&
+				     (addr < start || end < addr + PMD_SIZE));
 
 			target_pmd = pti_user_pagetable_walk_pmd(addr);
 			if (WARN_ON(!target_pmd))
-- 
2.19.1.6.gb485710b