[PATCH V2 1/3] x86/mm/pti: handle unaligned address for pmd clone in pti_clone_pagetable()

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <laijs@linux.alibaba.com>

The commit 825d0b73cd752("x86/mm/pti: Handle unaligned address gracefully
in pti_clone_pagetable()") handles unaligned address well for unmapped
PUD/PMD etc. But unaligned address for mapped pmd also needs to
be aware.

For mapped pmd, if @addr is not aligned to PMD_SIZE, the next pmd
(PTI_CLONE_PMD or the next pmd is large) or the last ptes (PTI_CLONE_PTE)
in the next pmd will not be cloned when @end < @addr + PMD_SIZE in the
current logic in the code.

It is not a good idea to force alignment in the caller due to one of
the cases (see the comments in the code), so it just handles the alignment
in pti_clone_pagetable().

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/mm/pti.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 1aab92930569..7ee99ef13a99 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -342,6 +342,21 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 		}
 
 		if (pmd_large(*pmd) || level == PTI_CLONE_PMD) {
+			/*
+			 * pti_clone_kernel_text() might be called with
+			 * @start not aligned to PMD_SIZE. We need to make
+			 * it aligned, otherwise the next pmd or last ptes
+			 * are not cloned when @end < @addr + PMD_SIZE.
+			 *
+			 * We can't force pti_clone_kernel_text() to align
+			 * the @addr to PMD_SIZE when level == PTI_CLONE_PTE.
+			 * But the problem can still possible exist when the
+			 * first pmd is large. And it is not a good idea to
+			 * check whether the first pmd is large or not in the
+			 * caller, so we just simply align it here.
+			 */
+			addr = round_down(addr, PMD_SIZE);
+
 			target_pmd = pti_user_pagetable_walk_pmd(addr);
 			if (WARN_ON(!target_pmd))
 				return;
-- 
2.19.1.6.gb485710b