[140/143] kfence: zero guard page after out-of-bounds access

Commit Message

Andrew Morton May 5, 2021, 1:40 a.m. UTC

From: Marco Elver <[e-mail]>
Subject: kfence: zero guard page after out-of-bounds access

After an out-of-bounds accesses, zero the guard page before re-protecting
in kfence_guarded_free().  On one hand this helps make the failure mode of
subsequent out-of-bounds accesses more deterministic, but could also
prevent certain information leaks.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Marco Elver <[e-mail]>
Acked-by: Alexander Potapenko <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: Jann Horn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/kfence/core.c |    1 +
 1 file changed, 1 insertion(+)

Patch

--- a/mm/kfence/core.c~kfence-zero-guard-page-after-out-of-bounds-access
+++ a/mm/kfence/core.c
@@ -372,6 +372,7 @@  static void kfence_guarded_free(void *ad
 
 	/* Restore page protection if there was an OOB access. */
 	if (meta->unprotected_page) {
+		memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE);
 		kfence_protect(meta->unprotected_page);
 		meta->unprotected_page = 0;
 	}