linux-kernel - [PATCH mm] kfence: zero guard page after out-of-bounds access

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Message-Id: <20210312121653.348518-1-elver@google.com>
Date:   Fri, 12 Mar 2021 13:16:53 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, akpm@...ux-foundation.org
Cc:     glider@...gle.com, dvyukov@...gle.com, andreyknvl@...gle.com,
        jannh@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com
Subject: [PATCH mm] 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.

Signed-off-by: Marco Elver <elver@...gle.com>
---
 mm/kfence/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 3b8ec938470a..f7106f28443d 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -371,6 +371,7 @@ static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool z
 
 	/* 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;
 	}
-- 
2.31.0.rc2.261.g7f71774620-goog