[PATCH RFC v2 3/6] mm: Integrate SLAB_QUARANTINE with init_on_free

[Alexander Popov <alex.popov@linux.com>]

Having slab quarantine without memory erasing is harmful.
If the quarantined objects are not cleaned and contain data, then:
  1. they will be useful for use-after-free exploitation,
  2. there is no chance to detect use-after-free access.
So we want the quarantined objects to be erased.
Enable init_on_free that cleans objects before placing them into
the quarantine. CONFIG_PAGE_POISONING should be disabled since it
cuts off init_on_free.

Signed-off-by: Alexander Popov <alex.popov@linux.com>
---
 init/Kconfig    |  3 ++-
 mm/page_alloc.c | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 358c8ce818f4..cd4cee71fd4e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1933,7 +1933,8 @@ config SLAB_FREELIST_HARDENED
 
 config SLAB_QUARANTINE
 	bool "Enable slab freelist quarantine"
-	depends on !KASAN && (SLAB || SLUB)
+	depends on !KASAN && (SLAB || SLUB) && !PAGE_POISONING
+	select INIT_ON_FREE_DEFAULT_ON
 	help
 	  Enable slab freelist quarantine to delay reusing of freed slab
 	  objects. If this feature is enabled, freed objects are stored
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fab5e97dc9ca..f67118e88500 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -168,6 +168,27 @@ static int __init early_init_on_alloc(char *buf)
 }
 early_param("init_on_alloc", early_init_on_alloc);
 
+#ifdef CONFIG_SLAB_QUARANTINE
+static int __init early_init_on_free(char *buf)
+{
+	/*
+	 * Having slab quarantine without memory erasing is harmful.
+	 * If the quarantined objects are not cleaned and contain data, then:
+	 *  1. they will be useful for use-after-free exploitation,
+	 *  2. use-after-free access may not be detected.
+	 * So we want the quarantined objects to be erased.
+	 *
+	 * Enable init_on_free that cleans objects before placing them into
+	 * the quarantine. CONFIG_PAGE_POISONING should be disabled since it
+	 * cuts off init_on_free.
+	 */
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON));
+	BUILD_BUG_ON(IS_ENABLED(CONFIG_PAGE_POISONING));
+	pr_info("mem auto-init: init_on_free is on for CONFIG_SLAB_QUARANTINE\n");
+
+	return 0;
+}
+#else /* CONFIG_SLAB_QUARANTINE */
 static int __init early_init_on_free(char *buf)
 {
 	int ret;
@@ -184,6 +205,7 @@ static int __init early_init_on_free(char *buf)
 		static_branch_disable(&init_on_free);
 	return ret;
 }
+#endif /* CONFIG_SLAB_QUARANTINE */
 early_param("init_on_free", early_init_on_free);
 
 /*
-- 
2.26.2