linux-kernel - [PATCH 1/2] lib/stackdepot: kmsan: mark API outputs as initialized

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Date:   Mon,  6 Mar 2023 12:13:21 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, elver@...gle.com, dvyukov@...gle.com,
        kasan-dev@...glegroups.com, Andrey Konovalov <andreyknvl@...il.com>
Subject: [PATCH 1/2] lib/stackdepot: kmsan: mark API outputs as initialized

KMSAN does not instrument stackdepot and may treat memory allocated by
it as uninitialized. This is not a problem for KMSAN itself, because its
functions calling stackdepot API are also not instrumented.
But other kernel features (e.g. netdev tracker) may access stack depot
from instrumented code, which will lead to false positives, unless we
explicitly mark stackdepot outputs as initialized.

Cc: Andrey Konovalov <andreyknvl@...il.com>
Cc: Marco Elver <elver@...gle.com>
Suggested-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
 lib/stackdepot.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 036da8e295d19..2f5aa851834eb 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -17,6 +17,7 @@
 #include <linux/gfp.h>
 #include <linux/jhash.h>
 #include <linux/kernel.h>
+#include <linux/kmsan.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/percpu.h>
@@ -306,6 +307,11 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 	stack->handle.extra = 0;
 	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
 	pool_offset += required_size;
+	/*
+	 * Let KMSAN know the stored stack record is initialized. This shall
+	 * prevent false positive reports if instrumented code accesses it.
+	 */
+	kmsan_unpoison_memory(stack, required_size);
 
 	return stack;
 }
@@ -465,6 +471,12 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 	struct stack_record *stack;
 
 	*entries = NULL;
+	/*
+	 * Let KMSAN know *entries is initialized. This shall prevent false
+	 * positive reports if instrumented code accesses it.
+	 */
+	kmsan_unpoison_memory(entries, sizeof(*entries));
+
 	if (!handle)
 		return 0;
 
-- 
2.40.0.rc0.216.gc4246ad0f0-goog