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Date: Tue, 31 Jan 2017 12:24:22 -0800
From: Kees Cook <>
Cc: Kees Cook <>,
	Emese Revfy <>,
	Arnd Bergmann <>,
	Josh Triplett <>,,,,,,,,,,,,,
Subject: [PATCH v5 4/4] initify: Mark functions with the __unverified_nocapture attribute

From: Emese Revfy <>

The initify plugin attempts to analyze function arguments that have been
marked correctly with the __nocapture attribute. However, due to code
complexity, this is not always possible to verify. As a result, some
__nocapture attributes need to be marked as excluded from the automatic
verification. To do this, the __unverified_nocapture attribute is added.
It is intedned to only be used on function parameters that are difficult
for the plugin to analyze.

Signed-off-by: Emese Revfy <>
Signed-off-by: Kees Cook <>
 include/linux/compiler-gcc.h | 8 ++++++++
 include/linux/compiler.h     | 4 ++++
 lib/vsprintf.c               | 4 ++--
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index cd4e9ffb00a7..fc0495e849ff 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -204,9 +204,17 @@
  * been unmapped from memory. In order to identify functions that are confirmed
  * to not capture their arguments, the __nocapture() attribute is used so that
  * initify can better identify candidate variables.
+ *
+ * Arguments marked in this way are verified by the plugin, but sometimes
+ * code complexity and other limitiations will cause initify to not be able
+ * to check it correctly. For these cases, the __unverified_nocapture
+ * attribute can be added to disable this checking, overriding the plugin
+ * logic for cases that have been manually verified. This should not need
+ * to be used very often.
 #define __nocapture(...) __attribute__((nocapture(__VA_ARGS__)))
+#define __unverified_nocapture(...) __attribute__((unverified_nocapture(__VA_ARGS__)))
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 8b3dcc790bb6..1bde420f07bb 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -437,6 +437,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 # define __nocapture(...)
+#ifndef __unverified_nocapture
+# define __unverified_nocapture(...)
  * Tell gcc if a function is cold. The compiler will assume any path
  * directly leading to the call is unlikely.
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index a192761d338a..cb964b51f9f8 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -118,7 +118,7 @@ long long simple_strtoll(const char *cp, char **endp, unsigned int base)
-static noinline_for_stack __nocapture(1)
+static noinline_for_stack __nocapture(1) __unverified_nocapture(1)
 int skip_atoi(const char **s)
 	int i = 0;
@@ -1570,7 +1570,7 @@ int kptr_restrict __read_mostly;
  * function pointers are really function descriptors, which contain a
  * pointer to the real address.
-static noinline_for_stack __nocapture(1)
+static noinline_for_stack __nocapture(1) __unverified_nocapture(1)
 char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	      struct printf_spec spec)

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