kasan: show gcc version requirements in Kconfig and Documentation

The documentation shows a need for gcc > 4.9.2, but it's really >=.  The
Kconfig entries don't show require versions so add them.  Correct a
latter/later typo too.  Also mention that gcc 5 required to catch out of
bounds accesses to global and stack variables.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 4fecaedc80a2..777eda7d1ab4 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -10,8 +10,11 @@ config KASAN
 	help
 	  Enables kernel address sanitizer - runtime memory debugger,
 	  designed to find out-of-bounds accesses and use-after-free bugs.
-	  This is strictly debugging feature. It consumes about 1/8
-	  of available memory and brings about ~x3 performance slowdown.
+	  This is strictly a debugging feature and it requires a gcc version
+	  of 4.9.2 or later. Detection of out of bounds accesses to stack or
+	  global variables requires gcc 5.0 or later.
+	  This feature consumes about 1/8 of available memory and brings about
+	  ~x3 performance slowdown.
 	  For better error detection enable CONFIG_STACKTRACE,
 	  and add slub_debug=U to boot cmdline.
 
@@ -40,6 +43,7 @@ config KASAN_INLINE
 	  memory accesses. This is faster than outline (in some workloads
 	  it gives about x2 boost over outline instrumentation), but
 	  make kernel's .text size much bigger.
+	  This requires a gcc version of 5.0 or later.
 
 endchoice