kasan: update required compiler versions in documentation

Updates the recently changed compiler requirements for KASAN.  In
particular, we require GCC >= 8.3.0, and add a note that Clang 11 supports
OOB detection of globals.

Fixes: 7b861a53e4 ("kasan: Bump required compiler version")
Fixes: acf7b0bf7d ("kasan: Fix required compiler version")
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Walter Wu <walter-zh.wu@mediatek.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Axtens <dja@axtens.net>
Link: http://lkml.kernel.org/r/20200629104157.3242503-2-elver@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/dev-tools/kasan.rst

@@ -13,11 +13,8 @@ KASAN uses compile-time instrumentation to insert validity checks before every
 memory access, and therefore requires a compiler version that supports that.
 
 Generic KASAN is supported in both GCC and Clang. With GCC it requires version
-4.9.2 or later for basic support and version 5.0 or later for detection of
+8.3.0 or later. With Clang it requires version 7.0.0 or later, but detection of
-out-of-bounds accesses for stack and global variables and for inline
+out-of-bounds accesses for global variables is only supported since Clang 11.
-instrumentation mode (see the Usage section). With Clang it requires version
-7.0.0 or later and it doesn't support detection of out-of-bounds accesses for
-global variables yet.
 
 Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
 

lib/Kconfig.kasan

@@ -40,6 +40,7 @@ choice
 	  software tag-based KASAN (a version based on software memory
 	  tagging, arm64 only, similar to userspace HWASan, enabled with
 	  CONFIG_KASAN_SW_TAGS).
+
 	  Both generic and tag-based KASAN are strictly debugging features.
 
 config KASAN_GENERIC
@@ -51,16 +52,18 @@ config KASAN_GENERIC
 	select STACKDEPOT
 	help
 	  Enables generic KASAN mode.
-	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
+
-	  or later for basic support and version 5.0 or later for detection of
+	  This mode is supported in both GCC and Clang. With GCC it requires
-	  out-of-bounds accesses for stack and global variables and for inline
+	  version 8.3.0 or later. With Clang it requires version 7.0.0 or
-	  instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
+	  later, but detection of out-of-bounds accesses for global variables
-	  version 3.7.0 or later and it doesn't support detection of
+	  is supported only since Clang 11.
-	  out-of-bounds accesses for global variables yet.
+
 	  This mode consumes about 1/8th of available memory at kernel start
 	  and introduces an overhead of ~x1.5 for the rest of the allocations.
 	  The performance slowdown is ~x3.
+
 	  For better error detection enable CONFIG_STACKTRACE.
+
 	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
@@ -73,15 +76,19 @@ config KASAN_SW_TAGS
 	select STACKDEPOT
 	help
 	  Enables software tag-based KASAN mode.
+
 	  This mode requires Top Byte Ignore support by the CPU and therefore
-	  is only supported for arm64.
+	  is only supported for arm64. This mode requires Clang version 7.0.0
-	  This mode requires Clang version 7.0.0 or later.
+	  or later.
+
 	  This mode consumes about 1/16th of available memory at kernel start
 	  and introduces an overhead of ~20% for the rest of the allocations.
 	  This mode may potentially introduce problems relating to pointer
 	  casting and comparison, as it embeds tags into the top byte of each
 	  pointer.
+
 	  For better error detection enable CONFIG_STACKTRACE.
+
 	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
@@ -107,7 +114,6 @@ 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.
-	  For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
 
 endchoice