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: 7b861a53e46b ("kasan: Bump required compiler version")
Fixes: acf7b0bf7dcf ("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>
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index c652d740..15a2a53e 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -13,11 +13,8 @@
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
-out-of-bounds accesses for stack and global variables and for inline
-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.
+8.3.0 or later. With Clang it requires version 7.0.0 or later, but detection of
+out-of-bounds accesses for global variables is only supported since Clang 11.
Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 89053def..047b53d 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -40,6 +40,7 @@
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 @@
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
- out-of-bounds accesses for stack and global variables and for inline
- instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
- version 3.7.0 or later and it doesn't support detection of
- out-of-bounds accesses for global variables yet.
+
+ This mode is supported in both GCC and Clang. With GCC it requires
+ version 8.3.0 or later. With Clang it requires version 7.0.0 or
+ later, but detection of out-of-bounds accesses for global variables
+ is supported only since Clang 11.
+
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 @@
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.
- This mode requires Clang version 7.0.0 or later.
+ is only supported for arm64. This mode requires Clang version 7.0.0
+ 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 @@
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
