Commit ac4766be authored by Marco Elver's avatar Marco Elver Committed by Linus Torvalds
Browse files

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: 7b861a53 ("kasan: Bump required compiler version")
Fixes: acf7b0bf

 ("kasan: Fix required compiler version")
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarAndrey 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7a3767f8
......@@ -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
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.
......
......@@ -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
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 @@ 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.
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 @@ 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
......
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