[PATCH v11 1/6] kasan: allow an architecture to disable inline instrumentation

Daniel Axtens
2021-03-19T14:41:24Z

For annoying architectural reasons, it's very difficult to support inline
instrumentation on powerpc64.

Add a Kconfig flag to allow an arch to disable inline. (It's a bit
annoying to be 'backwards', but I'm not aware of any way to have
an arch force a symbol to be 'n', rather than 'y'.)

We also disable stack instrumentation in this case as it does things that
are functionally equivalent to inline instrumentation, namely adding
code that touches the shadow directly without going through a C helper.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
lib/Kconfig.kasan | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cffc2ebbf185..7e237dbb6df3 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -12,6 +12,9 @@ config HAVE_ARCH_KASAN_HW_TAGS
config HAVE_ARCH_KASAN_VMALLOC
bool

+config ARCH_DISABLE_KASAN_INLINE
+ def_bool n
+
config CC_HAS_KASAN_GENERIC
def_bool $(cc-option, -fsanitize=kernel-address)

@@ -130,6 +133,7 @@ config KASAN_OUTLINE

config KASAN_INLINE
bool "Inline instrumentation"
+ depends on !ARCH_DISABLE_KASAN_INLINE
help
Compiler directly inserts code checking shadow memory before
memory accesses. This is faster than outline (in some workloads
@@ -142,6 +146,7 @@ config KASAN_STACK
bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
depends on KASAN_GENERIC || KASAN_SW_TAGS
default y if CC_IS_GCC
+ depends on !ARCH_DISABLE_KASAN_INLINE
help
The LLVM stack address sanitizer has a know problem that
causes excessive stack usage in a lot of functions, see
@@ -154,6 +159,9 @@ config KASAN_STACK
but clang users can still enable it for builds without
CONFIG_COMPILE_TEST. On gcc it is assumed to always be safe
to use and enabled by default.
+ If the architecture disables inline instrumentation, this is
+ also disabled as it adds inline-style instrumentation that
+ is run unconditionally.

config KASAN_SW_TAGS_IDENTIFY
bool "Enable memory corruption identification"
--
2.27.0