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

[Daniel Axtens]

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 at 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