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From: Daniel Axtens <>
	Daniel Axtens <>
Subject: [PATCH v14 1/4] kasan: allow an architecture to disable inline instrumentation
Date: Thu, 17 Jun 2021 16:39:53 +1000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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.

* on ppc64 atm, the shadow lives in virtual memory and isn't accessible in
real mode. However, before we turn on virtual memory, we parse the device
tree to determine which platform and MMU we're running under. That calls
generic DT code, which is instrumented. Inline instrumentation in DT would
unconditionally attempt to touch the shadow region, which we won't have
set up yet, and would crash. We can make outline mode wait for the arch to
be ready, but we can't change what the compiler inserts for inline mode.

Signed-off-by: Daniel Axtens <>
 lib/Kconfig.kasan | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cffc2ebbf185..cb5e02d09e11 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -12,6 +12,15 @@ config HAVE_ARCH_KASAN_HW_TAGS
+	bool
+	help
+	  Sometimes an architecture might not be able to support inline
+	  instrumentation but might be able to support outline instrumentation.
+	  This option allows an architecture to prevent inline and stack
+	  instrumentation from being enabled.
 	def_bool $(cc-option, -fsanitize=kernel-address)
@@ -130,6 +139,7 @@ config KASAN_OUTLINE
 	bool "Inline instrumentation"
 	  Compiler directly inserts code checking shadow memory before
 	  memory accesses. This is faster than outline (in some workloads
@@ -141,6 +151,7 @@ endchoice
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 	default y if CC_IS_GCC
 	  The LLVM stack address sanitizer has a know problem that
@@ -154,6 +165,9 @@ 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.
 	bool "Enable memory corruption identification"

  reply	other threads:[~2021-06-17  6:40 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-17  6:39 [PATCH v14 0/4] KASAN core changes for ppc64 radix KASAN Daniel Axtens
2021-06-17  6:39 ` Daniel Axtens [this message]
2021-06-17  7:06   ` [PATCH v14 1/4] kasan: allow an architecture to disable inline instrumentation Marco Elver
2021-06-17  6:39 ` [PATCH v14 2/4] kasan: allow architectures to provide an outline readiness check Daniel Axtens
2021-06-17  6:55   ` Christophe Leroy
2021-06-17  6:59   ` Christophe Leroy
2021-06-17  7:06   ` Marco Elver
2021-06-17  6:39 ` [PATCH v14 3/4] mm: define default MAX_PTRS_PER_* in include/pgtable.h Daniel Axtens
2021-06-17  7:00   ` Christophe Leroy
2021-06-17  7:08   ` Marco Elver
2021-06-17  6:39 ` [PATCH v14 4/4] kasan: use MAX_PTRS_PER_* for early shadow tables Daniel Axtens
2021-06-17  7:09   ` Marco Elver

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