diff mbox series

[v15,1/4] kasan: allow an architecture to disable inline instrumentation

Message ID 20210617093032.103097-2-dja@axtens.net (mailing list archive)
State New
Headers show
Series KASAN core changes for ppc64 radix KASAN | expand

Commit Message

Daniel Axtens June 17, 2021, 9:30 a.m. UTC
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.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 lib/Kconfig.kasan | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Comments

Andrey Konovalov June 20, 2021, 11:15 a.m. UTC | #1
On Thu, Jun 17, 2021 at 12:30 PM Daniel Axtens <dja@axtens.net> wrote:
>
> 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.
>
> Reviewed-by: Marco Elver <elver@google.com>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> ---
>  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
>  config HAVE_ARCH_KASAN_VMALLOC
>         bool
>
> +config ARCH_DISABLE_KASAN_INLINE
> +       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.

This seems too wordy.

How about: "An architecture might not support inline instrumentation.
When this option is selected, inline and stack instrumentation are
disabled."

> +
> +

Drop the extra empty line.

>  config CC_HAS_KASAN_GENERIC
>         def_bool $(cc-option, -fsanitize=kernel-address)
>
> @@ -130,6 +139,7 @@ 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
> @@ -141,6 +151,7 @@ endchoice
>  config KASAN_STACK
>         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
>         depends on KASAN_GENERIC || KASAN_SW_TAGS
> +       depends on !ARCH_DISABLE_KASAN_INLINE
>         default y if CC_IS_GCC
>         help
>           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

this => stack instrumentation



> +         also disabled as it adds inline-style instrumentation that
> +         is run unconditionally.
>
>  config KASAN_SW_TAGS_IDENTIFY
>         bool "Enable memory corruption identification"
> --
> 2.30.2
>
diff mbox series

Patch

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
 config HAVE_ARCH_KASAN_VMALLOC
 	bool
 
+config ARCH_DISABLE_KASAN_INLINE
+	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.
+
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
@@ -130,6 +139,7 @@  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
@@ -141,6 +151,7 @@  endchoice
 config KASAN_STACK
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 	depends on KASAN_GENERIC || KASAN_SW_TAGS
+	depends on !ARCH_DISABLE_KASAN_INLINE
 	default y if CC_IS_GCC
 	help
 	  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.
 
 config KASAN_SW_TAGS_IDENTIFY
 	bool "Enable memory corruption identification"