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SubjectRe: [PATCH v14 1/4] kasan: allow an architecture to disable inline instrumentation
On Thu, 17 Jun 2021 at 08:40, 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.
>
> Signed-off-by: Daniel Axtens <dja@axtens.net>

Reviewed-by: Marco Elver <elver@google.com>


> ---
> 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.
> +
> +
> 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"
> --
> 2.30.2
>
> --
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