Re: [PATCH mm v10 23/42] kasan: introduce CONFIG_KASAN_HW_TAGS

[Alexander Potapenko]

On Fri, Nov 13, 2020 at 11:17 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> This patch adds a configuration option for a new KASAN mode called
> hardware tag-based KASAN. This mode uses the memory tagging approach
> like the software tag-based mode, but relies on arm64 Memory Tagging
> Extension feature for tag management and access checking.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Co-developed-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>

> ---
> Change-Id: I246c2def9fffa6563278db1bddfbe742ca7bdefe
> ---
>  lib/Kconfig.kasan | 61 ++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 44 insertions(+), 17 deletions(-)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index c0e9e7874122..f5fa4ba126bf 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -6,7 +6,10 @@ config HAVE_ARCH_KASAN
>  config HAVE_ARCH_KASAN_SW_TAGS
>         bool
>
> -config HAVE_ARCH_KASAN_VMALLOC
> +config HAVE_ARCH_KASAN_HW_TAGS
> +       bool
> +
> +config HAVE_ARCH_KASAN_VMALLOC
>         bool
>
>  config CC_HAS_KASAN_GENERIC
> @@ -15,16 +18,19 @@ config CC_HAS_KASAN_GENERIC
>  config CC_HAS_KASAN_SW_TAGS
>         def_bool $(cc-option, -fsanitize=kernel-hwaddress)
>
> +# This option is only required for software KASAN modes.
> +# Old GCC versions don't have proper support for no_sanitize_address.
> +# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89124 for details.
>  config CC_HAS_WORKING_NOSANITIZE_ADDRESS
>         def_bool !CC_IS_GCC || GCC_VERSION >= 80300
>
>  menuconfig KASAN
>         bool "KASAN: runtime memory debugger"
> -       depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
> -                  (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
> +       depends on (((HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
> +                    (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
> +                   CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
> +                  HAVE_ARCH_KASAN_HW_TAGS
>         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
> -       depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
> -       select CONSTRUCTORS
>         select STACKDEPOT
>         help
>           Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
> @@ -37,18 +43,24 @@ choice
>         prompt "KASAN mode"
>         default KASAN_GENERIC
>         help
> -         KASAN has two modes: generic KASAN (similar to userspace ASan,
> -         x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
> -         software tag-based KASAN (a version based on software memory
> -         tagging, arm64 only, similar to userspace HWASan, enabled with
> -         CONFIG_KASAN_SW_TAGS).
> +         KASAN has three modes:
> +         1. generic KASAN (similar to userspace ASan,
> +            x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC),
> +         2. software tag-based KASAN (arm64 only, based on software
> +            memory tagging (similar to userspace HWASan), enabled with
> +            CONFIG_KASAN_SW_TAGS), and
> +         3. hardware tag-based KASAN (arm64 only, based on hardware
> +            memory tagging, enabled with CONFIG_KASAN_HW_TAGS).
> +
> +         All KASAN modes are strictly debugging features.
>
> -         Both generic and tag-based KASAN are strictly debugging features.
> +         For better error reports enable CONFIG_STACKTRACE.
>
>  config KASAN_GENERIC
>         bool "Generic mode"
>         depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
>         select SLUB_DEBUG if SLUB
> +       select CONSTRUCTORS
>         help
>           Enables generic KASAN mode.
>
> @@ -61,8 +73,6 @@ config KASAN_GENERIC
>           and introduces an overhead of ~x1.5 for the rest of the allocations.
>           The performance slowdown is ~x3.
>
> -         For better error detection enable CONFIG_STACKTRACE.
> -
>           Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
>           (the resulting kernel does not boot).
>
> @@ -70,11 +80,15 @@ config KASAN_SW_TAGS
>         bool "Software tag-based mode"
>         depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
>         select SLUB_DEBUG if SLUB
> +       select CONSTRUCTORS
>         help
>           Enables software tag-based KASAN mode.
>
> -         This mode requires Top Byte Ignore support by the CPU and therefore
> -         is only supported for arm64. This mode requires Clang.
> +         This mode require software memory tagging support in the form of
> +         HWASan-like compiler instrumentation.
> +
> +         Currently this mode is only implemented for arm64 CPUs and relies on
> +         Top Byte Ignore. This mode requires Clang.
>
>           This mode consumes about 1/16th of available memory at kernel start
>           and introduces an overhead of ~20% for the rest of the allocations.
> @@ -82,15 +96,27 @@ config KASAN_SW_TAGS
>           casting and comparison, as it embeds tags into the top byte of each
>           pointer.
>
> -         For better error detection enable CONFIG_STACKTRACE.
> -
>           Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
>           (the resulting kernel does not boot).
>
> +config KASAN_HW_TAGS
> +       bool "Hardware tag-based mode"
> +       depends on HAVE_ARCH_KASAN_HW_TAGS
> +       depends on SLUB
> +       help
> +         Enables hardware tag-based KASAN mode.
> +
> +         This mode requires hardware memory tagging support, and can be used
> +         by any architecture that provides it.
> +
> +         Currently this mode is only implemented for arm64 CPUs starting from
> +         ARMv8.5 and relies on Memory Tagging Extension and Top Byte Ignore.
> +
>  endchoice
>
>  choice
>         prompt "Instrumentation type"
> +       depends on KASAN_GENERIC || KASAN_SW_TAGS
>         default KASAN_OUTLINE
>
>  config KASAN_OUTLINE
> @@ -114,6 +140,7 @@ endchoice
>
>  config KASAN_STACK_ENABLE
>         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
> +       depends on KASAN_GENERIC || KASAN_SW_TAGS
>         help
>           The LLVM stack address sanitizer has a know problem that
>           causes excessive stack usage in a lot of functions, see
> --
> 2.29.2.299.gdc1121823c-goog
>


-- 
Alexander Potapenko
Software Engineer

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