Re: [PATCH v3 22/39] kasan: introduce CONFIG_KASAN_HW_TAGS

elver
2020-10-01T17:57:29Z

On Fri, Sep 25, 2020 at 12:50AM +0200, Andrey Konovalov 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@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

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

> ---
> Change-Id: I246c2def9fffa6563278db1bddfbe742ca7bdefe
> ---
> lib/Kconfig.kasan | 59 ++++++++++++++++++++++++++++++++---------------
> 1 file changed, 41 insertions(+), 18 deletions(-)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index b4cf6c519d71..516d3a24f7d7 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
> @@ -20,11 +23,11 @@ config CC_HAS_WORKING_NOSANITIZE_ADDRESS
>
> 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 SLUB_DEBUG if SLUB

See my comment in the other patch about moving this line again.

> select CONSTRUCTORS
> select STACKDEPOT
> help
> @@ -38,17 +41,23 @@ 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
> help
> Enables generic KASAN mode.
>
> @@ -61,20 +70,21 @@ 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).
>
> 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
> 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 version 7.0.0
> - or later.
> + 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 version 7.0.0 or later.
>
> 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 +92,27 @@ 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 +136,7 @@ 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
> --
> 2.28.0.681.g6f77f65b4e-goog
>