Re: [PATCH v3 1/4] kasan, arm64: Add KASAN light mode

[Andrey Konovalov]

On Fri, Jan 15, 2021 at 1:00 PM Vincenzo Frascino
<vincenzo.frascino@xxxxxxx> wrote:
>
> Architectures supported by KASAN HW can provide a light mode of
> execution. On an MTE enabled arm64 hw for example this can be identified
> with the asynch mode of execution.
> In this mode, if a tag check fault occurs, the TFSR_EL1 register is
> updated asynchronously. The kernel checks the corresponding bits
> periodically.
>
> KASAN requires a specific mode of execution to make use of this hw feature.
>
> Add KASAN HW light execution mode.
>
> Note: This patch adds the KASAN_ARG_MODE_LIGHT config option and the
> "light" kernel command line option to enable the described feature.
> This patch introduces the kasan_def.h header to make easier to propagate
> the relevant enumerations to the architectural code.
>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> ---
>  arch/arm64/include/asm/memory.h    |  2 +-
>  arch/arm64/include/asm/mte-kasan.h |  5 +++--
>  arch/arm64/kernel/mte.c            |  2 +-
>  include/linux/kasan.h              |  1 +
>  include/linux/kasan_def.h          | 10 ++++++++++
>  mm/kasan/hw_tags.c                 | 19 ++++++++++++++++++-
>  mm/kasan/kasan.h                   |  2 +-
>  7 files changed, 35 insertions(+), 6 deletions(-)
>  create mode 100644 include/linux/kasan_def.h
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 18fce223b67b..3a7c5beb7096 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -231,7 +231,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
>  }
>
>  #ifdef CONFIG_KASAN_HW_TAGS
> -#define arch_enable_tagging()                  mte_enable_kernel()
> +#define arch_enable_tagging(mode)              mte_enable_kernel(mode)
>  #define arch_init_tags(max_tag)                        mte_init_tags(max_tag)
>  #define arch_get_random_tag()                  mte_get_random_tag()
>  #define arch_get_mem_tag(addr)                 mte_get_mem_tag(addr)
> diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
> index 26349a4b5e2e..5402f4c8e88d 100644
> --- a/arch/arm64/include/asm/mte-kasan.h
> +++ b/arch/arm64/include/asm/mte-kasan.h
> @@ -9,6 +9,7 @@
>
>  #ifndef __ASSEMBLY__
>
> +#include <linux/kasan_def.h>
>  #include <linux/types.h>
>
>  /*
> @@ -29,7 +30,7 @@ u8 mte_get_mem_tag(void *addr);
>  u8 mte_get_random_tag(void);
>  void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
>
> -void mte_enable_kernel(void);
> +void mte_enable_kernel(enum kasan_hw_tags_mode mode);
>  void mte_init_tags(u64 max_tag);
>
>  #else /* CONFIG_ARM64_MTE */
> @@ -52,7 +53,7 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
>         return addr;
>  }
>
> -static inline void mte_enable_kernel(void)
> +static inline void mte_enable_kernel(enum kasan_hw_tags_mode mode)
>  {
>  }
>
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index dc9ada64feed..53a6d734e29b 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -151,7 +151,7 @@ void mte_init_tags(u64 max_tag)
>         write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
>  }
>
> -void mte_enable_kernel(void)
> +void mte_enable_kernel(enum kasan_hw_tags_mode mode)
>  {
>         /* Enable MTE Sync Mode for EL1. */
>         sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 5e0655fb2a6f..026031444217 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -2,6 +2,7 @@
>  #ifndef _LINUX_KASAN_H
>  #define _LINUX_KASAN_H
>
> +#include <linux/kasan_def.h>
>  #include <linux/static_key.h>
>  #include <linux/types.h>
>
> diff --git a/include/linux/kasan_def.h b/include/linux/kasan_def.h
> new file mode 100644
> index 000000000000..0a55400809c9
> --- /dev/null
> +++ b/include/linux/kasan_def.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_KASAN_DEF_H
> +#define _LINUX_KASAN_DEF_H
> +
> +enum kasan_hw_tags_mode {
> +       KASAN_HW_TAGS_SYNC,
> +       KASAN_HW_TAGS_ASYNC,
> +};
> +
> +#endif /* _LINUX_KASAN_DEF_H */
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 55bd6f09c70f..6c3b0742f639 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -22,6 +22,7 @@
>  enum kasan_arg_mode {
>         KASAN_ARG_MODE_DEFAULT,
>         KASAN_ARG_MODE_OFF,
> +       KASAN_ARG_MODE_LIGHT,
>         KASAN_ARG_MODE_PROD,
>         KASAN_ARG_MODE_FULL,
>  };
> @@ -60,6 +61,8 @@ static int __init early_kasan_mode(char *arg)
>
>         if (!strcmp(arg, "off"))
>                 kasan_arg_mode = KASAN_ARG_MODE_OFF;
> +       else if (!strcmp(arg, "light"))
> +               kasan_arg_mode = KASAN_ARG_MODE_LIGHT;

Hi Vincenzo,

I've just mailed the change to KASAN parameters [1] as discussed, so
we should use a standalone parameter here (kasan.trap?).

Thanks!

[1] https://lkml.org/lkml/2021/1/15/1242