Re: [PATCH RFC v2 13/21] arm64: kasan: Add cpu_supports_tags helper

[Dmitry Vyukov]

On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> Add an arm64 helper called cpu_supports_mte() that exposes information
> about whether the CPU supports memory tagging and that can be called
> during early boot (unlike system_supports_mte()).
>
> Use that helper to implement a generic cpu_supports_tags() helper, that
> will be used by hardware tag-based KASAN.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/Ib4b56a42c57c6293df29a0cdfee334c3ca7bdab4

Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

> ---
>  arch/arm64/include/asm/memory.h    |  1 +
>  arch/arm64/include/asm/mte-kasan.h |  6 ++++++
>  arch/arm64/kernel/mte.c            | 20 ++++++++++++++++++++
>  mm/kasan/kasan.h                   |  4 ++++
>  4 files changed, 31 insertions(+)
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index b5d6b824c21c..f496abfcf7f5 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -232,6 +232,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
>  }
>
>  #ifdef CONFIG_KASAN_HW_TAGS
> +#define arch_cpu_supports_tags()               cpu_supports_mte()
>  #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 a4c61b926d4a..4c3f2c6b4fe6 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/init.h>
>  #include <linux/types.h>
>
>  /*
> @@ -30,6 +31,7 @@ u8 mte_get_random_tag(void);
>  void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
>
>  void mte_init_tags(u64 max_tag);
> +bool __init cpu_supports_mte(void);
>
>  #else /* CONFIG_ARM64_MTE */
>
> @@ -54,6 +56,10 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
>  static inline void mte_init_tags(u64 max_tag)
>  {
>  }
> +static inline bool cpu_supports_mte(void)
> +{
> +       return false;
> +}
>
>  #endif /* CONFIG_ARM64_MTE */
>
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index ca8206b7f9a6..8fcd17408515 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -134,6 +134,26 @@ void mte_init_tags(u64 max_tag)
>         gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
>  }
>
> +/*
> + * This function can be used during early boot to determine whether the CPU
> + * supports MTE. The alternative that must be used after boot is completed is
> + * system_supports_mte(), but it only works after the cpufeature framework
> + * learns about MTE.
> + */
> +bool __init cpu_supports_mte(void)
> +{
> +       u64 pfr1;
> +       u32 val;
> +
> +       if (!IS_ENABLED(CONFIG_ARM64_MTE))
> +               return false;
> +
> +       pfr1 = read_cpuid(ID_AA64PFR1_EL1);
> +       val = cpuid_feature_extract_unsigned_field(pfr1, ID_AA64PFR1_MTE_SHIFT);
> +
> +       return val >= ID_AA64PFR1_MTE;
> +}
> +
>  static void update_sctlr_el1_tcf0(u64 tcf0)
>  {
>         /* ISB required for the kernel uaccess routines */
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index da08b2533d73..f7ae0c23f023 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -240,6 +240,9 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  #define set_tag(addr, tag)     ((void *)arch_kasan_set_tag((addr), (tag)))
>  #define get_tag(addr)          arch_kasan_get_tag(addr)
>
> +#ifndef arch_cpu_supports_tags
> +#define arch_cpu_supports_tags() (false)
> +#endif
>  #ifndef arch_init_tags
>  #define arch_init_tags(max_tag)
>  #endif
> @@ -253,6 +256,7 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  #define arch_set_mem_tag_range(addr, size, tag) ((void *)(addr))
>  #endif
>
> +#define cpu_supports_tags()                    arch_cpu_supports_tags()
>  #define init_tags(max_tag)                     arch_init_tags(max_tag)
>  #define get_random_tag()                       arch_get_random_tag()
>  #define get_mem_tag(addr)                      arch_get_mem_tag(addr)
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>