[PATCH 1/2] kasan: arm64: set TCR_EL1.TBID1 when enabled

[Andrey Konovalov]

On Sat, Nov 21, 2020 at 10:59 AM Peter Collingbourne <pcc at google.com> wrote:
>
> On hardware supporting pointer authentication, we previously ended up
> enabling TBI on instruction accesses when tag-based ASAN was enabled,
> but this was costing us 8 bits of PAC entropy, which was unnecessary
> since tag-based ASAN does not require TBI on instruction accesses. Get
> them back by setting TCR_EL1.TBID1.
>
> Signed-off-by: Peter Collingbourne <pcc at google.com>
> Link: https://linux-review.googlesource.com/id/I3dded7824be2e70ea64df0aabab9598d5aebfcc4
> ---
>  arch/arm64/include/asm/pgtable-hwdef.h | 1 +
>  arch/arm64/mm/proc.S                   | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index 01a96d07ae74..42442a0ae2ab 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -260,6 +260,7 @@
>  #define TCR_TBI1               (UL(1) << 38)
>  #define TCR_HA                 (UL(1) << 39)
>  #define TCR_HD                 (UL(1) << 40)
> +#define TCR_TBID1              (UL(1) << 52)
>  #define TCR_NFD0               (UL(1) << 53)
>  #define TCR_NFD1               (UL(1) << 54)
>  #define TCR_E0PD0              (UL(1) << 55)
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 23c326a06b2d..97a97a61a8dc 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -40,7 +40,7 @@
>  #define TCR_CACHE_FLAGS        TCR_IRGN_WBWA | TCR_ORGN_WBWA
>
>  #ifdef CONFIG_KASAN_SW_TAGS
> -#define TCR_KASAN_FLAGS TCR_TBI1
> +#define TCR_KASAN_FLAGS TCR_TBI1 | TCR_TBID1
>  #else
>  #define TCR_KASAN_FLAGS 0
>  #endif
> --
> 2.29.2.454.gaff20da3a2-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl at google.com>