[PATCH v2 2/4] arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

[Mark Rutland]

On Wed, May 03, 2017 at 04:37:46PM +0100, Kristina Martsenko wrote:
> When we take a watchpoint exception, the address that triggered the
> watchpoint is found in FAR_EL1. We compare it to the address of each
> configured watchpoint to see which one was hit.
> 
> The configured watchpoint addresses are untagged, while the address in
> FAR_EL1 will have an address tag if the data access was done using a
> tagged address. The tag needs to be removed to compare the address to
> the watchpoints.
> 
> Currently we don't remove it, and as a result can report the wrong
> watchpoint as being hit (specifically, always either the highest TTBR0
> watchpoint or lowest TTBR1 watchpoint). This patch removes the tag.
> 
> Fixes: d50240a5f6ce ("arm64: mm: permit use of tagged pointers at EL0")
> Signed-off-by: Kristina Martsenko <kristina.martsenko at arm.com>

Looks sane to me. FWIW:

Acked-by: Mark Rutland <mark.rutland at arm.com>

Mark.

> ---
>  arch/arm64/include/asm/uaccess.h  | 6 +++---
>  arch/arm64/kernel/hw_breakpoint.c | 3 +++
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 5308d696311b..0221029e27ff 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -106,9 +106,9 @@ static inline void set_fs(mm_segment_t fs)
>  })
>  
>  /*
> - * When dealing with data aborts or instruction traps we may end up with
> - * a tagged userland pointer. Clear the tag to get a sane pointer to pass
> - * on to access_ok(), for instance.
> + * When dealing with data aborts, watchpoints, or instruction traps we may end
> + * up with a tagged userland pointer. Clear the tag to get a sane pointer to
> + * pass on to access_ok(), for instance.
>   */
>  #define untagged_addr(addr)		sign_extend64(addr, 55)
>  
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index 0296e7924240..749f81779420 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -36,6 +36,7 @@
>  #include <asm/traps.h>
>  #include <asm/cputype.h>
>  #include <asm/system_misc.h>
> +#include <asm/uaccess.h>
>  
>  /* Breakpoint currently in use for each BRP. */
>  static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
> @@ -721,6 +722,8 @@ static u64 get_distance_from_watchpoint(unsigned long addr, u64 val,
>  	u64 wp_low, wp_high;
>  	u32 lens, lene;
>  
> +	addr = untagged_addr(addr);
> +
>  	lens = __ffs(ctrl->len);
>  	lene = __fls(ctrl->len);
>  
> -- 
> 2.1.4
>