Re: [PATCH 10/17] arm64: Add CNTVCT_EL0 trap handler

[Mark Rutland]

On Mon, Mar 06, 2017 at 11:26:15AM +0000, Marc Zyngier wrote:
> Since people seem to make a point in breaking the userspace visible
> counter, we have no choice but to trap the access. Add the required
> handler.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  arch/arm64/include/asm/esr.h |  2 ++
>  arch/arm64/kernel/traps.c    | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index d14c478976d0..ad42e79a5d4d 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -175,6 +175,8 @@
>  #define ESR_ELx_SYS64_ISS_SYS_CTR_READ	(ESR_ELx_SYS64_ISS_SYS_CTR | \
>  					 ESR_ELx_SYS64_ISS_DIR_READ)
>  
> +#define ESR_ELx_SYS64_ISS_SYS_CNTVCT	(ESR_ELx_SYS64_ISS_SYS_VAL(3, 3, 2, 14, 0) | \
> +					 ESR_ELx_SYS64_ISS_DIR_READ)
>  #ifndef __ASSEMBLY__
>  #include <asm/types.h>
>  
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index e52be6aa44ee..1de444e6c669 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -505,6 +505,14 @@ static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
>  	regs->pc += 4;
>  }
>  
> +static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
> +{
> +	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
> +
> +	pt_regs_write_reg(regs, rt, arch_counter_get_cntvct());
> +	regs->pc += 4;
> +}

I was going to suggest it'd be worth using AARCH64_INSN_SIZE, but I see
most of the other handlers in this file don't, so I guess that's not a
big deal.

Otherwise, this looks fine to me. FWIW:

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> +
>  struct sys64_hook {
>  	unsigned int esr_mask;
>  	unsigned int esr_val;
> @@ -523,6 +531,12 @@ static struct sys64_hook sys64_hooks[] = {
>  		.esr_val = ESR_ELx_SYS64_ISS_SYS_CTR_READ,
>  		.handler = ctr_read_handler,
>  	},
> +	{
> +		/* Trap read access to CNTVCT_EL0 */
> +		.esr_mask = ESR_ELx_SYS64_ISS_SYS_OP_MASK,
> +		.esr_val = ESR_ELx_SYS64_ISS_SYS_CNTVCT,
> +		.handler = cntvct_read_handler,
> +	},
>  	{},
>  };
>  
> -- 
> 2.11.0
>