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SubjectRe: [PATCH 10/17] arm64: Add CNTVCT_EL0 trap handler
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@arm.com>
> ---
> 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@arm.com>

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
>

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