Re: [Qemu-devel] [PATCH 5/6] hw/timer/armv7m_systick: Forbid non-privileged accesses

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 6/17/19 7:53 PM, Peter Maydell wrote:
> Like most of the v7M memory mapped system registers, the systick
> registers are accessible to privileged code only and user accesses
> must generate a BusFault. We implement that for registers in
> the NVIC proper already, but missed it for systick since we
> implement it as a separate device. Correct the omission.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/timer/armv7m_systick.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/timer/armv7m_systick.c b/hw/timer/armv7m_systick.c
> index a17317ce2fe..94640743b5d 100644
> --- a/hw/timer/armv7m_systick.c
> +++ b/hw/timer/armv7m_systick.c
> @@ -75,11 +75,17 @@ static void systick_timer_tick(void *opaque)
>      }
>  }
>  
> -static uint64_t systick_read(void *opaque, hwaddr addr, unsigned size)
> +static MemTxResult systick_read(void *opaque, hwaddr addr, uint64_t *data,
> +                                unsigned size, MemTxAttrs attrs)
>  {
>      SysTickState *s = opaque;
>      uint32_t val;
>  
> +    if (attrs.user) {
> +        /* Generate BusFault for unprivileged accesses */
> +        return MEMTX_ERROR;
> +    }
> +
>      switch (addr) {
>      case 0x0: /* SysTick Control and Status.  */
>          val = s->control;
> @@ -121,14 +127,21 @@ static uint64_t systick_read(void *opaque, hwaddr addr, unsigned size)
>      }
>  
>      trace_systick_read(addr, val, size);
> -    return val;
> +    *data = val;
> +    return MEMTX_OK;
>  }
>  
> -static void systick_write(void *opaque, hwaddr addr,
> -                          uint64_t value, unsigned size)
> +static MemTxResult systick_write(void *opaque, hwaddr addr,
> +                                 uint64_t value, unsigned size,
> +                                 MemTxAttrs attrs)
>  {
>      SysTickState *s = opaque;
>  
> +    if (attrs.user) {
> +        /* Generate BusFault for unprivileged accesses */
> +        return MEMTX_ERROR;
> +    }
> +
>      trace_systick_write(addr, value, size);
>  
>      switch (addr) {
> @@ -172,11 +185,12 @@ static void systick_write(void *opaque, hwaddr addr,
>          qemu_log_mask(LOG_GUEST_ERROR,
>                        "SysTick: Bad write offset 0x%" HWADDR_PRIx "\n", addr);
>      }
> +    return MEMTX_OK;
>  }
>  
>  static const MemoryRegionOps systick_ops = {
> -    .read = systick_read,
> -    .write = systick_write,
> +    .read_with_attrs = systick_read,
> +    .write_with_attrs = systick_write,
>      .endianness = DEVICE_NATIVE_ENDIAN,
>      .valid.min_access_size = 4,
>      .valid.max_access_size = 4,
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>