hw/timer/armv7m_systick: Forbid non-privileged accesses

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>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190617175317.27557-6-peter.maydell@linaro.org

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,