[RFC PATCH v3 3/3] softmmu/physmem: Introduce MemTxAttrs::memory field and MEMTX_BUS_ERROR

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

Add the 'memory' bit to the memory attributes to restrict bus
controller accesses to memories.

Introduce flatview_access_allowed() to check bus permission
before running any bus transaction.

Have read/write accessors return MEMTX_BUS_ERROR if an access is
restricted.

There is no change for the default case where 'memory' is not set.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 include/exec/memattrs.h |  9 +++++++++
 softmmu/physmem.c       | 43 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/include/exec/memattrs.h b/include/exec/memattrs.h
index 95f2d20d55b..f0063583ee2 100644
--- a/include/exec/memattrs.h
+++ b/include/exec/memattrs.h
@@ -35,6 +35,14 @@ typedef struct MemTxAttrs {
     unsigned int secure:1;
     /* Memory access is usermode (unprivileged) */
     unsigned int user:1;
+    /*
+     * Bus interconnect and peripherals can access anything (memories,
+     * devices) by default. By setting the 'memory' bit, bus transaction
+     * are restricted to "normal" memories (per the AMBA documentation)
+     * versus devices. Access to devices will be logged and rejected
+     * (see MEMTX_BUS_ERROR).
+     */
+    unsigned int memory:1;
     /* Requester ID (for MSI for example) */
     unsigned int requester_id:16;
     /* Invert endianness for this page */
@@ -66,6 +74,7 @@ typedef struct MemTxAttrs {
 #define MEMTX_OK 0
 #define MEMTX_ERROR             (1U << 0) /* device returned an error */
 #define MEMTX_DECODE_ERROR      (1U << 1) /* nothing at that address */
+#define MEMTX_BUS_ERROR         (1U << 2) /* bus returned an error */
 typedef uint32_t MemTxResult;
 
 #endif
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 6c97a20107a..c03abcc0362 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -2759,6 +2759,33 @@ static bool prepare_mmio_access(MemoryRegion *mr)
     return release_lock;
 }
 
+/**
+ * flatview_access_allowed
+ * @mr: #MemoryRegion to be accessed
+ * @attrs: memory transaction attributes
+ * @addr: address within that memory region
+ * @len: the number of bytes to access
+ *
+ * Check if a memory transaction is allowed.
+ *
+ * Returns: true if transaction is allowed, false if denied.
+ */
+static inline bool flatview_access_allowed(MemoryRegion *mr, MemTxAttrs attrs,
+                                           hwaddr addr, hwaddr len)
+{
+    if (likely(!attrs.memory)) {
+        return true;
+    }
+    if (memory_region_is_ram(mr)) {
+        return true;
+    }
+    qemu_log_mask(LOG_GUEST_ERROR,
+                  "Invalid access to non-RAM device at "
+                  "addr 0x%" HWADDR_PRIX ", size %" HWADDR_PRIu ", "
+                  "region '%s'\n", addr, len, memory_region_name(mr));
+    return false;
+}
+
 /* Called within RCU critical section.  */
 static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
                                            MemTxAttrs attrs,
@@ -2773,7 +2800,10 @@ static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
     const uint8_t *buf = ptr;
 
     for (;;) {
-        if (!memory_access_is_direct(mr, true)) {
+        if (!flatview_access_allowed(mr, attrs, addr1, l)) {
+            result |= MEMTX_BUS_ERROR;
+            /* Keep going. */
+        } else if (!memory_access_is_direct(mr, true)) {
             release_lock |= prepare_mmio_access(mr);
             l = memory_access_size(mr, l, addr1);
             /* XXX: could force current_cpu to NULL to avoid
@@ -2818,6 +2848,9 @@ static MemTxResult flatview_write(FlatView *fv, hwaddr addr, MemTxAttrs attrs,
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, true, attrs);
+    if (!flatview_access_allowed(mr, attrs, addr, len)) {
+        return MEMTX_BUS_ERROR;
+    }
     return flatview_write_continue(fv, addr, attrs, buf, len,
                                    addr1, l, mr);
 }
@@ -2836,7 +2869,10 @@ MemTxResult flatview_read_continue(FlatView *fv, hwaddr addr,
 
     fuzz_dma_read_cb(addr, len, mr);
     for (;;) {
-        if (!memory_access_is_direct(mr, false)) {
+        if (!flatview_access_allowed(mr, attrs, addr1, l)) {
+            result |= MEMTX_BUS_ERROR;
+            /* Keep going. */
+        } else if (!memory_access_is_direct(mr, false)) {
             /* I/O case */
             release_lock |= prepare_mmio_access(mr);
             l = memory_access_size(mr, l, addr1);
@@ -2879,6 +2915,9 @@ static MemTxResult flatview_read(FlatView *fv, hwaddr addr,
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, false, attrs);
+    if (!flatview_access_allowed(mr, attrs, addr, len)) {
+        return MEMTX_BUS_ERROR;
+    }
     return flatview_read_continue(fv, addr, attrs, buf, len,
                                   addr1, l, mr);
 }
-- 
2.33.1