hw/nvme: fix CVE-2021-3929

This fixes CVE-2021-3929 "locally" by denying DMA to the iomem of the
device itself. This still allows DMA to MMIO regions of other devices
(e.g. doing P2P DMA to the controller memory buffer of another NVMe
device).

Fixes: CVE-2021-3929
Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>

hw/nvme/ctrl.c

@@ -357,6 +357,24 @@ static inline void *nvme_addr_to_pmr(NvmeCtrl *n, hwaddr addr)
     return memory_region_get_ram_ptr(&n->pmr.dev->mr) + (addr - n->pmr.cba);
 }
 
+static inline bool nvme_addr_is_iomem(NvmeCtrl *n, hwaddr addr)
+{
+    hwaddr hi, lo;
+
+    /*
+     * The purpose of this check is to guard against invalid "local" access to
+     * the iomem (i.e. controller registers). Thus, we check against the range
+     * covered by the 'bar0' MemoryRegion since that is currently composed of
+     * two subregions (the NVMe "MBAR" and the MSI-X table/pba). Note, however,
+     * that if the device model is ever changed to allow the CMB to be located
+     * in BAR0 as well, then this must be changed.
+     */
+    lo = n->bar0.addr;
+    hi = lo + int128_get64(n->bar0.size);
+
+    return addr >= lo && addr < hi;
+}
+
 static int nvme_addr_read(NvmeCtrl *n, hwaddr addr, void *buf, int size)
 {
     hwaddr hi = addr + size - 1;
@@ -614,6 +632,10 @@ static uint16_t nvme_map_addr(NvmeCtrl *n, NvmeSg *sg, hwaddr addr, size_t len)
 
     trace_pci_nvme_map_addr(addr, len);
 
+    if (nvme_addr_is_iomem(n, addr)) {
+        return NVME_DATA_TRAS_ERROR;
+    }
+
     if (nvme_addr_is_cmb(n, addr)) {
         cmb = true;
     } else if (nvme_addr_is_pmr(n, addr)) {