libvhost-user: Mark mmap'ed region memory as MADV_DONTDUMP

We already use MADV_NORESERVE to deal with sparse memory regions. Let's
also set madvise(MADV_DONTDUMP), otherwise a crash of the process can
result in us allocating all memory in the mmap'ed region for dumping
purposes.

This change implies that the mmap'ed rings won't be included in a
coredump. If ever required for debugging purposes, we could mark only
the mapped rings MADV_DODUMP.

Ignore errors during madvise() for now.

Reviewed-by: Raphael Norwitz <raphael@enfabrica.net>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20240214151701.29906-15-david@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -460,6 +460,12 @@ _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion *msg_region, int fd)
     DPRINT("    mmap_addr:       0x%016"PRIx64"\n",
            (uint64_t)(uintptr_t)mmap_addr);
 
+#if defined(__linux__)
+    /* Don't include all guest memory in a coredump. */
+    madvise(mmap_addr, msg_region->memory_size + mmap_offset,
+            MADV_DONTDUMP);
+#endif
+
     /* Shift all affected entries by 1 to open a hole at idx. */
     r = &dev->regions[idx];
     memmove(r + 1, r, sizeof(VuDevRegion) * (dev->nregions - idx));