[Qemu-devel] [PATCH v3 2/5] kvm: support using KVM_MEM_READONLY flag for readonly regions

[Jordan Justen <jordan.l.justen@intel.com>]

A slot that uses KVM_MEM_READONLY can be read from and code
can execute from the region, but writes will trap.

For regions that are readonly and also not writeable, we
force the slot to be removed so reads or writes to the region
will trap. (A memory region in this state is not executable
within kvm.)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
 kvm-all.c |   36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index 1686adc..fffd2f4 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -201,12 +201,18 @@ static int kvm_set_user_memory_region(KVMState *s, KVMSlot *slot)
 
     mem.slot = slot->slot;
     mem.guest_phys_addr = slot->start_addr;
-    mem.memory_size = slot->memory_size;
     mem.userspace_addr = (unsigned long)slot->ram;
     mem.flags = slot->flags;
     if (s->migration_log) {
         mem.flags |= KVM_MEM_LOG_DIRTY_PAGES;
     }
+    if (mem.flags & KVM_MEM_READONLY && mem.memory_size != 0) {
+        /* Set the slot size to 0 before setting the slot to the desired
+         * value. This is needed based on KVM commit 75d61fbc. */
+        mem.memory_size = 0;
+        kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+    }
+    mem.memory_size = slot->memory_size;
     return kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
 }
 
@@ -268,9 +274,14 @@ err:
  * dirty pages logging control
  */
 
-static int kvm_mem_flags(KVMState *s, bool log_dirty)
+static int kvm_mem_flags(KVMState *s, bool log_dirty, bool readonly)
 {
-    return log_dirty ? KVM_MEM_LOG_DIRTY_PAGES : 0;
+    int flags = 0;
+    flags = log_dirty ? KVM_MEM_LOG_DIRTY_PAGES : 0;
+    if (readonly && kvm_readonly_mem_allowed) {
+        flags |= KVM_MEM_READONLY;
+    }
+    return flags;
 }
 
 static int kvm_slot_dirty_pages_log_change(KVMSlot *mem, bool log_dirty)
@@ -281,7 +292,7 @@ static int kvm_slot_dirty_pages_log_change(KVMSlot *mem, bool log_dirty)
 
     old_flags = mem->flags;
 
-    flags = (mem->flags & ~mask) | kvm_mem_flags(s, log_dirty);
+    flags = (mem->flags & ~mask) | kvm_mem_flags(s, log_dirty, false);
     mem->flags = flags;
 
     /* If nothing changed effectively, no need to issue ioctl */
@@ -638,7 +649,14 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
     }
 
     if (!memory_region_is_ram(mr)) {
-        return;
+        if (!mr->readonly || !kvm_readonly_mem_allowed) {
+            return;
+        } else if (!mr->readable && add) {
+            /* If the memory range is not readable, then we actually want
+             * to remove the kvm memory slot so all accesses will trap. */
+            assert(mr->readonly && kvm_readonly_mem_allowed);
+            add = false;
+        }
     }
 
     ram = memory_region_get_ram_ptr(mr) + section->offset_within_region + delta;
@@ -687,7 +705,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             mem->memory_size = old.memory_size;
             mem->start_addr = old.start_addr;
             mem->ram = old.ram;
-            mem->flags = kvm_mem_flags(s, log_dirty);
+            mem->flags = kvm_mem_flags(s, log_dirty, mr->readonly);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -708,7 +726,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             mem->memory_size = start_addr - old.start_addr;
             mem->start_addr = old.start_addr;
             mem->ram = old.ram;
-            mem->flags =  kvm_mem_flags(s, log_dirty);
+            mem->flags =  kvm_mem_flags(s, log_dirty, mr->readonly);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -732,7 +750,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             size_delta = mem->start_addr - old.start_addr;
             mem->memory_size = old.memory_size - size_delta;
             mem->ram = old.ram + size_delta;
-            mem->flags = kvm_mem_flags(s, log_dirty);
+            mem->flags = kvm_mem_flags(s, log_dirty, mr->readonly);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -754,7 +772,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
     mem->memory_size = size;
     mem->start_addr = start_addr;
     mem->ram = ram;
-    mem->flags = kvm_mem_flags(s, log_dirty);
+    mem->flags = kvm_mem_flags(s, log_dirty, mr->readonly);
 
     err = kvm_set_user_memory_region(s, mem);
     if (err) {
-- 
1.7.10.4