diff mbox series

[1/3] memory: add readonly support to memory_region_init_ram_from_file()

Message ID 20200804101244.1283503-2-stefanha@redhat.com
State New
Headers show
Series nvdimm: read-only file support | expand

Commit Message

Stefan Hajnoczi Aug. 4, 2020, 10:12 a.m. UTC
There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
creating a memory region from a file. This functionality is needed since
the underlying host file may not allow writing.

Add a bool readonly argument to memory_region_init_ram_from_file() and
the APIs it calls.

Extend memory_region_init_ram_from_file() rather than introducing a
memory_region_init_rom_from_file() API so that callers can easily make a
choice between read/write and read-only at runtime without calling
different APIs.

No new RAMBlock flag is introduced for read-only because it's unclear
whether RAMBlocks need to know that they are read-only. Pass a bool
readonly argument instead.

Both of these design decisions can be changed in the future. It just
seemed like the simplest approach to me.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/exec/memory.h     |  2 ++
 include/exec/ram_addr.h   |  5 +++--
 include/qemu/mmap-alloc.h |  2 ++
 backends/hostmem-file.c   |  2 +-
 exec.c                    | 18 +++++++++++-------
 softmmu/memory.c          |  7 +++++--
 util/mmap-alloc.c         | 10 ++++++----
 util/oslib-posix.c        |  2 +-
 8 files changed, 31 insertions(+), 17 deletions(-)

Comments

Philippe Mathieu-Daudé Aug. 4, 2020, 12:25 p.m. UTC | #1
Hi Stefan,

On 8/4/20 12:12 PM, Stefan Hajnoczi wrote:
> There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
> creating a memory region from a file. This functionality is needed since
> the underlying host file may not allow writing.
> 
> Add a bool readonly argument to memory_region_init_ram_from_file() and
> the APIs it calls.
> 
> Extend memory_region_init_ram_from_file() rather than introducing a
> memory_region_init_rom_from_file() API so that callers can easily make a
> choice between read/write and read-only at runtime without calling
> different APIs.

What happens if we call:

 memory_region_init_ram_from_file(mr, ..., readonly=false, ...);
 memory_region_set_readonly(mr, false);

?

> 
> No new RAMBlock flag is introduced for read-only because it's unclear
> whether RAMBlocks need to know that they are read-only. Pass a bool
> readonly argument instead.
> 
> Both of these design decisions can be changed in the future. It just
> seemed like the simplest approach to me.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/exec/memory.h     |  2 ++
>  include/exec/ram_addr.h   |  5 +++--
>  include/qemu/mmap-alloc.h |  2 ++
>  backends/hostmem-file.c   |  2 +-
>  exec.c                    | 18 +++++++++++-------
>  softmmu/memory.c          |  7 +++++--
>  util/mmap-alloc.c         | 10 ++++++----
>  util/oslib-posix.c        |  2 +-
>  8 files changed, 31 insertions(+), 17 deletions(-)
> 
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 307e527835..1ae7b31e3a 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -884,6 +884,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
>   *             - RAM_PMEM: the memory is persistent memory
>   *             Other bits are ignored now.
>   * @path: the path in which to allocate the RAM.
> + * @readonly: true to open @path for reading, false for read/write.
>   * @errp: pointer to Error*, to store an error if it happens.
>   *
>   * Note that this function does not do anything to cause the data in the
> @@ -896,6 +897,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>                                        uint64_t align,
>                                        uint32_t ram_flags,
>                                        const char *path,
> +                                      bool readonly,
>                                        Error **errp);
>  
[...]
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index af25987518..d228635bb3 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -1553,15 +1553,18 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>                                        uint64_t align,
>                                        uint32_t ram_flags,
>                                        const char *path,
> +                                      bool readonly,
>                                        Error **errp)
>  {
>      Error *err = NULL;
>      memory_region_init(mr, owner, name, size);
>      mr->ram = true;
> +    mr->readonly = readonly;
>      mr->terminates = true;
>      mr->destructor = memory_region_destructor_ram;
>      mr->align = align;
> -    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
> +    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
> +                                             readonly, &err);
>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>      if (err) {
>          mr->size = int128_zero();
> @@ -1585,7 +1588,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>      mr->destructor = memory_region_destructor_ram;
>      mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
>                                             share ? RAM_SHARED : 0,
> -                                           fd, &err);
> +                                           fd, false, &err);
>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>      if (err) {
>          mr->size = int128_zero();
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 27dcccd8ec..890fda6a35 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -85,9 +85,11 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
>  void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
> +                    bool readonly,
>                      bool shared,
>                      bool is_pmem)
>  {
> +    int prot;
>      int flags;
>      int map_sync_flags = 0;
>      int guardfd;
> @@ -146,8 +148,9 @@ void *qemu_ram_mmap(int fd,
>  
>      offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
>  
> -    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -               flags | map_sync_flags, fd, 0);
> +    prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
> +
> +    ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
>  
>      if (ptr == MAP_FAILED && map_sync_flags) {
>          if (errno == ENOTSUP) {
> @@ -171,8 +174,7 @@ void *qemu_ram_mmap(int fd,
>           * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
>           * we will remove these flags to handle compatibility.
>           */
> -        ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -                   flags, fd, 0);
> +        ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
>      }
>  
>      if (ptr == MAP_FAILED) {
[...]
Philippe Mathieu-Daudé Aug. 4, 2020, 12:26 p.m. UTC | #2
On 8/4/20 2:25 PM, Philippe Mathieu-Daudé wrote:
> Hi Stefan,
> 
> On 8/4/20 12:12 PM, Stefan Hajnoczi wrote:
>> There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
>> creating a memory region from a file. This functionality is needed since
>> the underlying host file may not allow writing.
>>
>> Add a bool readonly argument to memory_region_init_ram_from_file() and
>> the APIs it calls.
>>
>> Extend memory_region_init_ram_from_file() rather than introducing a
>> memory_region_init_rom_from_file() API so that callers can easily make a
>> choice between read/write and read-only at runtime without calling
>> different APIs.
> 
> What happens if we call:
> 
>  memory_region_init_ram_from_file(mr, ..., readonly=false, ...);
>  memory_region_set_readonly(mr, false);

In case my error is not obvious, I meant:

   memory_region_init_ram_from_file(mr, ..., readonly=true, ...);
   memory_region_set_readonly(mr, false);

> 
> ?
> 
>>
>> No new RAMBlock flag is introduced for read-only because it's unclear
>> whether RAMBlocks need to know that they are read-only. Pass a bool
>> readonly argument instead.
>>
>> Both of these design decisions can be changed in the future. It just
>> seemed like the simplest approach to me.
>>
>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>> ---
>>  include/exec/memory.h     |  2 ++
>>  include/exec/ram_addr.h   |  5 +++--
>>  include/qemu/mmap-alloc.h |  2 ++
>>  backends/hostmem-file.c   |  2 +-
>>  exec.c                    | 18 +++++++++++-------
>>  softmmu/memory.c          |  7 +++++--
>>  util/mmap-alloc.c         | 10 ++++++----
>>  util/oslib-posix.c        |  2 +-
>>  8 files changed, 31 insertions(+), 17 deletions(-)
>>
>> diff --git a/include/exec/memory.h b/include/exec/memory.h
>> index 307e527835..1ae7b31e3a 100644
>> --- a/include/exec/memory.h
>> +++ b/include/exec/memory.h
>> @@ -884,6 +884,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
>>   *             - RAM_PMEM: the memory is persistent memory
>>   *             Other bits are ignored now.
>>   * @path: the path in which to allocate the RAM.
>> + * @readonly: true to open @path for reading, false for read/write.
>>   * @errp: pointer to Error*, to store an error if it happens.
>>   *
>>   * Note that this function does not do anything to cause the data in the
>> @@ -896,6 +897,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>>                                        uint64_t align,
>>                                        uint32_t ram_flags,
>>                                        const char *path,
>> +                                      bool readonly,
>>                                        Error **errp);
>>  
> [...]
>> diff --git a/softmmu/memory.c b/softmmu/memory.c
>> index af25987518..d228635bb3 100644
>> --- a/softmmu/memory.c
>> +++ b/softmmu/memory.c
>> @@ -1553,15 +1553,18 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>>                                        uint64_t align,
>>                                        uint32_t ram_flags,
>>                                        const char *path,
>> +                                      bool readonly,
>>                                        Error **errp)
>>  {
>>      Error *err = NULL;
>>      memory_region_init(mr, owner, name, size);
>>      mr->ram = true;
>> +    mr->readonly = readonly;
>>      mr->terminates = true;
>>      mr->destructor = memory_region_destructor_ram;
>>      mr->align = align;
>> -    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
>> +    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
>> +                                             readonly, &err);
>>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>>      if (err) {
>>          mr->size = int128_zero();
>> @@ -1585,7 +1588,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>>      mr->destructor = memory_region_destructor_ram;
>>      mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
>>                                             share ? RAM_SHARED : 0,
>> -                                           fd, &err);
>> +                                           fd, false, &err);
>>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>>      if (err) {
>>          mr->size = int128_zero();
>> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
>> index 27dcccd8ec..890fda6a35 100644
>> --- a/util/mmap-alloc.c
>> +++ b/util/mmap-alloc.c
>> @@ -85,9 +85,11 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
>>  void *qemu_ram_mmap(int fd,
>>                      size_t size,
>>                      size_t align,
>> +                    bool readonly,
>>                      bool shared,
>>                      bool is_pmem)
>>  {
>> +    int prot;
>>      int flags;
>>      int map_sync_flags = 0;
>>      int guardfd;
>> @@ -146,8 +148,9 @@ void *qemu_ram_mmap(int fd,
>>  
>>      offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
>>  
>> -    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
>> -               flags | map_sync_flags, fd, 0);
>> +    prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
>> +
>> +    ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
>>  
>>      if (ptr == MAP_FAILED && map_sync_flags) {
>>          if (errno == ENOTSUP) {
>> @@ -171,8 +174,7 @@ void *qemu_ram_mmap(int fd,
>>           * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
>>           * we will remove these flags to handle compatibility.
>>           */
>> -        ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
>> -                   flags, fd, 0);
>> +        ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
>>      }
>>  
>>      if (ptr == MAP_FAILED) {
> [...]
>
Stefan Hajnoczi Aug. 4, 2020, 1:47 p.m. UTC | #3
On Tue, Aug 04, 2020 at 02:26:22PM +0200, Philippe Mathieu-Daudé wrote:
> On 8/4/20 2:25 PM, Philippe Mathieu-Daudé wrote:
> > Hi Stefan,
> > 
> > On 8/4/20 12:12 PM, Stefan Hajnoczi wrote:
> >> There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
> >> creating a memory region from a file. This functionality is needed since
> >> the underlying host file may not allow writing.
> >>
> >> Add a bool readonly argument to memory_region_init_ram_from_file() and
> >> the APIs it calls.
> >>
> >> Extend memory_region_init_ram_from_file() rather than introducing a
> >> memory_region_init_rom_from_file() API so that callers can easily make a
> >> choice between read/write and read-only at runtime without calling
> >> different APIs.
> > 
> > What happens if we call:
> > 
> >  memory_region_init_ram_from_file(mr, ..., readonly=false, ...);
> >  memory_region_set_readonly(mr, false);
> 
> In case my error is not obvious, I meant:
> 
>    memory_region_init_ram_from_file(mr, ..., readonly=true, ...);
>    memory_region_set_readonly(mr, false);

Since the mmap was made using PROT_READ any store instructions to the
memory will fault.

Is there some scenario where memory_region_set_readonly() is called? I
can't find one.

Stefan
Philippe Mathieu-Daudé Aug. 4, 2020, 1:57 p.m. UTC | #4
On 8/4/20 3:47 PM, Stefan Hajnoczi wrote:
> On Tue, Aug 04, 2020 at 02:26:22PM +0200, Philippe Mathieu-Daudé wrote:
>> On 8/4/20 2:25 PM, Philippe Mathieu-Daudé wrote:
>>> Hi Stefan,
>>>
>>> On 8/4/20 12:12 PM, Stefan Hajnoczi wrote:
>>>> There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when
>>>> creating a memory region from a file. This functionality is needed since
>>>> the underlying host file may not allow writing.
>>>>
>>>> Add a bool readonly argument to memory_region_init_ram_from_file() and
>>>> the APIs it calls.
>>>>
>>>> Extend memory_region_init_ram_from_file() rather than introducing a
>>>> memory_region_init_rom_from_file() API so that callers can easily make a
>>>> choice between read/write and read-only at runtime without calling
>>>> different APIs.
>>>
>>> What happens if we call:
>>>
>>>  memory_region_init_ram_from_file(mr, ..., readonly=false, ...);
>>>  memory_region_set_readonly(mr, false);
>>
>> In case my error is not obvious, I meant:
>>
>>    memory_region_init_ram_from_file(mr, ..., readonly=true, ...);
>>    memory_region_set_readonly(mr, false);
> 
> Since the mmap was made using PROT_READ any store instructions to the
> memory will fault.
> 
> Is there some scenario where memory_region_set_readonly() is called? I
> can't find one.

Not in the current code base, but I was wondering about the API abuses.

I see in the next patch the property is protected:

    if (host_memory_backend_mr_inited(backend)) {
        error_setg(errp, "cannot change property 'readonly' of %s.",
                   object_get_typename(o));
        return;
    }

By using memory_region_set_readonly() you bypass this protection.

Maybe not something to worry.

Anyway for the patch:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> 
> Stefan
>
diff mbox series

Patch

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 307e527835..1ae7b31e3a 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -884,6 +884,7 @@  void memory_region_init_resizeable_ram(MemoryRegion *mr,
  *             - RAM_PMEM: the memory is persistent memory
  *             Other bits are ignored now.
  * @path: the path in which to allocate the RAM.
+ * @readonly: true to open @path for reading, false for read/write.
  * @errp: pointer to Error*, to store an error if it happens.
  *
  * Note that this function does not do anything to cause the data in the
@@ -896,6 +897,7 @@  void memory_region_init_ram_from_file(MemoryRegion *mr,
                                       uint64_t align,
                                       uint32_t ram_flags,
                                       const char *path,
+                                      bool readonly,
                                       Error **errp);
 
 /**
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 3ef729a23c..2a0360a0f2 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -110,6 +110,7 @@  long qemu_maxrampagesize(void);
  *              - RAM_PMEM: the backend @mem_path or @fd is persistent memory
  *              Other bits are ignored.
  *  @mem_path or @fd: specify the backing file or device
+ *  @readonly: true to open @path for reading, false for read/write.
  *  @errp: pointer to Error*, to store an error if it happens
  *
  * Return:
@@ -118,9 +119,9 @@  long qemu_maxrampagesize(void);
  */
 RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
                                    uint32_t ram_flags, const char *mem_path,
-                                   Error **errp);
+                                   bool readonly, Error **errp);
 RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
-                                 uint32_t ram_flags, int fd,
+                                 uint32_t ram_flags, int fd, bool readonly,
                                  Error **errp);
 
 RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index e786266b92..8b7a5c70f3 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -14,6 +14,7 @@  size_t qemu_mempath_getpagesize(const char *mem_path);
  *  @size: the number of bytes to be mmaped
  *  @align: if not zero, specify the alignment of the starting mapping address;
  *          otherwise, the alignment in use will be determined by QEMU.
+ *  @readonly: true for a read-only mapping, false for read/write.
  *  @shared: map has RAM_SHARED flag.
  *  @is_pmem: map has RAM_PMEM flag.
  *
@@ -24,6 +25,7 @@  size_t qemu_mempath_getpagesize(const char *mem_path);
 void *qemu_ram_mmap(int fd,
                     size_t size,
                     size_t align,
+                    bool readonly,
                     bool shared,
                     bool is_pmem);
 
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 5b819020b4..37c70acfe2 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -57,7 +57,7 @@  file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
                                      backend->size, fb->align,
                                      (backend->share ? RAM_SHARED : 0) |
                                      (fb->is_pmem ? RAM_PMEM : 0),
-                                     fb->mem_path, errp);
+                                     fb->mem_path, false, errp);
     g_free(name);
 #endif
 }
diff --git a/exec.c b/exec.c
index 6f381f98e2..5874e999ab 100644
--- a/exec.c
+++ b/exec.c
@@ -1769,6 +1769,7 @@  static int64_t get_file_align(int fd)
 
 static int file_ram_open(const char *path,
                          const char *region_name,
+                         bool readonly,
                          bool *created,
                          Error **errp)
 {
@@ -1779,7 +1780,7 @@  static int file_ram_open(const char *path,
 
     *created = false;
     for (;;) {
-        fd = open(path, O_RDWR);
+        fd = open(path, readonly ? O_RDONLY : O_RDWR);
         if (fd >= 0) {
             /* @path names an existing file, use it */
             break;
@@ -1831,6 +1832,7 @@  static int file_ram_open(const char *path,
 static void *file_ram_alloc(RAMBlock *block,
                             ram_addr_t memory,
                             int fd,
+                            bool readonly,
                             bool truncate,
                             Error **errp)
 {
@@ -1881,7 +1883,7 @@  static void *file_ram_alloc(RAMBlock *block,
         perror("ftruncate");
     }
 
-    area = qemu_ram_mmap(fd, memory, block->mr->align,
+    area = qemu_ram_mmap(fd, memory, block->mr->align, readonly,
                          block->flags & RAM_SHARED, block->flags & RAM_PMEM);
     if (area == MAP_FAILED) {
         error_setg_errno(errp, errno,
@@ -2313,7 +2315,7 @@  static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
 
 #ifdef CONFIG_POSIX
 RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
-                                 uint32_t ram_flags, int fd,
+                                 uint32_t ram_flags, int fd, bool readonly,
                                  Error **errp)
 {
     RAMBlock *new_block;
@@ -2367,7 +2369,8 @@  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
     new_block->used_length = size;
     new_block->max_length = size;
     new_block->flags = ram_flags;
-    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
+    new_block->host = file_ram_alloc(new_block, size, fd, readonly,
+                                     !file_size, errp);
     if (!new_block->host) {
         g_free(new_block);
         return NULL;
@@ -2386,18 +2389,19 @@  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
 
 RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
                                    uint32_t ram_flags, const char *mem_path,
-                                   Error **errp)
+                                   bool readonly, Error **errp)
 {
     int fd;
     bool created;
     RAMBlock *block;
 
-    fd = file_ram_open(mem_path, memory_region_name(mr), &created, errp);
+    fd = file_ram_open(mem_path, memory_region_name(mr), readonly, &created,
+                       errp);
     if (fd < 0) {
         return NULL;
     }
 
-    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
+    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, readonly, errp);
     if (!block) {
         if (created) {
             unlink(mem_path);
diff --git a/softmmu/memory.c b/softmmu/memory.c
index af25987518..d228635bb3 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1553,15 +1553,18 @@  void memory_region_init_ram_from_file(MemoryRegion *mr,
                                       uint64_t align,
                                       uint32_t ram_flags,
                                       const char *path,
+                                      bool readonly,
                                       Error **errp)
 {
     Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
+    mr->readonly = readonly;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
     mr->align = align;
-    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
+    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
+                                             readonly, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
     if (err) {
         mr->size = int128_zero();
@@ -1585,7 +1588,7 @@  void memory_region_init_ram_from_fd(MemoryRegion *mr,
     mr->destructor = memory_region_destructor_ram;
     mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
                                            share ? RAM_SHARED : 0,
-                                           fd, &err);
+                                           fd, false, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
     if (err) {
         mr->size = int128_zero();
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 27dcccd8ec..890fda6a35 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -85,9 +85,11 @@  size_t qemu_mempath_getpagesize(const char *mem_path)
 void *qemu_ram_mmap(int fd,
                     size_t size,
                     size_t align,
+                    bool readonly,
                     bool shared,
                     bool is_pmem)
 {
+    int prot;
     int flags;
     int map_sync_flags = 0;
     int guardfd;
@@ -146,8 +148,9 @@  void *qemu_ram_mmap(int fd,
 
     offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
 
-    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
-               flags | map_sync_flags, fd, 0);
+    prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
+
+    ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
 
     if (ptr == MAP_FAILED && map_sync_flags) {
         if (errno == ENOTSUP) {
@@ -171,8 +174,7 @@  void *qemu_ram_mmap(int fd,
          * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
          * we will remove these flags to handle compatibility.
          */
-        ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
-                   flags, fd, 0);
+        ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
     }
 
     if (ptr == MAP_FAILED) {
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index ad8001a4ad..236b3a88c1 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -227,7 +227,7 @@  void *qemu_memalign(size_t alignment, size_t size)
 void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
 {
     size_t align = QEMU_VMALLOC_ALIGN;
-    void *ptr = qemu_ram_mmap(-1, size, align, shared, false);
+    void *ptr = qemu_ram_mmap(-1, size, align, false, shared, false);
 
     if (ptr == MAP_FAILED) {
         return NULL;