This can avoid the NULL-deref if the rm doesn't has a
read/write nor write/read_with_attrs callback.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
---
 memory.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/memory.c b/memory.c
index d14c6dec1d..3baf5857b9 100644
--- a/memory.c
+++ b/memory.c
@@ -1377,13 +1377,15 @@ static MemTxResult memory_region_dispatch_read1(MemoryRegion *mr,
                                          mr->ops->impl.max_access_size,
                                          memory_region_read_accessor,
                                          mr, attrs);
-    } else {
+    } else if (mr->ops->read_with_attrs) {
         return access_with_adjusted_size(addr, pval, size,
                                          mr->ops->impl.min_access_size,
                                          mr->ops->impl.max_access_size,
                                          memory_region_read_with_attrs_accessor,
                                          mr, attrs);
     }
+
+    return MEMTX_DECODE_ERROR;
 }
 
 MemTxResult memory_region_dispatch_read(MemoryRegion *mr,
@@ -1454,7 +1456,7 @@ MemTxResult memory_region_dispatch_write(MemoryRegion *mr,
                                          mr->ops->impl.max_access_size,
                                          memory_region_write_accessor, mr,
                                          attrs);
-    } else {
+    } else if (mr->ops->write_with_attrs) {
         return
             access_with_adjusted_size(addr, &data, size,
                                       mr->ops->impl.min_access_size,
@@ -1462,6 +1464,8 @@ MemTxResult memory_region_dispatch_write(MemoryRegion *mr,
                                       memory_region_write_with_attrs_accessor,
                                       mr, attrs);
     }
+
+    return MEMTX_DECODE_ERROR;
 }
 
 void memory_region_init_io(MemoryRegion *mr,
-- 
2.11.0

On 13 November 2018 at 01:42, Li Qiang <liq3ea@gmail.com> wrote:
> This can avoid the NULL-deref if the rm doesn't has a
> read/write nor write/read_with_attrs callback.
>
> Signed-off-by: Li Qiang <liq3ea@gmail.com>
> ---
>  memory.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

Alternative approach -- assert that every MemoryRegionOps has
pointers to callbacks in it, when it is registered in memory_region_init_io()
and memory_region_init_rom_device_nomigrate().

I don't have a strong opinion on which is better, but I guess
I slightly favour requiring devices to be specific about what
their read/write behaviour is.

Do we have many devices that legitimately only want to implement
one of read and write, not both ?

thanks
-- PMM

Peter Maydell <peter.maydell@linaro.org> 于2018年11月13日周二 下午5:49写道：

> On 13 November 2018 at 01:42, Li Qiang <liq3ea@gmail.com> wrote:
> > This can avoid the NULL-deref if the rm doesn't has a
> > read/write nor write/read_with_attrs callback.
> >
> > Signed-off-by: Li Qiang <liq3ea@gmail.com>
> > ---
> >  memory.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
>
> Alternative approach -- assert that every MemoryRegionOps has
> pointers to callbacks in it, when it is registered in
> memory_region_init_io()
>

Actually I have considered this approach, but I rember Paolo remind me that
some
of this MR without read callback's is valid because the read can never be
called, such as
'notdirty_mem_ops'. So I choose add a check here.



> and memory_region_init_rom_device_nomigrate().
>
> I don't have a strong opinion on which is better, but I guess
> I slightly favour requiring devices to be specific about what
> their read/write behaviour is.
>
> Do we have many devices that legitimately only want to implement
> one of read and write, not both ?


AFAICS, the device has just one read or write is not uncommon.
But nearly all of them implement a nop function does nothing.
So there just very little lack of the read or write function.

Thanks,
Li Qiang


>
> thanks
> -- PMM
>

Ping...

It makes sense as when we use 'memory_region_read_accessor' we check
mr->ops->read.
but when we use 'memory_region_read_with_attrs_accessor', we doesn't check
this.

Thanks,
Li Qiang

Li Qiang <liq3ea@gmail.com> 于2018年11月13日周二 上午9:42写道：

> This can avoid the NULL-deref if the rm doesn't has a
> read/write nor write/read_with_attrs callback.
>
> Signed-off-by: Li Qiang <liq3ea@gmail.com>
> ---
>  memory.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index d14c6dec1d..3baf5857b9 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1377,13 +1377,15 @@ static MemTxResult
> memory_region_dispatch_read1(MemoryRegion *mr,
>                                           mr->ops->impl.max_access_size,
>                                           memory_region_read_accessor,
>                                           mr, attrs);
> -    } else {
> +    } else if (mr->ops->read_with_attrs) {
>          return access_with_adjusted_size(addr, pval, size,
>                                           mr->ops->impl.min_access_size,
>                                           mr->ops->impl.max_access_size,
>
> memory_region_read_with_attrs_accessor,
>                                           mr, attrs);
>      }
> +
> +    return MEMTX_DECODE_ERROR;
>  }
>
>  MemTxResult memory_region_dispatch_read(MemoryRegion *mr,
> @@ -1454,7 +1456,7 @@ MemTxResult
> memory_region_dispatch_write(MemoryRegion *mr,
>                                           mr->ops->impl.max_access_size,
>                                           memory_region_write_accessor, mr,
>                                           attrs);
> -    } else {
> +    } else if (mr->ops->write_with_attrs) {
>          return
>              access_with_adjusted_size(addr, &data, size,
>                                        mr->ops->impl.min_access_size,
> @@ -1462,6 +1464,8 @@ MemTxResult
> memory_region_dispatch_write(MemoryRegion *mr,
>
>  memory_region_write_with_attrs_accessor,
>                                        mr, attrs);
>      }
> +
> +    return MEMTX_DECODE_ERROR;
>  }
>
>  void memory_region_init_io(MemoryRegion *mr,
> --
> 2.11.0
>
>