Re: [PATCH] mm: redefine the MAP_SHARED_VALIDATE to other value

[zhong jiang <zhongjiang@huawei.com>]

On 2019/7/8 17:20, Michal Hocko wrote:
> [Cc Dan]
>
> On Mon 08-07-19 16:05:41, zhong jiang wrote:
>> As the mman manual says, mmap should return fails when we assign
>> the flags to MAP_SHARED | MAP_PRIVATE.
>>
>> But In fact, We run the code successfully and unexpected.
> What is the code that you are running and what is the code version.
Just an following code, For example,
addr = mmap(ADDR, PAGE_SIZE, PROT_WRITE|PROT_EXEC, MAP_SHARED|MAP_PRIVATE, fildes, OFFSET);

We test it and works well in linux 4.19.   As the mmap manual says,  it should fails.
>> It is because MAP_SHARED_VALIDATE is introduced and equal to
>> MAP_SHARED | MAP_PRIVATE.
> This was a deliberate decision IIRC. Have a look at 1c9725974074 ("mm:
> introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap
> flags").
I  has seen the patch,  It introduce the issue.  but it only define the MAP_SHARED_VALIDATE incorrectly.
Maybe the author miss the condition that MAP_SHARED_VALIDATE is equal to MAP_PRIVATE | MAP_SHARE.


Thanks,
zhong jiang
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>> ---
>>  include/uapi/linux/mman.h                          | 2 +-
>>  tools/include/uapi/asm-generic/mman-common-tools.h | 2 +-
>>  tools/include/uapi/linux/mman.h                    | 2 +-
>>  3 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
>> index fc1a64c..1d3098e 100644
>> --- a/include/uapi/linux/mman.h
>> +++ b/include/uapi/linux/mman.h
>> @@ -14,7 +14,7 @@
>>  
>>  #define MAP_SHARED	0x01		/* Share changes */
>>  #define MAP_PRIVATE	0x02		/* Changes are private */
>> -#define MAP_SHARED_VALIDATE 0x03	/* share + validate extension flags */
>> +#define MAP_SHARED_VALIDATE 0x04	/* share + validate extension flags */
>>  
>>  /*
>>   * Huge page size encoding when MAP_HUGETLB is specified, and a huge page
>> diff --git a/tools/include/uapi/asm-generic/mman-common-tools.h b/tools/include/uapi/asm-generic/mman-common-tools.h
>> index af7d0d3..4fc44d2 100644
>> --- a/tools/include/uapi/asm-generic/mman-common-tools.h
>> +++ b/tools/include/uapi/asm-generic/mman-common-tools.h
>> @@ -18,6 +18,6 @@
>>  #ifndef MAP_SHARED
>>  #define MAP_SHARED	0x01		/* Share changes */
>>  #define MAP_PRIVATE	0x02		/* Changes are private */
>> -#define MAP_SHARED_VALIDATE 0x03	/* share + validate extension flags */
>> +#define MAP_SHARED_VALIDATE 0x04	/* share + validate extension flags */
>>  #endif
>>  #endif // __ASM_GENERIC_MMAN_COMMON_TOOLS_ONLY_H
>> diff --git a/tools/include/uapi/linux/mman.h b/tools/include/uapi/linux/mman.h
>> index fc1a64c..1d3098e 100644
>> --- a/tools/include/uapi/linux/mman.h
>> +++ b/tools/include/uapi/linux/mman.h
>> @@ -14,7 +14,7 @@
>>  
>>  #define MAP_SHARED	0x01		/* Share changes */
>>  #define MAP_PRIVATE	0x02		/* Changes are private */
>> -#define MAP_SHARED_VALIDATE 0x03	/* share + validate extension flags */
>> +#define MAP_SHARED_VALIDATE 0x04	/* share + validate extension flags */
>>  
>>  /*
>>   * Huge page size encoding when MAP_HUGETLB is specified, and a huge page
>> -- 
>> 1.7.12.4