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

zhong jiang
2019-07-08T13:53:03Z

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