Hi, Kees,
Thanks a lot for your testing and the small testing case.
I just studied the root cause of this bug, and found that it’s because the call
to “__builtin_clear_padding()” should NOT be inserted BEFORE
the variable initialization. It should be inserted AFTER the variable
initialization.
Currently since the call to “__builtin_clear_padding()” is inserted Before the
variable initialization like the following:
__builtin_clear_padding (&obj, 0B, 1);
obj = {};
obj.val = val;
Then as a result, the reference to “obj” in the call to
“__builtin_clear_padding” is considered as an uninitialized usage.
I will move the call to __builtin_clear_padding after the variable
initialization.
Thanks.
Qing
> On Jul 28, 2021, at 3:21 PM, Kees Cook <[email protected]> wrote:
>
> On Tue, Jul 27, 2021 at 03:26:00AM +0000, Qing Zhao wrote:
>> This is the 6th version of the patch for the new security feature for GCC.
>>
>> I have tested it with bootstrap on both x86 and aarch64, regression testing
>> on both x86 and aarch64.
>> Also compile CPU2017 (running is ongoing), without any issue. (With the fix
>> to bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101586).
>>
>> Please take a look and let me know any issue.
>
> Good news, this passes all my initialization tests in the kernel. Yay! :)
>
> However, I see an unexpected side-effect from some static initializations:
>
> net/core/sock.c: In function 'sock_no_sendpage':
> net/core/sock.c:2849:23: warning: 'msg' is used uninitialized
> [-Wuninitialized]
> 2849 | struct msghdr msg = {.msg_flags = flags};
> | ^~~
>
> It seems like -Wuninitialized has suddenly stopped noticing explicit
> static initializers when there are bit fields in the struct. Here's a
> minimized case:
>
> $ cat init.c
> struct weird {
> int bit : 1;
> int val;
> };
>
> int func(int val)
> {
> struct weird obj = { .val = val };
> return obj.val;
> }
>
> $ gcc -c -o init.o -Wall -O2 -ftrivial-auto-var-init=zero init.c
> init.c: In function ‘func’:
> init.c:8:22: warning: ‘obj’ is used uninitialized [-Wuninitialized]
> 8 | struct weird obj = { .val = val };
> | ^~~
> init.c:8:22: note: ‘obj’ declared here
> 8 | struct weird obj = { .val = val };
> | ^~~
>
>
>
> --
> Kees Cook
