On Thu, Dec 18, 2014 at 8:59 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 12/18/2014 03:16 AM, tip-bot for Andy Lutomirski wrote:
>> Commit-ID: 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0
>> Gitweb: http://git.kernel.org/tip/3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0
>> Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> AuthorDate: Wed, 17 Dec 2014 14:48:30 -0800
>> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
>> CommitDate: Thu, 18 Dec 2014 12:12:26 +0100
>>
>> x86/tls: Don't validate lm in set_thread_area() after all
>>
>> It turns out that there's a lurking ABI issue. GCC, when
>> compiling this in a 32-bit program:
>>
>> struct user_desc desc = {
>> .entry_number = idx,
>> .base_addr = base,
>> .limit = 0xfffff,
>> .seg_32bit = 1,
>> .contents = 0, /* Data, grow-up */
>> .read_exec_only = 0,
>> .limit_in_pages = 1,
>> .seg_not_present = 0,
>> .useable = 0,
>> };
>>
>> will leave .lm uninitialized. This means that anything in the
>> kernel that reads user_desc.lm for 32-bit tasks is unreliable.
>>
>
> No, it won't. However, if you initialize this dynamically field by
> field rather than as an initializer, then you are correct.
>
I tried the code above in function scope.
--Andy
> -hpa
>
--
Andy Lutomirski
AMA Capital Management, LLC
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