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 <l...@amacapital.net>
> AuthorDate: Wed, 17 Dec 2014 14:48:30 -0800
> Committer: Ingo Molnar <mi...@kernel.org>
> 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.
-hpa
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