linux-kernel - Re: [PATCH v4 25/29] um: Stop conflating task_struct::stack with thread

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Message-ID: <CALCETrUO7tj0hVNKeMC7zcgqqGxzmAv1QWL-oh-eMc0WjYxb+Q@mail.gmail.com>
Date:	Sun, 26 Jun 2016 16:49:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v4 25/29] um: Stop conflating task_struct::stack with thread_info

On Sun, Jun 26, 2016 at 4:40 PM, Brian Gerst <brgerst@...il.com> wrote:
> On Sun, Jun 26, 2016 at 5:55 PM, Andy Lutomirski <luto@...nel.org> wrote:
>> From: Linus Torvalds <torvalds@...ux-foundation.org>
>>
>> thread_info may move in the future, so use the accessors.
>>
>> [changelog written by Andy]
>> Message-Id: <CA+55aFxvZhBu9U1cqpVm4frv0p5mqu=0TxsSqE-=95ft8HvCVA@...l.gmail.com>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  arch/x86/um/ptrace_32.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
>> index ebd4dd6ef73b..14e8f6a628c2 100644
>> --- a/arch/x86/um/ptrace_32.c
>> +++ b/arch/x86/um/ptrace_32.c
>> @@ -191,7 +191,7 @@ int peek_user(struct task_struct *child, long addr, long data)
>>
>>  static int get_fpregs(struct user_i387_struct __user *buf, struct task_struct *child)
>>  {
>> -       int err, n, cpu = ((struct thread_info *) child->stack)->cpu;
>> +       int err, n, cpu = task_thread_info(child)->cpu;
>
> Shouldn't this use task_cpu() like in patch 23?
>

Indeed.  But blame Linus -- he wrote it :)

If I send a v5, I'll fix this in this patch.  Otherwise I'll send a
followup patch when this lands.  It doesn't matter immediately because
I'm not opting um into THREAD_INFO_IN_TASK.

--Andy