Re: [PATCH v2] arm64: add ptrace regsets for ptrauth key management

From: Dave Martin <Dave.Martin@arm.com>
To: Kristina Martsenko <kristina.martsenko@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Amit Kachhap <amit.kachhap@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64: add ptrace regsets for ptrauth key management
Date: Wed, 23 Jan 2019 11:23:34 +0000	[thread overview]
Message-ID: <20190123112332.GL3578@e103592.cambridge.arm.com> (raw)
In-Reply-To: <b8afbda4-c782-ceee-8294-a96a1fec02df@arm.com>

On Tue, Jan 22, 2019 at 07:08:25PM +0000, Kristina Martsenko wrote:
> On 16/01/2019 15:13, Dave Martin wrote:
> > On Tue, Jan 15, 2019 at 07:32:30PM +0000, Kristina Martsenko wrote:
> >> On 11/01/2019 13:58, Dave Martin wrote:
> >>> On Thu, Jan 10, 2019 at 07:41:15PM +0000, Kristina Martsenko wrote:
> >>>> On 10/01/2019 19:35, Kristina Martsenko wrote:
> >>>> @@ -80,12 +65,12 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
> >>>>  #define ptrauth_thread_init_user(tsk)					\
> >>>>  do {									\
> >>>>  	struct task_struct *__ptiu_tsk = (tsk);				\
> >>>
> >>> Not added by this patch, but __ptiu_tsk doesn't seem to do anything
> >>> except make the subsquent lines more verbose than otherwise (and pollute
> >>> the identifier namespace -- though unlikely to be a problem).
> >>>
> >>> It may not be worth dropping it now that it's there though.
> >>
> >> Using __ptiu_tsk prevents the argument (tsk) from being evaluated twice,
> >> which could have side effects.
> > 
> > Ah, right.
> > 
> > Actually, could this be a function instead?  That would avoid multiple-
> > evaulation a clean way.
> 
> If it were a function, then this file (pointer_auth.h) would need to
> #include <linux/sched.h> (for the struct task_struct definition), which
> would create a circular header dependency, since sched.h #includes
> asm/processor.h, which #includes pointer_auth.h. Alternatively the
> function could be moved to pointer_auth.c, but that would prevent it
> from being inlined, so I'd prefer to keep it as a macro for now.

Ah, right -- I hit that before in a couple of places.

So long as there's a reason for these things being macros, I see
no problem.

> 
> >>>> -	ptrauth_keys_init(&__ptiu_tsk->thread.keys_user);		\
> >>>> -	ptrauth_keys_switch(&__ptiu_tsk->thread.keys_user);		\
> >>>> +	ptrauth_keys_init(&__ptiu_tsk->thread.uw.keys_user);		\
> >>>> +	ptrauth_keys_switch(&__ptiu_tsk->thread.uw.keys_user);		\
> >>>>  } while (0)
> >>>>  
> >>>>  #define ptrauth_thread_switch(tsk)	\
> >>>> -	ptrauth_keys_switch(&(tsk)->thread.keys_user)
> >>>> +	ptrauth_keys_switch(&(tsk)->thread.uw.keys_user)
> > 
> > Similarly, can this be a function?
> 
> Same reasons as above.
> 
> > (Technically tsk may be evaulated twice in this macro.  Given the way
> > these macros are used, I'm not sure that matters though.)
> 
> tsk is only used once here, so I think it's only evaluated once.

You're right ... I misread the changed line in the diff for two added
lines (doh).

Cheers
---Dave

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