linux-kernel - Re: [peterz-queue:perf/core 18/22] kernel/events/core.c:6418:22: sparse: sparse: incorrect type in assignment (different address spaces)

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Date:   Thu, 15 Apr 2021 10:48:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     kbuild-all@...ts.01.org, kernel test robot <lkp@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [peterz-queue:perf/core 18/22] kernel/events/core.c:6418:22:
 sparse: sparse: incorrect type in assignment (different address spaces)

On Wed, Apr 14, 2021 at 04:33:22PM +0200, Marco Elver wrote:
> On Wed, Apr 14, 2021 at 10:10PM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/core
> > head:   0da503cd07380952599b67ded6efe030d78ea42d
> > commit: c7d4112e9f0e69edd649665836ce72008b95ab9f [18/22] perf: Add support for SIGTRAP on perf events
> [...]
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@...el.com>
> [...]
> >   6416		info.si_errno = event->attr.type;
> >   6417		info.si_perf = event->attr.sig_data;
> > > 6418		info.si_addr = (void *)event->sig_addr;
> >   6419		force_sig_info(&info);
> 
> I think it wants the below (feel free to squash into "perf: Add support
> for SIGTRAP on perf events").
> 
> Thanks,
> -- Marco
> 
> ------ >8 ------
> 
> From: Marco Elver <elver@...gle.com>
> Date: Wed, 14 Apr 2021 16:26:26 +0200
> Subject: [PATCH] perf: Fix cast to void __user pointer
> 
> sparse let us know that si_addr is 'void __user *', therefore add the
> missing __user attribute to the cast.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 1d2077389c0c..2677438ed668 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6414,7 +6414,7 @@ static void perf_sigtrap(struct perf_event *event)
>  	info.si_code = TRAP_PERF;
>  	info.si_errno = event->attr.type;
>  	info.si_perf = event->attr.sig_data;
> -	info.si_addr = (void *)event->sig_addr;
> +	info.si_addr = (void __user *)event->sig_addr;
>  	force_sig_info(&info);
>  }

Now the silly robot complains about:

CC      kernel/events/core.o
../kernel/events/core.c: In function ‘perf_sigtrap’:
../kernel/events/core.c:6418:17: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
6418 |  info.si_addr = (void __user *)event->sig_addr;

for all 32bit builds (because sig_addr is u64 and the pointer cast
truncates bits).

This had me look a little harder at sig_addr and I figured it should be
next to the pending fields for cache locality.

I've ended up with the below delta, does that work for you?

---

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -735,6 +735,7 @@ struct perf_event {
 	int				pending_wakeup;
 	int				pending_kill;
 	int				pending_disable;
+	unsigned long			pending_addr;	/* SIGTRAP */
 	struct irq_work			pending;
 
 	atomic_t			event_limit;
@@ -778,9 +779,6 @@ struct perf_event {
 	void *security;
 #endif
 	struct list_head		sb_list;
-
-	/* Address associated with event, which can be passed to siginfo_t. */
-	u64				sig_addr;
 #endif /* CONFIG_PERF_EVENTS */
 };
 
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6415,7 +6415,7 @@ static void perf_sigtrap(struct perf_eve
 	info.si_code = TRAP_PERF;
 	info.si_errno = event->attr.type;
 	info.si_perf = event->attr.sig_data;
-	info.si_addr = (void __user *)event->sig_addr;
+	info.si_addr = (void __user *)event->pending_addr;
 	force_sig_info(&info);
 }
 
@@ -9137,7 +9137,7 @@ static int __perf_event_overflow(struct
 	if (events && atomic_dec_and_test(&event->event_limit)) {
 		ret = 1;
 		event->pending_kill = POLL_HUP;
-		event->sig_addr = data->addr;
+		event->pending_addr = data->addr;
 
 		perf_event_disable_inatomic(event);
 	}