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

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

[Marco Elver]

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@intel.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@google.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@intel.com>
Signed-off-by: Marco Elver <elver@google.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);
 }
 
-- 
2.31.1.295.g9ea45b61b8-goog

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

[Peter Zijlstra]

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@intel.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@google.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@intel.com>
> Signed-off-by: Marco Elver <elver@google.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);
 	}

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

[Marco Elver]

On Thu, Apr 15, 2021 at 10:48AM +0200, Peter Zijlstra wrote:
> 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@intel.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
> > 
[...]
> 
> 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?

Thanks, that works for me. Do note that I explicitly chose u64 for
sig_addr/pending_addr because data->addr is u64. There might be a new
warning about the u64 to unsigned long assignment on 32 bit arches.

Perhaps it needs something ugly like this:

	info.si_addr = (void __user *)(unsigned long)event->pending_addr;

if pending_addr wants to be u64. Or just

	event->pending_addr = (unsigned long)data->addr;

if data->addr being u64 on 32 bit arches is simply overkill.

Thanks,
-- Marco

> ---
> 
> --- 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);
>  	}

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

[Peter Zijlstra]

On Thu, Apr 15, 2021 at 11:03:09AM +0200, Marco Elver wrote:
> On Thu, Apr 15, 2021 at 10:48AM +0200, Peter Zijlstra wrote:

> > I've ended up with the below delta, does that work for you?
> 
> Thanks, that works for me. Do note that I explicitly chose u64 for
> sig_addr/pending_addr because data->addr is u64. There might be a new
> warning about the u64 to unsigned long assignment on 32 bit arches.

My local i386-defconfig build seemed happy now. Mostly I think you're
allowed to silently truncate between base integer types. We'll see..
maybe some other compiler.

> Perhaps it needs something ugly like this:
> 
> 	info.si_addr = (void __user *)(unsigned long)event->pending_addr;
> 
> if pending_addr wants to be u64. Or just
> 
> 	event->pending_addr = (unsigned long)data->addr;
> 
> if data->addr being u64 on 32 bit arches is simply overkill.

Yeah it is. It's u64 for data layout purposes, the perf buffer works in
u64 chunks.