[PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Marco Elver]

Setting up siginfo and using send_sig_info() and force_sig_info()
directly is discouraged. Instead, new code wanting to generate signals
should use the appropriate helper specific to the signal.

Eric mentioned that he'd like to make these static at some point, but
until that can happen, let's try to avoid introducing new users of them.

Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Marco Elver <elver@google.com>
---
Eric,

While siginfo doesn't need changing often, when it does, it's quite the
adventure. We now have the various static asserts. The other thing is
usage of {send,force}_sig_info.

I think the best option right now is to teach checkpatch.pl about it
until they become static.

Fyi, I noticed one such new user here:
https://lkml.kernel.org/r/20210421024826.13529-1-wangjunqiang@iscas.ac.cn

Thanks,
-- Marco
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ccb412a74725..3a86aafc3bcd 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7153,6 +7153,12 @@ sub process {
 			     "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
 		}
 
+# check for direct use of send_sig_info(), force_sig_info()
+		if ($line =~ /\b((force|send)_sig_info)\(/) {
+			WARN("USE_SIGINFO_HELPER",
+			     "Where possible, avoid using '$1' directly and use a signal-specific helper setting required siginfo fields (see include/linux/sched/signal.h).\n" . $herecurr);
+		}
+
 # check for deprecated apis
 		if ($line =~ /\b($deprecated_apis_search)\b\s*\(/) {
 			my $deprecated_api = $1;
-- 
2.31.1.607.g51e8a6a459-goog

Re: [PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Dwaipayan Ray]

On Thu, May 6, 2021 at 6:59 PM Marco Elver <elver@google.com> wrote:
>
> Setting up siginfo and using send_sig_info() and force_sig_info()
> directly is discouraged. Instead, new code wanting to generate signals
> should use the appropriate helper specific to the signal.
>
> Eric mentioned that he'd like to make these static at some point, but
> until that can happen, let's try to avoid introducing new users of them.
>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> Eric,
>
> While siginfo doesn't need changing often, when it does, it's quite the
> adventure. We now have the various static asserts. The other thing is
> usage of {send,force}_sig_info.
>
> I think the best option right now is to teach checkpatch.pl about it
> until they become static.
>
> Fyi, I noticed one such new user here:
> https://lkml.kernel.org/r/20210421024826.13529-1-wangjunqiang@iscas.ac.cn
>
> Thanks,
> -- Marco
> ---
>  scripts/checkpatch.pl | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index ccb412a74725..3a86aafc3bcd 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -7153,6 +7153,12 @@ sub process {
>                              "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
>                 }
>
> +# check for direct use of send_sig_info(), force_sig_info()
> +               if ($line =~ /\b((force|send)_sig_info)\(/) {

I think this might be a little better as:
if ($line =~ /\b((?:force|send)_sig_info)\(/) {

Otherwise it's good as it is.
Tested-by: Dwaipayan Ray <dwaipayanray1@gmail.com>

Thanks,
Dwaipayan.

> +                       WARN("USE_SIGINFO_HELPER",
> +                            "Where possible, avoid using '$1' directly and use a signal-specific helper setting required siginfo fields (see include/linux/sched/signal.h).\n" . $herecurr);
> +               }
> +
>  # check for deprecated apis
>                 if ($line =~ /\b($deprecated_apis_search)\b\s*\(/) {
>                         my $deprecated_api = $1;
> --
> 2.31.1.607.g51e8a6a459-goog
>

[PATCH v2] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Marco Elver]

Setting up siginfo and using send_sig_info() or force_sig_info()
directly is discouraged. Instead, new code wanting to generate signals
should use the appropriate helper specific to the signal.

Eric mentioned that he'd like to make these static at some point, but
until that can happen, let's try to avoid introducing new users of them.

Cc: Eric W. Biederman <ebiederm@xmission.com>
Tested-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
Signed-off-by: Marco Elver <elver@google.com>
---
v2:
* Use ?: because we don't need $2 (suggested by Dwaipayan Ray).

v1: https://lkml.kernel.org/r/20210506132827.3198497-1-elver@google.com
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ccb412a74725..59f6eb3a2026 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7153,6 +7153,12 @@ sub process {
 			     "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
 		}
 
+# check for direct use of send_sig_info(), force_sig_info()
+		if ($line =~ /\b((?:force|send)_sig_info)\(/) {
+			WARN("USE_SIGINFO_HELPER",
+			     "Where possible, avoid using '$1' directly and use a signal-specific helper setting required siginfo fields (see include/linux/sched/signal.h).\n" . $herecurr);
+		}
+
 # check for deprecated apis
 		if ($line =~ /\b($deprecated_apis_search)\b\s*\(/) {
 			my $deprecated_api = $1;
-- 
2.31.1.607.g51e8a6a459-goog

Re: [PATCH v2] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Joe Perches]

On Thu, 2021-05-06 at 17:22 +0200, Marco Elver wrote:
> Setting up siginfo and using send_sig_info() or force_sig_info()
> directly is discouraged. Instead, new code wanting to generate signals
> should use the appropriate helper specific to the signal.
> 
> Eric mentioned that he'd like to make these static at some point, but
> until that can happen, let's try to avoid introducing new users of them.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -7153,6 +7153,12 @@ sub process {
>  			     "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
>  		}
>  
> 
> +# check for direct use of send_sig_info(), force_sig_info()
> +		if ($line =~ /\b((?:force|send)_sig_info)\(/) {

You want to be able to find uses like 'force_sig_info (<foo>...'
so you should add a \s* after the capture group.
And it's probably simpler and more readable to use
		if ($sline =~ /\b(force_sig_info|send_sig_info)\s*\(/) {
instead of the more complex regex

(sline is stripped of comments, $line is not)

> +			WARN("USE_SIGINFO_HELPER",
> +			     "Where possible, avoid using '$1' directly and use a signal-specific helper setting required siginfo fields (see include/linux/sched/signal.h).\n" . $herecurr);

A rather long and complex sentence.
How about
	"Prefer signal-specific helpers over use of '$1' (see: include/linux/sched/signal.h)\n"

And in that signal.h file, there's no obvious reference to
these signal-specific helpers.  Is there a better reference
in the Documentation/ tree?

Re: [PATCH v2] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Marco Elver]

On Thu, 6 May 2021 at 23:41, Joe Perches <joe@perches.com> wrote:
> On Thu, 2021-05-06 at 17:22 +0200, Marco Elver wrote:
> > Setting up siginfo and using send_sig_info() or force_sig_info()
> > directly is discouraged. Instead, new code wanting to generate signals
> > should use the appropriate helper specific to the signal.
> >
> > Eric mentioned that he'd like to make these static at some point, but
> > until that can happen, let's try to avoid introducing new users of them.
> []
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
> > @@ -7153,6 +7153,12 @@ sub process {
> >                            "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
> >               }
> >
> >
> > +# check for direct use of send_sig_info(), force_sig_info()
> > +             if ($line =~ /\b((?:force|send)_sig_info)\(/) {
>
> You want to be able to find uses like 'force_sig_info (<foo>...'
> so you should add a \s* after the capture group.
> And it's probably simpler and more readable to use
>                 if ($sline =~ /\b(force_sig_info|send_sig_info)\s*\(/) {
> instead of the more complex regex
>
> (sline is stripped of comments, $line is not)

Done for v3.

> > +                     WARN("USE_SIGINFO_HELPER",
> > +                          "Where possible, avoid using '$1' directly and use a signal-specific helper setting required siginfo fields (see include/linux/sched/signal.h).\n" . $herecurr);
>
> A rather long and complex sentence.
> How about
>         "Prefer signal-specific helpers over use of '$1' (see: include/linux/sched/signal.h)\n"

Sounds good.

> And in that signal.h file, there's no obvious reference to
> these signal-specific helpers.  Is there a better reference
> in the Documentation/ tree?

Yeah, signal.h has their declarations, the definitions live in
kernel/signal.c. But otherwise, there's no better reference anywhere
AFAIK. The main thing here is to alert someone to double-check their
use of {send,force}_sig_info() -- when thinking what would have helped
me identify the problem earlier, I came to the conclusion that a
checkpatch.pl warning would have done exactly that. Like Eric said,
eventually these might become static, but it doesn't look trivial to
do this right now. When that happens, this check can then be removed
again. But since it might be a while, we can at least try to automate
this "trivial" review around siginfo.

I'll send v3 shortly.

Thanks,
-- Marco

Re: [PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Lukas Bulwahn]

On Thu, May 6, 2021 at 5:02 PM Dwaipayan Ray <dwaipayanray1@gmail.com> wrote:
>
> On Thu, May 6, 2021 at 6:59 PM Marco Elver <elver@google.com> wrote:
> >
> > Setting up siginfo and using send_sig_info() and force_sig_info()
> > directly is discouraged. Instead, new code wanting to generate signals
> > should use the appropriate helper specific to the signal.
> >
> > Eric mentioned that he'd like to make these static at some point, but
> > until that can happen, let's try to avoid introducing new users of them.
> >
> > Cc: Eric W. Biederman <ebiederm@xmission.com>
> > Signed-off-by: Marco Elver <elver@google.com>
> > ---
> > Eric,
> >
> > While siginfo doesn't need changing often, when it does, it's quite the
> > adventure. We now have the various static asserts. The other thing is
> > usage of {send,force}_sig_info.
> >
> > I think the best option right now is to teach checkpatch.pl about it
> > until they become static.
> >
> > Fyi, I noticed one such new user here:
> > https://lkml.kernel.org/r/20210421024826.13529-1-wangjunqiang@iscas.ac.cn
> >
> > Thanks,
> > -- Marco
> > ---
> >  scripts/checkpatch.pl | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > index ccb412a74725..3a86aafc3bcd 100755
> > --- a/scripts/checkpatch.pl
> > +++ b/scripts/checkpatch.pl
> > @@ -7153,6 +7153,12 @@ sub process {
> >                              "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
> >                 }
> >
> > +# check for direct use of send_sig_info(), force_sig_info()
> > +               if ($line =~ /\b((force|send)_sig_info)\(/) {
>
> I think this might be a little better as:
> if ($line =~ /\b((?:force|send)_sig_info)\(/) {
>
> Otherwise it's good as it is.
> Tested-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
>

Dwaipayan, do you want to also document this new rule on the
checkpatch documentation?
Marco, maybe you can assist us here with some pointer (lore.kernel.org
link) to the original discussion you had.

Lukas

Re: [PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Marco Elver]

On Thu, 6 May 2021 at 18:02, Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
> On Thu, May 6, 2021 at 5:02 PM Dwaipayan Ray <dwaipayanray1@gmail.com> wrote:
> > On Thu, May 6, 2021 at 6:59 PM Marco Elver <elver@google.com> wrote:
> > >
> > > Setting up siginfo and using send_sig_info() and force_sig_info()
> > > directly is discouraged. Instead, new code wanting to generate signals
> > > should use the appropriate helper specific to the signal.
> > >
> > > Eric mentioned that he'd like to make these static at some point, but
> > > until that can happen, let's try to avoid introducing new users of them.
> > >
> > > Cc: Eric W. Biederman <ebiederm@xmission.com>
> > > Signed-off-by: Marco Elver <elver@google.com>
> > > ---
> > > Eric,
> > >
> > > While siginfo doesn't need changing often, when it does, it's quite the
> > > adventure. We now have the various static asserts. The other thing is
> > > usage of {send,force}_sig_info.
> > >
> > > I think the best option right now is to teach checkpatch.pl about it
> > > until they become static.
> > >
> > > Fyi, I noticed one such new user here:
> > > https://lkml.kernel.org/r/20210421024826.13529-1-wangjunqiang@iscas.ac.cn
> > >
> > > Thanks,
> > > -- Marco
> > > ---
> > >  scripts/checkpatch.pl | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > > index ccb412a74725..3a86aafc3bcd 100755
> > > --- a/scripts/checkpatch.pl
> > > +++ b/scripts/checkpatch.pl
> > > @@ -7153,6 +7153,12 @@ sub process {
> > >                              "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
> > >                 }
> > >
> > > +# check for direct use of send_sig_info(), force_sig_info()
> > > +               if ($line =~ /\b((force|send)_sig_info)\(/) {
> >
> > I think this might be a little better as:
> > if ($line =~ /\b((?:force|send)_sig_info)\(/) {
> >
> > Otherwise it's good as it is.
> > Tested-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
> >
>
> Dwaipayan, do you want to also document this new rule on the
> checkpatch documentation?
> Marco, maybe you can assist us here with some pointer (lore.kernel.org
> link) to the original discussion you had.

It started somewhere here:
https://lkml.kernel.org/r/m17dkjttpj.fsf@fess.ebiederm.org

Eric has the full history here -- if I missed something, hopefully
he'll nack or ack.

Thanks,
-- Marco

Re: [PATCH] checkpatch: warn about direct use of send_sig_info and force_sig_info

[Eric W. Biederman]

Marco Elver <elver@google.com> writes:

> On Thu, 6 May 2021 at 18:02, Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
>> On Thu, May 6, 2021 at 5:02 PM Dwaipayan Ray <dwaipayanray1@gmail.com> wrote:
>> > On Thu, May 6, 2021 at 6:59 PM Marco Elver <elver@google.com> wrote:
>> > >
>> > > Setting up siginfo and using send_sig_info() and force_sig_info()
>> > > directly is discouraged. Instead, new code wanting to generate signals
>> > > should use the appropriate helper specific to the signal.
>> > >
>> > > Eric mentioned that he'd like to make these static at some point, but
>> > > until that can happen, let's try to avoid introducing new users of them.
>> > >
>> > > Cc: Eric W. Biederman <ebiederm@xmission.com>
>> > > Signed-off-by: Marco Elver <elver@google.com>
>> > > ---
>> > > Eric,
>> > >
>> > > While siginfo doesn't need changing often, when it does, it's quite the
>> > > adventure. We now have the various static asserts. The other thing is
>> > > usage of {send,force}_sig_info.
>> > >
>> > > I think the best option right now is to teach checkpatch.pl about it
>> > > until they become static.
>> > >
>> > > Fyi, I noticed one such new user here:
>> > > https://lkml.kernel.org/r/20210421024826.13529-1-wangjunqiang@iscas.ac.cn
>> > >
>> > > Thanks,
>> > > -- Marco
>> > > ---
>> > >  scripts/checkpatch.pl | 6 ++++++
>> > >  1 file changed, 6 insertions(+)
>> > >
>> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>> > > index ccb412a74725..3a86aafc3bcd 100755
>> > > --- a/scripts/checkpatch.pl
>> > > +++ b/scripts/checkpatch.pl
>> > > @@ -7153,6 +7153,12 @@ sub process {
>> > >                              "Where possible, use lockdep_assert_held instead of assertions based on spin_is_locked\n" . $herecurr);
>> > >                 }
>> > >
>> > > +# check for direct use of send_sig_info(), force_sig_info()
>> > > +               if ($line =~ /\b((force|send)_sig_info)\(/) {
>> >
>> > I think this might be a little better as:
>> > if ($line =~ /\b((?:force|send)_sig_info)\(/) {
>> >
>> > Otherwise it's good as it is.
>> > Tested-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
>> >
>>
>> Dwaipayan, do you want to also document this new rule on the
>> checkpatch documentation?
>> Marco, maybe you can assist us here with some pointer (lore.kernel.org
>> link) to the original discussion you had.
>
> It started somewhere here:
> https://lkml.kernel.org/r/m17dkjttpj.fsf@fess.ebiederm.org
>
> Eric has the full history here -- if I missed something, hopefully
> he'll nack or ack.

The practical problem is that siginfo_t is a complicated union.

Having fixed many many cases of this there is a very high probability in
making a mistake in filling siginfo_t.  Perhaps 1 in 10 times someone
fills out a siginfo_t manually.  So helpers that take just the
information that is intended to be in the structure as parameters and
fill in that information explicitly are a tremendous help, and let
developers when calling them focus on their actual development.

This all a very slow moving process and we don't have many call sites
for any kind of exception generating signals happen quickly.   Maybe one
or two a year.

I don't mind a checkpatch warning.  But making force_sig_info and
send_sig_info static is probably the better long term approach so people
simply don't have a problematic interface to call.

I will add that the ongoing addtion of SIGTRAP TRAP_PERF is currently
misusing si_errnno in Linus's tree.  We are reviewing and double
checking the fixes now.  Which is pretty much where this conversation
started this time around.

Eric