linux-kernel - Re: [PATCH v2] KEYS: trusted: Remove redundant static calls usage

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Message-ID: <CAFA6WYNamspdK=RakirdS3fiHrmmaPXcgEcZeNn5z2DRNdE3Rw@mail.gmail.com>
Date:   Tue, 10 Oct 2023 18:44:47 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     torvalds@...ux-foundation.org, peterz@...radead.org,
        zohar@...ux.ibm.com, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org, jejb@...ux.ibm.com,
        David.Kaplan@....com, bp@...en8.de, mingo@...nel.org,
        x86@...nel.org, regressions@...mhuis.info,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [PATCH v2] KEYS: trusted: Remove redundant static calls usage

On Tue, 10 Oct 2023 at 18:03, Jarkko Sakkinen <jarkko@...nel.org> wrote:
>
> On Fri, 2023-10-06 at 10:48 +0530, Sumit Garg wrote:
> > Static calls invocations aren't well supported from module __init and
> > __exit functions. Especially the static call from cleanup_trusted() led
> > to a crash on x86 kernel with CONFIG_DEBUG_VIRTUAL=y.
> >
> > However, the usage of static call invocations for trusted_key_init()
> > and trusted_key_exit() don't add any value from either a performance or
> > security perspective. Hence switch to use indirect function calls instead.
> >
> > Note here that although it will fix the current crash report, ultimately
> > the static call infrastructure should be fixed to either support its
> > future usage from module __init and __exit functions or not.
> >
> > Reported-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> > Link: https://lore.kernel.org/lkml/ZRhKq6e5nF%2F4ZIV1@fedora/#t
> > Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> > Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> > ---
> >
> > Changes in v2:
> > - Polish commit message as per comments from Mimi
> >
> >  security/keys/trusted-keys/trusted_core.c | 13 +++++--------
> >  1 file changed, 5 insertions(+), 8 deletions(-)
> >
> > diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
> > index c6fc50d67214..85fb5c22529a 100644
> > --- a/security/keys/trusted-keys/trusted_core.c
> > +++ b/security/keys/trusted-keys/trusted_core.c
> > @@ -44,13 +44,12 @@ static const struct trusted_key_source trusted_key_sources[] = {
> >  #endif
> >  };
> >
> > -DEFINE_STATIC_CALL_NULL(trusted_key_init, *trusted_key_sources[0].ops->init);
> >  DEFINE_STATIC_CALL_NULL(trusted_key_seal, *trusted_key_sources[0].ops->seal);
> >  DEFINE_STATIC_CALL_NULL(trusted_key_unseal,
> >                         *trusted_key_sources[0].ops->unseal);
> >  DEFINE_STATIC_CALL_NULL(trusted_key_get_random,
> >                         *trusted_key_sources[0].ops->get_random);
> > -DEFINE_STATIC_CALL_NULL(trusted_key_exit, *trusted_key_sources[0].ops->exit);
> > +static void (*trusted_key_exit)(void);
> >  static unsigned char migratable;
> >
> >  enum {
> > @@ -359,19 +358,16 @@ static int __init init_trusted(void)
> >                 if (!get_random)
> >                         get_random = kernel_get_random;
> >
> > -               static_call_update(trusted_key_init,
> > -                                  trusted_key_sources[i].ops->init);
> >                 static_call_update(trusted_key_seal,
> >                                    trusted_key_sources[i].ops->seal);
> >                 static_call_update(trusted_key_unseal,
> >                                    trusted_key_sources[i].ops->unseal);
> >                 static_call_update(trusted_key_get_random,
> >                                    get_random);
> > -               static_call_update(trusted_key_exit,
> > -                                  trusted_key_sources[i].ops->exit);
> > +               trusted_key_exit = trusted_key_sources[i].ops->exit;
> >                 migratable = trusted_key_sources[i].ops->migratable;
> >
> > -               ret = static_call(trusted_key_init)();
> > +               ret = trusted_key_sources[i].ops->init();
> >                 if (!ret)
> >                         break;
> >         }
> > @@ -388,7 +384,8 @@ static int __init init_trusted(void)
> >
> >  static void __exit cleanup_trusted(void)
> >  {
> > -       static_call_cond(trusted_key_exit)();
> > +       if (trusted_key_exit)
> > +               (*trusted_key_exit)();
> >  }
> >
> >  late_initcall(init_trusted);
>
> Would it be less confusing to require trusted_key_exit from each?
>

It is already required for each trust source to provide exit callback
but this NULL check was added via this fix [1] in case there isn't any
trust source present.

[1] https://lkml.kernel.org/stable/20220126184155.220814-1-dave.kleikamp@oracle.com/

-Sumit

> BR, Jarkko
>