linux-kernel - Re: [PATCH v4 2/2] cpufreq: make interface functions and lock holding state clear

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 12 May 2022 18:23:52 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] cpufreq: make interface functions and lock holding
 state clear

On Thu, May 12, 2022 at 6:01 PM Schspa Shi <schspa@...il.com> wrote:
>
> "Rafael J. Wysocki" <rafael@...nel.org> writes:
>
> > On Thu, May 12, 2022 at 3:52 PM Schspa Shi <schspa@...il.com> wrote:
> >>
> >> cpufreq_offline() calls offline() and exit() under the policy rwsem
> >> But they are called outside the rwsem in cpufreq_online().
> >>
> >> This patch move the offline(), exit(), online(), init() to be inside
> >> of policy rwsem to achieve a clear lock relationship.
> >>
> >> All the init() online() implement only initialize policy object without
> >> holding this lock and won't call cpufreq APIs need to hold this lock.
> >>
> >> Signed-off-by: Schspa Shi <schspa@...il.com>
> >
> > IMV this still addresses 2 different issues and so it should be split
> > into 2 different patches.
> >
> >> ---
> >>  drivers/cpufreq/cpufreq.c | 5 ++---
> >>  1 file changed, 2 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> >> index 35dffd738580..f242d5488364 100644
> >> --- a/drivers/cpufreq/cpufreq.c
> >> +++ b/drivers/cpufreq/cpufreq.c
> >
> > Patch 1:
> >
> >> @@ -1343,12 +1343,12 @@ static int cpufreq_online(unsigned int cpu)
> >>                 down_write(&policy->rwsem);
> >>                 policy->cpu = cpu;
> >>                 policy->governor = NULL;
> >> -               up_write(&policy->rwsem);
> >>         } else {
> >>                 new_policy = true;
> >>                 policy = cpufreq_policy_alloc(cpu);
> >>                 if (!policy)
> >>                         return -ENOMEM;
> >> +               down_write(&policy->rwsem);
> >>         }
> >>
> >>         if (!new_policy && cpufreq_driver->online) {
> >> @@ -1388,7 +1388,6 @@ static int cpufreq_online(unsigned int cpu)
> >>                 cpumask_copy(policy->related_cpus, policy->cpus);
> >>         }
> >>
> >> -       down_write(&policy->rwsem);
> >>         /*
> >>          * affected cpus must always be the one, which are online. We aren't
> >>          * managing offline cpus here.
> >
> > which addresses the problem that cpufreq_online() updates the
> > policy->cpus and related_cpus masks without holding the policy rwsem
> > (since the policy kobject has been registered already at this point,
> > this is generally unsafe).
> >
> > A side-effect of it is that ->online() and ->init() will be called
> > under the policy rwsem now, but that should be fine and is more
> > consistent than the current code too.
> >
> > Patch 2:
> >
> >> @@ -1540,7 +1539,6 @@ static int cpufreq_online(unsigned int cpu)
> >>                 remove_cpu_dev_symlink(policy, get_cpu_device(j));
> >>
> >>         cpumask_clear(policy->cpus);
> >> -       up_write(&policy->rwsem);
> >>
> >>  out_offline_policy:
> >>         if (cpufreq_driver->offline)
> >> @@ -1549,6 +1547,7 @@ static int cpufreq_online(unsigned int cpu)
> >>  out_exit_policy:
> >>         if (cpufreq_driver->exit)
> >>                 cpufreq_driver->exit(policy);
> >> +       up_write(&policy->rwsem);
> >>
> >>  out_free_policy:
> >>         cpufreq_policy_free(policy);
> >> --
> >
> > which addressed the issue of calling ->offline() and ->exit() without
> > holding the policy rwsem that is at best inconsistent with
> > cpufreq_offline().
>
> No, we can't split this into two different patches. which will cause a
> uninitialized unlock for policy rwsem.
> This will make the git bitsec unusable.
>
> Which Dan Carpenter reported, and cause the patch of the v1 version to
> be reverted.
>
> Link: https://lore.kernel.org/all/YnKZCGaig+EXSowf@kili/

Ah, OK.  Never mind.