Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210318171111.706303-1-samitolvanen@google.com> <20210318171111.706303-6-samitolvanen@google.com>
In-Reply-To: <20210318171111.706303-6-samitolvanen@google.com>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 18 Mar 2021 11:50:00 -0700
Message-ID: <CAKwvOd=fWs6g2Bf2a_bA58_-uoWtVmNQnvrPxNhio4R5qGjcMQ@mail.gmail.com>
Subject: Re: [PATCH v2 05/17] workqueue: use WARN_ON_FUNCTION_MISMATCH
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Will Deacon <will@kernel.org>, Jessica Yu <jeyu@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        bpf <bpf@vger.kernel.org>, linux-hardening@vger.kernel.org,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        PCI <linux-pci@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> With CONFIG_CFI_CLANG, a callback function passed to
> __queue_delayed_work from a module points to a jump table entry
> defined in the module instead of the one used in the core kernel,
> which breaks function address equality in this check:
>
>   WARN_ON_ONCE(timer->function != delayed_work_timer_fn);
>
> Use WARN_ON_FUNCTION_MISMATCH() instead to disable the warning
> when CFI and modules are both enabled.

Does __cficanonical help with such comparisons? Or would that be a
very invasive change, if the concern was to try to keep these checks
in place for CONFIG_CFI_CLANG?

>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  kernel/workqueue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 0d150da252e8..03fe07d2f39f 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1630,7 +1630,7 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
>         struct work_struct *work = &dwork->work;
>
>         WARN_ON_ONCE(!wq);
> -       WARN_ON_ONCE(timer->function != delayed_work_timer_fn);
> +       WARN_ON_FUNCTION_MISMATCH(timer->function, delayed_work_timer_fn);
>         WARN_ON_ONCE(timer_pending(timer));
>         WARN_ON_ONCE(!list_empty(&work->entry));
>
> --
> 2.31.0.291.g576ba9dcdaf-goog
>


--
Thanks,
~Nick Desaulniers