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Date:   Mon, 10 Oct 2022 09:38:11 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] sched: Introduce struct balance_callback to avoid CFI
 mismatches
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References: <20221008000758.2957718-1-keescook@chromium.org>
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On Fri, Oct 07, 2022 at 05:07:58PM -0700, Kees Cook wrote:
> Introduce distinct struct balance_callback instead of performing function
> pointer casting which will trip CFI. Avoids warnings as found by Clang's
> future -Wcast-function-type-strict option:
> 
> In file included from kernel/sched/core.c:84:
> kernel/sched/sched.h:1755:15: warning: cast from 'void (*)(struct rq *)' to 'void (*)(struct callback_head *)' converts to incompatible function type [-Wcast-function-type-strict]
>         head->func = (void (*)(struct callback_head *))func;
>                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> No binary differences result from this change.
> 
> This patch is a cleanup based on Brad Spengler/PaX Team's modifications
> to sched code in their last public patch of grsecurity/PaX based on my
> understanding of the code. Changes or omissions from the original code
> are mine and don't reflect the original grsecurity/PaX code.
> 
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1724
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  kernel/sched/core.c     | 24 ++++++++++++------------
>  kernel/sched/deadline.c |  4 ++--
>  kernel/sched/rt.c       |  4 ++--
>  kernel/sched/sched.h    | 14 ++++++++++----
>  4 files changed, 26 insertions(+), 20 deletions(-)

Thanks!