Re: [PATCH] sched: Introduce struct balance_callback to avoid CFI mismatches

[Peter Zijlstra]

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@xxxxxxxxxx>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1724
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Ben Segall <bsegall@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  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!