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Date: Tue, 19 Apr 2022 19:45:16 -0700 From: Kees Cook <keescook@...omium.org> To: joao@...rdrivepizza.com Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, peterz@...radead.org, jpoimboe@...hat.com, andrew.cooper3@...rix.com, samitolvanen@...gle.com, mark.rutland@....com, hjl.tools@...il.com, alyssa.milburn@...ux.intel.com, ndesaulniers@...gle.com, gabriel.gomes@...ux.intel.com, rick.p.edgecombe@...el.com Subject: Re: [RFC PATCH 10/11] linux/interrupt: Fix prototype matching property On Tue, Apr 19, 2022 at 05:42:40PM -0700, joao@...rdrivepizza.com wrote: > Unions will make function pointers with different prototypes be used through > the same call. This leads into the same call instruction being used for > calling functions with different prototypes, making them unsuitable for > prototype-based fine-grained CFI. Why? Shouldn't the callers be using different prototypes? > Fix this CFI policy violation by removing the function pointer union in > the tasklet struct. The good news is that tasklet is on the way out the door[1], so this may quickly become a non-issue, but also to that end, this fix is hardly a problem for a deprecated API... -Kees [1] https://lore.kernel.org/linux-hardening/20220419211658.11403-1-apais@linux.microsoft.com/ > > Signed-off-by: Joao Moreira <joao@...rdrivepizza.com> > --- > include/linux/interrupt.h | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h > index f40754caaefa..8d5504b0f20b 100644 > --- a/include/linux/interrupt.h > +++ b/include/linux/interrupt.h > @@ -650,10 +650,8 @@ struct tasklet_struct > unsigned long state; > atomic_t count; > bool use_callback; > - union { > - void (*func)(unsigned long data); > - void (*callback)(struct tasklet_struct *t); > - }; > + void (*func)(unsigned long data); > + void (*callback)(struct tasklet_struct *t); > unsigned long data; > }; > > -- > 2.35.1 > -- Kees Cook
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