Date: Sat, 4 Jul 2020 14:12:36 +0200 From: Oscar Carter <oscar.carter@....com> To: Helge Deller <deller@....de> Cc: Oscar Carter <oscar.carter@....com>, Kees Cook <keescook@...omium.org>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, "James E . J . Bottomley" <James.Bottomley@...senPartnership.com>, kernel-hardening@...ts.openwall.com, linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] parisc/kernel/ftrace: Remove function callback casts On Sat, Jun 27, 2020 at 10:09:40PM +0200, Helge Deller wrote: > On 27.06.20 15:43, Oscar Carter wrote: > > In an effort to enable -Wcast-function-type in the top-level Makefile to > > support Control Flow Integrity builds, remove all the function callback > > casts. > > > > To do this remove the cast to a function pointer type in the comparison > > statement and add to the right and left operand a cast to unsigned long > > type. This can be done since the comparison is against function address > > (these operands are not function calls). > > On some architectures (namely ia64, ppc64 and parisc64) function pointers > actually refer to function descriptors, which in turn point to the real > function address. The compiler usually takes care of such comparism. > That said, casting to "unsigned long" might break this... Ok, thanks for the clarification. Today I have learned about function descriptors. > > Signed-off-by: Oscar Carter <oscar.carter@....com> > > --- > > arch/parisc/kernel/ftrace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c > > index 1df0f67ed667..86b49a5fc049 100644 > > --- a/arch/parisc/kernel/ftrace.c > > +++ b/arch/parisc/kernel/ftrace.c > > @@ -64,7 +64,7 @@ void notrace __hot ftrace_function_trampoline(unsigned long parent, > > function_trace_op, regs); > > > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > > - if (ftrace_graph_return != (trace_func_graph_ret_t) ftrace_stub || > > + if ((unsigned long)ftrace_graph_return != (unsigned long)ftrace_stub || > > Untested, but maybe better use: > dereference_function_descriptor(ftrace_graph_return) != > dereference_function_descriptor(ftrace_stub) Thanks for point me to the right direction about this theme. I will do a new version and I will resend. > ? > Helge Regards, Oscar Carter
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