All of
 help / color / mirror / Atom feed
From: Steven Rostedt <>
To: Jann Horn <>
Cc: LKML <>,
	Ingo Molnar <>, Kees Cook <>,
	Kernel Hardening <>,
	Oscar Carter <>,
	Andrew Morton <>
Subject: Re: [PATCH] tracing: Use linker magic instead of recasting ftrace_ops_list_func()
Date: Wed, 17 Jun 2020 18:36:28 -0400	[thread overview]
Message-ID: <20200617183628.3594271d@oasis.local.home> (raw)
In-Reply-To: <>

On Wed, 17 Jun 2020 23:30:07 +0200
Jann Horn <> wrote:
> [...]
> > +/* Defined by see the commment above arch_ftrace_ops_list_func for details */
> > +void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
> > +                         struct ftrace_ops *op, struct pt_regs *regs);  
> [...]
> > +void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
> >  {  
> Well, it's not like the function cast itself is the part that's
> problematic for CFI; the problematic part is when you actually make a
> C function call (in particular an indirect one) where the destination
> is compiled with a prototype that is different from the prototype used
> at the call site. Doing this linker hackery isn't really any better
> than shutting up the compiler warning by piling on enough casts or
> whatever. (There should be some combination of casts that'll shut up
> this warning, right?)

It's not called by C, it's called by assembly.

> IIUC the real issue here is that ftrace_func_t is defined as a fixed
> type, but actually has different types depending on the architecture?
> If so, it might be cleaner to define ftrace_func_t differently
> depending on architecture, or something like that?

There's functions that use this type.

When you register a function to be used by the function tracer (that
will have 4 parameters). If the arch supports it, it will call it
directly from the trampoline in assembly, but if it does not, then the
C code will only let assembly call the two parameter version, that will
call the 4 parameter function (adding NULLs to the extra two arguments). 

> And if that's not feasible, I think it would be better to at least
> replace this linker trickery with straightforward
> shut-up-the-compiler-casts - it'd be much easier to understand what's
> actually going on that way.

OK, what's the way to shut up the compiler for it, and we can have that

-- Steve

  reply	other threads:[~2020-06-17 22:36 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-17 20:56 [PATCH] tracing: Use linker magic instead of recasting ftrace_ops_list_func() Steven Rostedt
2020-06-17 21:30 ` Jann Horn
2020-06-17 21:30   ` Jann Horn
2020-06-17 22:36   ` Steven Rostedt [this message]
2020-06-17 23:12     ` Jann Horn
2020-06-17 23:12       ` Jann Horn
2020-06-18 16:41       ` Steven Rostedt
2020-06-18 17:58         ` Jann Horn
2020-06-18 17:58           ` Jann Horn
2020-06-18  9:13 ` kernel test robot
2020-06-18 10:06 ` kernel test robot

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200617183628.3594271d@oasis.local.home \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.