Messages in this thread | | | Date | Thu, 14 Oct 2021 13:21:38 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v5 09/15] x86: Use an opaque type for functions not callable from C |
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On Wed, Oct 13, 2021 at 11:16:52AM -0700, Sami Tolvanen wrote: > The kernel has several assembly functions that are not directly callable > from C. Use an opaque type for these function prototypes to make misuse > harder, and to avoid the need to annotate references to these functions > for Clang's Control-Flow Integrity (CFI). > > Suggested-by: Andy Lutomirski <luto@amacapital.net> > Suggested-by: Alexander Lobakin <alobakin@pm.me> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > Reviewed-by: Kees Cook <keescook@chromium.org> > Tested-by: Nick Desaulniers <ndesaulniers@google.com> > Tested-by: Sedat Dilek <sedat.dilek@gmail.com> > --- > arch/x86/include/asm/ftrace.h | 2 +- > arch/x86/include/asm/idtentry.h | 10 +++++----- > arch/x86/include/asm/page_64.h | 7 ++++--- > arch/x86/include/asm/paravirt_types.h | 3 ++- > arch/x86/include/asm/processor.h | 2 +- > arch/x86/include/asm/proto.h | 25 +++++++++++++------------ > arch/x86/include/asm/uaccess_64.h | 9 +++------ > arch/x86/kernel/alternative.c | 2 +- > arch/x86/kernel/ftrace.c | 2 +- > arch/x86/kernel/paravirt.c | 4 ++-- > arch/x86/kvm/emulate.c | 4 ++-- > arch/x86/kvm/kvm_emulate.h | 9 ++------- > arch/x86/xen/enlighten_pv.c | 6 +++--- > arch/x86/xen/xen-ops.h | 10 +++++----- > 14 files changed, 45 insertions(+), 50 deletions(-)
No matter from which direction I look at it, wrapping some functions which a crazy macro doesn't look good.
So what's the plan here?
Everytime someone adds an asm function which is not callable from C but forgets to use that magic macro, someone from team CFI will send a patch fixing that?
I.e., a whack-a-mole game?
If we're going to do that keep-CFI-working game, we might just as well not do the macro but use the C code it evaluates to, so that at least it looks ok-ish:
DECLARE_NOT_CALLED_FROM_C(int3_magic);
vs
extern const u8 int3_magic[];
(Just picked one at random).
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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