Messages in this thread | | | Date | Fri, 16 Apr 2021 23:18:55 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 05/15] x86: Implement function_nocfi |
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On Fri, Apr 16, 2021 at 01:38:34PM -0700, Sami Tolvanen wrote: > With CONFIG_CFI_CLANG, the compiler replaces function addresses in > instrumented C code with jump table addresses. This change implements > the function_nocfi() macro, which returns the actual function address > instead. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > arch/x86/include/asm/page.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h > index 7555b48803a8..5499a05c44fc 100644 > --- a/arch/x86/include/asm/page.h > +++ b/arch/x86/include/asm/page.h > @@ -71,6 +71,20 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr, > extern bool __virt_addr_valid(unsigned long kaddr); > #define virt_addr_valid(kaddr) __virt_addr_valid((unsigned long) (kaddr)) > > +#ifdef CONFIG_CFI_CLANG
Almost every patch is talking about this magical config symbol but it is nowhere to be found. How do I disable it, is there a Kconfig entry somewhere, etc, etc?
> +/* > + * With CONFIG_CFI_CLANG, the compiler replaces function address > + * references with the address of the function's CFI jump table > + * entry. The function_nocfi macro always returns the address of the > + * actual function instead. > + */ > +#define function_nocfi(x) ({ \ > + void *addr; \ > + asm("leaq " __stringify(x) "(%%rip), %0\n\t" : "=r" (addr)); \ > + addr; \ > +})
Also, eww.
It seems all these newfangled things we get, mean obfuscating code even more. What's wrong with using __nocfi instead? That's nicely out of the way so slap that in front of functions.
Also, did you even build this on, say, 32-bit allmodconfig?
Oh well.
In file included from ./include/linux/ftrace.h:22:0, from ./include/linux/init_task.h:9, from init/init_task.c:2: ./include/linux/ftrace.h: In function ‘ftrace_init_nop’: ./arch/x86/include/asm/ftrace.h:9:40: error: implicit declaration of function ‘function_nocfi’ [-Werror=implicit-function-declaration] # define MCOUNT_ADDR ((unsigned long)(function_nocfi(__fentry__))) ^ ./include/linux/ftrace.h:671:35: note: in expansion of macro ‘MCOUNT_ADDR’ return ftrace_make_nop(mod, rec, MCOUNT_ADDR); ^~~~~~~~~~~ In file included from ./include/linux/ftrace.h:22:0, from ./include/linux/perf_event.h:49, from ./include/linux/trace_events.h:10, from ./include/trace/syscall.h:7, from ./include/linux/syscalls.h:85, from init/main.c:21: ./include/linux/ftrace.h: In function ‘ftrace_init_nop’: ./arch/x86/include/asm/ftrace.h:9:40: error: implicit declaration of function ‘function_nocfi’ [-Werror=implicit-function-declaration] # define MCOUNT_ADDR ((unsigned long)(function_nocfi(__fentry__))) ^ ./include/linux/ftrace.h:671:35: note: in expansion of macro ‘MCOUNT_ADDR’ return ftrace_make_nop(mod, rec, MCOUNT_ADDR); ^~~~~~~~~~~ In file included from ./include/linux/ftrace.h:22:0, from ./include/linux/perf_event.h:49, from ./include/linux/trace_events.h:10, from ./include/trace/syscall.h:7, from ./include/linux/syscalls.h:85, from init/initramfs.c:10: ./include/linux/ftrace.h: In function ‘ftrace_init_nop’: ./arch/x86/include/asm/ftrace.h:9:40: error: implicit declaration of function ‘function_nocfi’ [-Werror=implicit-function-declaration] # define MCOUNT_ADDR ((unsigned long)(function_nocfi(__fentry__))) ^ ./include/linux/ftrace.h:671:35: note: in expansion of macro ‘MCOUNT_ADDR’ return ftrace_make_nop(mod, rec, MCOUNT_ADDR); ^~~~~~~~~~~ In file included from ./include/linux/ftrace.h:22:0, from ./include/linux/perf_event.h:49, from arch/x86/events/core.c:15: ./include/linux/ftrace.h: In function ‘ftrace_init_nop’: ./arch/x86/include/asm/ftrace.h:9:40: error: implicit declaration of function ‘function_nocfi’ [-Werror=implicit-function-declaration] # define MCOUNT_ADDR ((unsigned long)(function_nocfi(__fentry__))) ...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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