Messages in this thread | | | Date | Fri, 12 Aug 2016 15:36:29 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v3 50/51] x86/mm: move arch_within_stack_frames() to usercopy.c |
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On Fri, Aug 12, 2016 at 01:06:41PM -0700, Kees Cook wrote: > On Fri, Aug 12, 2016 at 12:12 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > On Fri, Aug 12, 2016 at 10:36:21AM -0700, Kees Cook wrote: > >> On Fri, Aug 12, 2016 at 7:29 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > >> > When I tried to port arch_within_stack_frames() to use the new unwinder, > >> > I got a nightmare include file "header soup" scenario when unwind.h was > >> > included from thread_info.h. And anyway, I think thread_info.h isn't > >> > really an appropriate place for this function. So move it to usercopy.c > >> > instead. > >> > > >> > Since it relies on its parent's stack pointer, and the function is no > >> > longer inlined, the arguments to the __builtin_frame_address() calls > >> > have been incremented. > >> > >> Cool, looks good (minor change noted below). This patch might be a > >> good place to drop this from mm/Makefile too: > >> > >> # Since __builtin_frame_address does work as used, disable the warning. > >> CFLAGS_usercopy.o += $(call cc-disable-warning, frame-address) > >> > >> Since frame-address warnings have been disabled globally now since > >> commit 124a3d88fa20 ("Disable "frame-address" warning"). > > > > Ok, I'll do that with the next patch (51/51) which removes the > > __builtin_frame_address() calls. > > > >> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > >> > --- > >> > arch/x86/include/asm/thread_info.h | 46 ++++++++------------------------------ > >> > arch/x86/lib/usercopy.c | 43 +++++++++++++++++++++++++++++++++++ > >> > 2 files changed, 52 insertions(+), 37 deletions(-) > >> > > >> > diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h > >> > index 8b7c8d8e..fd849e6 100644 > >> > --- a/arch/x86/include/asm/thread_info.h > >> > +++ b/arch/x86/include/asm/thread_info.h > >> > @@ -176,49 +176,21 @@ static inline unsigned long current_stack_pointer(void) > >> > return sp; > >> > } > >> > > >> > -/* > >> > - * Walks up the stack frames to make sure that the specified object is > >> > - * entirely contained by a single stack frame. > >> > - * > >> > - * Returns: > >> > - * 1 if within a frame > >> > - * -1 if placed across a frame boundary (or outside stack) > >> > - * 0 unable to determine (no frame pointers, etc) > >> > - */ > >> > +#ifdef CONFIG_HARDENED_USERCOPY > >> > >> This ifdef shouldn't be needed: the arch_within_stack_frames wasn't > >> designed to depend on it. > >> > >> > +#ifdef CONFIG_FRAME_POINTER > >> > +int arch_within_stack_frames(const void * const stack, > >> > + const void * const stackend, > >> > + const void *obj, unsigned long len); > >> > +#else > >> > static inline int arch_within_stack_frames(const void * const stack, > >> > const void * const stackend, > >> > const void *obj, unsigned long len) > >> > { > >> > -#if defined(CONFIG_FRAME_POINTER) > >> > - const void *frame = NULL; > >> > - const void *oldframe; > >> > - > >> > - oldframe = __builtin_frame_address(1); > >> > - if (oldframe) > >> > - frame = __builtin_frame_address(2); > >> > - /* > >> > - * low ----------------------------------------------> high > >> > - * [saved bp][saved ip][args][local vars][saved bp][saved ip] > >> > - * ^----------------^ > >> > - * allow copies only within here > >> > - */ > >> > - while (stack <= frame && frame < stackend) { > >> > - /* > >> > - * If obj + len extends past the last frame, this > >> > - * check won't pass and the next frame will be 0, > >> > - * causing us to bail out and correctly report > >> > - * the copy as invalid. > >> > - */ > >> > - if (obj + len <= frame) > >> > - return obj >= oldframe + 2 * sizeof(void *) ? 1 : -1; > >> > - oldframe = frame; > >> > - frame = *(const void * const *)frame; > >> > - } > >> > - return -1; > >> > -#else > >> > return 0; > >> > -#endif > >> > } > >> > +#endif /* CONFIG_FRAME_POINTER */ > >> > +#endif /* CONFIG_HARDENED_USERCOPY */ > >> > + > >> > > >> > #else /* !__ASSEMBLY__ */ > >> > > >> > diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c > >> > index b490878..96ce151 100644 > >> > --- a/arch/x86/lib/usercopy.c > >> > +++ b/arch/x86/lib/usercopy.c > >> > @@ -9,6 +9,7 @@ > >> > > >> > #include <asm/word-at-a-time.h> > >> > #include <linux/sched.h> > >> > +#include <asm/unwind.h> > >> > > >> > /* > >> > * We rely on the nested NMI work to allow atomic faults from the NMI path; the > >> > @@ -34,3 +35,45 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n) > >> > return ret; > >> > } > >> > EXPORT_SYMBOL_GPL(copy_from_user_nmi); > >> > + > >> > +#ifdef CONFIG_HARDENED_USERCOPY > >> > >> Same thing: no need to check CONFIG_HARDENED_USERCOPY here: it should > >> be checking CONFIG_FRAME_POINTER instead. > > > > Now that this function is no longer inlined and is instead compiled in > > its own .c file, I was thinking that the tinyconfig folks would > > appreciate not growing the text size if there's no reason to do so. > > Keeping this #ifdef won't break anything, right? > > Hrm, well, I guess not, but it means if anyone else wants to use it > they have to remove the ifdef. I guess I don't object that much. :P
Ah. Do you expect other uses for it?
> > Also I moved the CONFIG_FRAME_POINTER check to the header file so it > > doesn't pollute the .c code. > > Right, but if FRAME_POINTER=n and HARDENED_USERCOPY=y you'll get a > build error about it being both in the .h and the .c file, if I'm > reading that correctly.
Oh, right.
-- Josh
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