Messages in this thread | | | Date | Fri, 18 Feb 2022 13:08:31 -0800 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 04/29] x86/livepatch: Validate __fentry__ location |
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On Fri, Feb 18, 2022 at 05:49:06PM +0100, Peter Zijlstra wrote: > Currently livepatch assumes __fentry__ lives at func+0, which is most > likely untrue with IBT on. Override the weak klp_get_ftrace_location() > function with an arch specific version that's IBT aware. > > Also make the weak fallback verify the location is an actual ftrace > location as a sanity check. > > Suggested-by: Miroslav Benes <mbenes@suse.cz> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/x86/include/asm/livepatch.h | 9 +++++++++ > kernel/livepatch/patch.c | 2 +- > 2 files changed, 10 insertions(+), 1 deletion(-) > > --- a/arch/x86/include/asm/livepatch.h > +++ b/arch/x86/include/asm/livepatch.h > @@ -17,4 +17,13 @@ static inline void klp_arch_set_pc(struc > ftrace_instruction_pointer_set(fregs, ip); > } > > +#define klp_get_ftrace_location klp_get_ftrace_location > +static inline unsigned long klp_get_ftrace_location(unsigned long faddr) > +{ > + unsigned long addr = ftrace_location(faddr); > + if (!addr && IS_ENABLED(CONFIG_X86_IBT)) > + addr = ftrace_location(faddr + 4); > + return addr;
I'm kind of surprised this logic doesn't exist in ftrace itself. Is livepatch really the only user that needs to find the fentry for a given function?
I had to do a double take for the ftrace_location() semantics, as I originally assumed that's what it did, based on its name and signature.
Instead it apparently functions like a bool but returns its argument on success.
Though the function comment tells a different story:
/** * ftrace_location - return true if the ip giving is a traced location
So it's all kinds of confusing...
-- Josh
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