Messages in this thread | | | Date | Wed, 23 Feb 2022 11:21:33 +0100 (CET) | From | Miroslav Benes <> | Subject | Re: [PATCH 04/29] x86/livepatch: Validate __fentry__ location |
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On Wed, 23 Feb 2022, Peter Zijlstra wrote:
> On Fri, Feb 18, 2022 at 01:08:31PM -0800, Josh Poimboeuf wrote: > > 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... > > Yes.. so yesterday, when making function-graph tracing not explode, I > ran into a similar issue. Steve suggested something along the lines of > .... this. > > (modified from his actual suggestion to also cover this case) > > Let me go try this...
Yes, this looks good.
> --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -1578,7 +1578,23 @@ unsigned long ftrace_location_range(unsi > */ > unsigned long ftrace_location(unsigned long ip) > { > - return ftrace_location_range(ip, ip); > + struct dyn_ftrace *rec; > + unsigned long offset; > + unsigned long size; > + > + rec = lookup_rec(ip, ip); > + if (!rec) { > + if (!kallsyms_lookup(ip, &size, &offset, NULL, NULL))
Since we do not care about a symbol name, kallsyms_lookup_size_offset() would be better I think.
Miroslav
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