Messages in this thread Patch in this message | | | Date | Wed, 23 Feb 2022 11:09:44 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 04/29] x86/livepatch: Validate __fentry__ location |
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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...
--- 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)) + goto out; + + rec = lookup_rec(ip - offset, (ip - offset) + size); + } + + if (rec) + return rec->ip; + +out: + return 0; } /** @@ -5110,11 +5126,16 @@ int register_ftrace_direct(unsigned long struct ftrace_func_entry *entry; struct ftrace_hash *free_hash = NULL; struct dyn_ftrace *rec; - int ret = -EBUSY; + int ret = -ENODEV; mutex_lock(&direct_mutex); + ip = ftrace_location(ip); + if (!ip) + goto out_unlock; + /* See if there's a direct function at @ip already */ + ret = -EBUSY; if (ftrace_find_rec_direct(ip)) goto out_unlock; @@ -5222,6 +5243,10 @@ int unregister_ftrace_direct(unsigned lo mutex_lock(&direct_mutex); + ip = ftrace_location(ip); + if (!ip) + goto out_unlock; + entry = find_direct_entry(&ip, NULL); if (!entry) goto out_unlock;
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