lkml.org 
[lkml]   [2022]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 04/29] x86/livepatch: Validate __fentry__ location
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

\
 
 \ /
  Last update: 2022-02-23 11:22    [W:0.214 / U:2.932 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site