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SubjectRe: [PATCH 1/2] livepatch: fix non-static warnings
On Fri, Dec 14, 2018 at 04:34:23PM -0500, Joe Lawrence wrote:
> On 12/14/2018 11:56 AM, Nicholas Mc Guire wrote:
> > Sparse reported warnings about non-static symbols. For the variables a
> > simple static attribute is fine - for those symbols referenced by
> > livepatch via klp_func the symbol-names must be unmodified in the
> > relocation table - to resolve this the __noclone attribute (as
> ^^^^^^^^^^
> nit: symbol table

that should have been relocation section as described in
Documentation/livepatch/module-elf-format.txt - atleast that is how
I currently undderstand the livepatch mechanism and its seperate
relocation section.

>
> > suggested by Joe Lawrence <joe.lawrence@redhat.com>) is used
> > for the statically declared functions.
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> > Link: https://lkml.org/lkml/2018/12/13/827
> > ---
> >
> > sparse reported the following warnings:
> >
> > CHECK samples/livepatch/livepatch-shadow-fix1.c
> > samples/livepatch/livepatch-shadow-fix1.c:74:14: warning: symbol
> > 'livepatch_fix1_dummy alloc' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-fix1.c:116:6: warning: symbol
> > 'livepatch_fix1_dummy free' was not declared. Should it be static?
> >
> > CHECK samples/livepatch/livepatch-shadow-mod.c
> > samples/livepatch/livepatch-shadow-mod.c:99:1: warning: symbol
> > 'dummy_list' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:100:1: warning: symbol
> > 'dummy_list_mutex' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:107:23: warning: symbol
> > 'dummy_alloc' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:132:15: warning: symbol
> > 'dummy_free' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:140:15: warning: symbol
> > 'dummy_check' was not declared. Should it be static?
> >
> > Patch was compile tested with: x86_64_defconfig + FTRACE=y
> > FUNCTION_TRACER=y, EXPERT=y, LATENCYTOP=y, SAMPLES=y,
> > SAMPLE_LIVEPATCH=y
> >
> > Patch was runtested on an Intel i3 with:
> > insmod samples/livepatch/livepatch-shadow-mod.ko
> > insmod samples/livepatch/livepatch-shadow-fix1.ko
> > insmod samples/livepatch/livepatch-shadow-fix2.ko
> > echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
> > echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
> > rmmod livepatch-shadow-fix2
> > rmmod livepatch-shadow-fix1
> > rmmod livepatch-shadow-mod
> > and dmesg output checked.
> >
> > Patch is against 4.20-rc6 (localversion-next is next-20181214)
>
> Great testing notes, thanks for including these!
>
> > samples/livepatch/livepatch-shadow-fix1.c | 4 ++--
> > samples/livepatch/livepatch-shadow-mod.c | 16 +++++++++++-----
> > 2 files changed, 13 insertions(+), 7 deletions(-)
>
> Almost. We should only need to annotate with __noclone for those
> function definitions which the samples will be patching. As the commit
> message says, these correlate to klp_func.old_name functions found in
> klp_object.name objects (.ko modules or NULL for vmlinux).
>
> For the functions defined in samples/livepatch/*.c those would be:
>
> livepatch-callbacks-busymod.c :: busymod_work_func()
> livepatch-shadow-mod.c :: dummy_alloc()
> livepatch-shadow-mod.c :: dummy_free()
> livepatch-shadow-mod.c :: dummy_check()
>
> So even though livepatch-shadow-fix2 further refines
> livepatch-shadow-fix1, the livepatch core is going to redirect the
> original dummy_*() calls defined by livepatch-shadow-mod.c in both fix1
> and fix2 cases. Ie, the fixes modules aren't patched, only the original.
>

thanks for your patience - so I did not yet understand how this really
works together - will give it a rerun and repost a hopefully proper
solution.

thx!
hofrat

> >
> > diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> > index 49b1355..eaab10f 100644
> > --- a/samples/livepatch/livepatch-shadow-fix1.c
> > +++ b/samples/livepatch/livepatch-shadow-fix1.c
> > @@ -71,7 +71,7 @@ static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
> > return 0;
> > }
> >
> > -struct dummy *livepatch_fix1_dummy_alloc(void)
> > +static __noclone struct dummy *livepatch_fix1_dummy_alloc(void)
> > {
> > struct dummy *d;
> > void *leak;
> > @@ -108,7 +108,7 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
> > __func__, d, *shadow_leak);
> > }
> >
> > -void livepatch_fix1_dummy_free(struct dummy *d)
> > +static __noclone void livepatch_fix1_dummy_free(struct dummy *d)
> > {
> > void **shadow_leak;
> >
> > diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> > index 4c54b25..0a72bc2 100644
> > --- a/samples/livepatch/livepatch-shadow-mod.c
> > +++ b/samples/livepatch/livepatch-shadow-mod.c
> > @@ -30,6 +30,11 @@
> > * memory leak, please load these modules at your own risk -- some
> > * amount of memory may leaked before the bug is patched.
> > *
> > + * NOTE - the __noclone attribute to those functions that are to be
> > + * shared with other modules while being declared static. As livepatch
> > + * needs the unmodified symbol names and the usual "static" would
> > + * invoke gccs cloning mechanism that renames the functions this
> > + * needs to be suppressed with the additional __noclone attribute.
>
> I like the idea of providing the sample code reader this information,
> but since the compiler might also optimize livepatch-callbacks-busymod.c
> :: busymod_work_func(), it too should be annotated __noclone. Would
> that file deserve a similar comment?
>
> I don't have a strong opinion, but would throw my vote at leaving this
> in the commit message only.
>
>
> BTW, Petr/Miroslav/Josh, should we be annotating the selftests in
> similar fashion?
>
> > [ ... snip ... ]
>
> Thanks for working on this,
>
> -- Joe

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