Messages in this thread | | | From | jarmo.tiitto@gmail ... | Subject | Re: [PATCH 1/1] pgo: Fix allocate_node() handling of non-vmlinux nodes. | Date | Wed, 02 Jun 2021 21:52:49 +0300 |
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Kees Cook wrote keskiviikkona 2. kesäkuuta 2021 20.41.28 EEST: > On Wed, Jun 02, 2021 at 03:57:04AM +0300, Jarmo Tiitto wrote: > > Currently allocate_node() will reserve nodes even if *p > > doesn't point into __llvm_prf_data_start - __llvm_prf_data_end > > range. > > > > Fix it by checking if p points into vmlinux range > > and otherwise return NULL. > > > > Signed-off-by: Jarmo Tiitto <jarmo.tiitto@gmail.com> > > --- > > kernel/pgo/instrument.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c > > index 0e07ee1b17d9..9bca535dfa91 100644 > > --- a/kernel/pgo/instrument.c > > +++ b/kernel/pgo/instrument.c > > @@ -55,6 +55,10 @@ void prf_unlock(unsigned long flags) > > static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p, > > u32 index, u64 value) > > { > > + /* check if p points into vmlinux. If not, don't allocate. */ > > + if (p < __llvm_prf_data_start || p >= __llvm_prf_data_end) > > + return NULL; > > This should be a tighter check (struct llvm_prf_data has size, so just > checking for p < __llvm_prf_data_end isn't sufficient. I recommend using > the memory_contains() helper. > > And I think this should be louder as it's entirely unexpected right > now. Perhaps: > > if (WARN_ON_ONCE(!memory_contains(__llvm_prf_data_start, > __llvm_prf_data_end, > p, sizeof(*p)))) > return NULL; > > > + > > if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end) > > return NULL; /* Out of nodes */ > > > > -- > > 2.31.1 > > > > -- > Kees Cook >
Well, if you do that the WARN_ON_ONCE() will always trigger, unless CONFIG_MODULES=n 😇
This is because 'struct llvm_prf_data *p' argument is expected (at least I think so) to point into __llvm_prf_data section in vmlinux and also into each module's own __llvm_prf_data section.
So in the end the compiler supplied pointer is likely correct, but the current v9 PGO patch attempts to reserve all vnodes from vmlinux __llvm_prf_vnds section, instead of respective module section.
I think it would be normal to ignore pointers here, until my module PGO machinery is ready.
But I agree on using memory_contains() for checking if p is within bounds. I will follow on with v2 of this patch. :-)
-Jarmo
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