On Thu, Apr 6, 2023 at 1:55 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Wed, Apr 5, 2023 at 5:40 PM Daniel Rosenberg <drosen@xxxxxxxxxx> wrote: > > > > This allows using memory retrieved from dynptrs with helper functions > > that accept ARG_PTR_TO_MEM. For instance, results from bpf_dynptr_data > > can be passed along to bpf_strncmp. > > > > Signed-off-by: Daniel Rosenberg <drosen@xxxxxxxxxx> > > --- > > I think patches like this should be targeted against bpf-next, so for > next revision please send them against bpf-next tree. > > > kernel/bpf/verifier.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 56f569811f70..20beab52812a 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -7164,12 +7164,16 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > * ARG_PTR_TO_MEM + MAYBE_NULL is compatible with PTR_TO_MEM and PTR_TO_MEM + MAYBE_NULL, > > * but ARG_PTR_TO_MEM is compatible only with PTR_TO_MEM but NOT with PTR_TO_MEM + MAYBE_NULL > > * > > + * ARG_PTR_TO_MEM is compatible with PTR_TO_MEM that is tagged with a dynptr type. > > + * > > * Therefore we fold these flags depending on the arg_type before comparison. > > */ > > if (arg_type & MEM_RDONLY) > > type &= ~MEM_RDONLY; > > if (arg_type & PTR_MAYBE_NULL) > > type &= ~PTR_MAYBE_NULL; > > + if (base_type(arg_type) == ARG_PTR_TO_MEM) > > + type &= ~DYNPTR_TYPE_FLAG_MASK; > > Something feels off here. Can you paste a bit of verifier log for the > failure you were getting. And let's have a selftest for this situation > as well. > > ARG_PTR_TO_MEM shouldn't be qualified with the DYNPTR_TYPE flag, it's > just memory, there is no need to know what type of dynptr it was > derived from. So if that happens, the problem is somewhere else. Let's > root cause and fix that. Having a selftest that demonstrates the > problem will help with that. +1 All of the DYNPTR_TYPE_FLAG_MASK flags cannot appear in type == reg->type here. They are either dynamic flags inside bpf_dynptr_kern->size or in arg_type. Like in bpf_dynptr_from_mem_proto.
