On Mon, 25 Jul 2022 at 11:52, Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote: > > > From: Kumar Kartikeya Dwivedi [mailto:memxor@xxxxxxxxx] > > Sent: Thursday, July 21, 2022 3:43 PM > > Teach the verifier to detect a new KF_TRUSTED_ARGS kfunc flag, which > > means each pointer argument must be trusted, which we define as a > > pointer that is referenced (has non-zero ref_obj_id) and also needs to > > have its offset unchanged, similar to how release functions expect their > > argument. This allows a kfunc to receive pointer arguments unchanged > > from the result of the acquire kfunc. > > > > This is required to ensure that kfunc that operate on some object only > > work on acquired pointers and not normal PTR_TO_BTF_ID with same type > > which can be obtained by pointer walking. The restrictions applied to > > release arguments also apply to trusted arguments. This implies that > > strict type matching (not deducing type by recursively following members > > at offset) and OBJ_RELEASE offset checks (ensuring they are zero) are > > used for trusted pointer arguments. > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> > > --- > > include/linux/btf.h | 32 ++++++++++++++++++++++++++++++++ > > kernel/bpf/btf.c | 17 ++++++++++++++--- > > net/bpf/test_run.c | 5 +++++ > > 3 files changed, 51 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/btf.h b/include/linux/btf.h > > index 6dfc6eaf7f8c..cb63aa71e82f 100644 > > --- a/include/linux/btf.h > > +++ b/include/linux/btf.h > > @@ -17,6 +17,38 @@ > > #define KF_RELEASE (1 << 1) /* kfunc is a release function */ > > #define KF_RET_NULL (1 << 2) /* kfunc returns a pointer that may be NULL */ > > #define KF_KPTR_GET (1 << 3) /* kfunc returns reference to a kptr */ > > +/* Trusted arguments are those which are meant to be referenced arguments > > with > > + * unchanged offset. It is used to enforce that pointers obtained from acquire > > + * kfuncs remain unmodified when being passed to helpers taking trusted args. > > + * > > + * Consider > > + * struct foo { > > + * int data; > > + * struct foo *next; > > + * }; > > + * > > + * struct bar { > > + * int data; > > + * struct foo f; > > + * }; > > + * > > + * struct foo *f = alloc_foo(); // Acquire kfunc > > + * struct bar *b = alloc_bar(); // Acquire kfunc > > + * > > + * If a kfunc set_foo_data() wants to operate only on the allocated object, it > > + * will set the KF_TRUSTED_ARGS flag, which will prevent unsafe usage like: > > + * > > + * set_foo_data(f, 42); // Allowed > > + * set_foo_data(f->next, 42); // Rejected, non-referenced pointer > > + * set_foo_data(&f->next, 42);// Rejected, referenced, but bad offset > > + * set_foo_data(&b->f, 42); // Rejected, referenced, but wrong type > > + * > > + * In the final case, usually for the purposes of type matching, it is deduced > > + * by looking at the type of the member at the offset, but due to the > > + * requirement of trusted argument, this deduction will be strict and not done > > + * for this case. > > + */ > > +#define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer > > arguments */ > > Hi Kumar > > would it make sense to introduce per-parameter flags? I have a function > that has several parameters, but only one is referenced. > I have a patch for that in my local branch, I can fix it up and post it. But first, can you give an example of where you think you need it? > Thanks > > Roberto
