From: Roberto Sassu <roberto.sassu@huawei.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Pablo Neira Ayuso" <pablo@netfilter.org>,
"Florian Westphal" <fw@strlen.de>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Lorenzo Bianconi" <lorenzo@kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"netfilter-devel@vger.kernel.org"
<netfilter-devel@vger.kernel.org>
Subject: RE: [PATCH bpf-next v7 04/13] bpf: Add support for forcing kfunc args to be trusted
Date: Tue, 26 Jul 2022 12:58:33 +0000 [thread overview]
Message-ID: <afabc18be104482ba5464817ac4f8729@huawei.com> (raw)
In-Reply-To: <CAP01T74s8E0-60ZtviLcTDR8sY3hUsAiTc2oTii_i4XeW3J2xw@mail.gmail.com>
> From: Kumar Kartikeya Dwivedi [mailto:memxor@gmail.com]
> Sent: Tuesday, July 26, 2022 2:56 PM
> On Tue, 26 Jul 2022 at 12:02, Roberto Sassu <roberto.sassu@huawei.com>
> wrote:
> >
> > > From: Kumar Kartikeya Dwivedi [mailto:memxor@gmail.com]
> > > Sent: Tuesday, July 26, 2022 11:30 AM
> > > On Mon, 25 Jul 2022 at 11:52, Roberto Sassu <roberto.sassu@huawei.com>
> > > wrote:
> > > >
> > > > > From: Kumar Kartikeya Dwivedi [mailto:memxor@gmail.com]
> > > > > 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@gmail.com>
> > > > > ---
> > > > > 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?
> >
> > I have pushed the complete patch set here, for testing:
> >
> > https://github.com/robertosassu/vmtest/tree/bpf-verify-sig-v9/travis-ci/diffs
> >
> > I rebased to bpf-next/master, and introduced KF_SLEEPABLE (similar
> > functionality of " btf: Add a new kfunc set which allows to mark
> > a function to be sleepable" from Benjamin Tissoires).
> >
> > The patch where I would use per-parameter KF_TRUSTED_ARGS is
> > number 8. I also used your new API in patch 7 and it works well.
> >
>
> Ok, looks like you'll need it for the struct key * argument as there
> are multiple pointers in the argument list and not all of them need to
> be trusted. I will clean up and post the patch with a test later today
> to the list.
Yes, thanks a lot!
Roberto
next prev parent reply other threads:[~2022-07-26 12:58 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-21 13:42 [PATCH bpf-next v7 00/13] New nf_conntrack kfuncs for insertion, changing timeout, status Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 01/13] bpf: Introduce 8-byte BTF set Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 02/13] tools/resolve_btfids: Add support for 8-byte BTF sets Kumar Kartikeya Dwivedi
2022-07-21 20:51 ` Jiri Olsa
2022-07-21 13:42 ` [PATCH bpf-next v7 03/13] bpf: Switch to new kfunc flags infrastructure Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 04/13] bpf: Add support for forcing kfunc args to be trusted Kumar Kartikeya Dwivedi
2022-07-22 4:10 ` Alexei Starovoitov
2022-07-22 10:26 ` Kumar Kartikeya Dwivedi
2022-07-25 9:52 ` Roberto Sassu
2022-07-26 9:30 ` Kumar Kartikeya Dwivedi
2022-07-26 10:02 ` Roberto Sassu
2022-07-26 12:55 ` Kumar Kartikeya Dwivedi
2022-07-26 12:58 ` Roberto Sassu [this message]
2022-07-21 13:42 ` [PATCH bpf-next v7 05/13] bpf: Add documentation for kfuncs Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 06/13] net: netfilter: Deduplicate code in bpf_{xdp,skb}_ct_lookup Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 07/13] net: netfilter: Add kfuncs to allocate and insert CT Kumar Kartikeya Dwivedi
2022-07-22 9:02 ` Pablo Neira Ayuso
2022-07-22 9:39 ` Kumar Kartikeya Dwivedi
2022-07-23 7:50 ` Pablo Neira Ayuso
2022-07-25 8:52 ` Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 08/13] net: netfilter: Add kfuncs to set and change CT timeout Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 09/13] net: netfilter: Add kfuncs to set and change CT status Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 10/13] selftests/bpf: Add verifier tests for trusted kfunc args Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 11/13] selftests/bpf: Add tests for new nf_conntrack kfuncs Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 12/13] selftests/bpf: Add negative " Kumar Kartikeya Dwivedi
2022-07-21 13:42 ` [PATCH bpf-next v7 13/13] selftests/bpf: Fix test_verifier failed test in unprivileged mode Kumar Kartikeya Dwivedi
2022-07-21 17:28 ` [PATCH bpf-next v7 00/13] New nf_conntrack kfuncs for insertion, changing timeout, status Zvi Effron
2022-07-21 18:01 ` Kumar Kartikeya Dwivedi
2022-07-22 4:10 ` patchwork-bot+netdevbpf
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