From: Maxim Mikityanskiy <maxtram95@gmail.com>
To: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Mykola Lysenko <mykolal@fb.com>,
Shuah Khan <shuah@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Jesper Dangaard Brouer <hawk@kernel.org>,
bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
netdev@vger.kernel.org, Maxim Mikityanskiy <maxim@isovalent.com>
Subject: Re: [PATCH bpf-next 01/15] selftests/bpf: Fix the u64_offset_to_skb_data test
Date: Tue, 26 Dec 2023 12:38:06 +0200 [thread overview]
Message-ID: <ZYqtDuhpbS1ltM2Q@mail.gmail.com> (raw)
In-Reply-To: <w7xg34uqlrnbb3o3rspng6y563astp3hkfxjtz3xp32rqr4a42@xgpeu7qevatg>
On Tue, 26 Dec 2023 at 17:52:56 +0800, Shung-Hsi Yu wrote:
> On Wed, Dec 20, 2023 at 11:39:59PM +0200, Maxim Mikityanskiy wrote:
> > From: Maxim Mikityanskiy <maxim@isovalent.com>
> >
> > The u64_offset_to_skb_data test is supposed to make a 64-bit fill, but
> > instead makes a 16-bit one. Fix the test according to its intention. The
> > 16-bit fill is covered by u16_offset_to_skb_data.
>
> Cover letter mentioned
>
> Patch 1 (Maxim): Fix for an existing test, it will matter later in the
> series.
>
> However no subsequent patch touch upon u64_offset_to_skb_data(). Was the
> followup missing from this series?
Thanks for your vigilance, but it's actually correct, sorry for not
making it clear enough. In patch 11 ("bpf: Preserve boundaries and track
scalars on narrowing fill") I modify u16_offset_to_skb_data, because it
becomes a valid pattern after that change. If I didn't change and fix
u64_offset_to_skb_data here, I'd need to modify it in patch 11 as well
(that's what I meant when I said "it will matter later in the series",
it's indeed subtle and implicit, now that I look at it), because it
would also start passing, however, that's not what we want, because:
1. Both tests would essentially test the same thing: a 16-bit fill after
a 32-bit spill.
2. The description of u64_offset_to_skb_data clearly says: "Refill as
u64". It's a typo in the code, u16->u64 makes sense, because we spill
two u32s and fill them as a single u64.
So, this patch essentially prevents wrong changes in a further patch.
> > Signed-off-by: Maxim Mikityanskiy <maxim@isovalent.com>
> > [...]
> > SEC("tc")
> > __description("Spill u32 const scalars. Refill as u64. Offset to skb->data")
> > -__failure __msg("invalid access to packet")
> > +__failure __msg("math between pkt pointer and register with unbounded min value is not allowed")
> > __naked void u64_offset_to_skb_data(void)
> > {
> > asm volatile (" \
> > @@ -253,7 +253,7 @@ __naked void u64_offset_to_skb_data(void)
> > w7 = 20; \
> > *(u32*)(r10 - 4) = r6; \
> > *(u32*)(r10 - 8) = r7; \
> > - r4 = *(u16*)(r10 - 8); \
> > + r4 = *(u64*)(r10 - 8); \
> > r0 = r2; \
> > /* r0 += r4 R0=pkt R2=pkt R3=pkt_end R4=umax=65535 */\
> > r0 += r4; \
next prev parent reply other threads:[~2023-12-26 10:38 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 21:39 [PATCH bpf-next 00/15] Improvements for tracking scalars in the BPF verifier Maxim Mikityanskiy
2023-12-20 21:39 ` [PATCH bpf-next 01/15] selftests/bpf: Fix the u64_offset_to_skb_data test Maxim Mikityanskiy
2023-12-26 9:52 ` Shung-Hsi Yu
2023-12-26 10:38 ` Maxim Mikityanskiy [this message]
2023-12-26 13:22 ` Shung-Hsi Yu
2023-12-20 21:40 ` [PATCH bpf-next 02/15] bpf: make infinite loop detection in is_state_visited() exact Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 03/15] selftests/bpf: check if imprecise stack spills confuse infinite loop detection Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 04/15] bpf: Make bpf_for_each_spilled_reg consider narrow spills Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 05/15] selftests/bpf: Add a test case for 32-bit spill tracking Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 06/15] bpf: Add the assign_scalar_id_before_mov function Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 07/15] bpf: Add the get_reg_width function Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 08/15] bpf: Assign ID to scalars on spill Maxim Mikityanskiy
2023-12-25 3:15 ` Alexei Starovoitov
2023-12-25 21:11 ` Maxim Mikityanskiy
2023-12-25 21:26 ` Alexei Starovoitov
2023-12-20 21:40 ` [PATCH bpf-next 09/15] selftests/bpf: Test assigning " Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 10/15] bpf: Track spilled unbounded scalars Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 11/15] selftests/bpf: Test tracking " Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 12/15] bpf: Preserve boundaries and track scalars on narrowing fill Maxim Mikityanskiy
2023-12-26 5:29 ` Shung-Hsi Yu
[not found] ` <a4c8b7b9f03ff3455fbf430862b370abe9337bc9.camel@gmail.com>
2024-01-05 17:48 ` Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 13/15] selftests/bpf: Add test cases for " Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 14/15] bpf: Optimize state pruning for spilled scalars Maxim Mikityanskiy
2023-12-20 21:40 ` [PATCH bpf-next 15/15] selftests/bpf: states pruning checks for scalar vs STACK_{MISC,ZERO} Maxim Mikityanskiy
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