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Message-ID: <ZYqtDuhpbS1ltM2Q@mail.gmail.com> Date: Tue, 26 Dec 2023 12:38:06 +0200 From: Maxim Mikityanskiy <maxtram95@...il.com> To: Shung-Hsi Yu <shung-hsi.yu@...e.com> Cc: Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, John Fastabend <john.fastabend@...il.com>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, netdev@...r.kernel.org, Maxim Mikityanskiy <maxim@...valent.com> Subject: Re: [PATCH bpf-next 01/15] selftests/bpf: Fix the u64_offset_to_skb_data test 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@...valent.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@...valent.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; \
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