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To: Saket Kumar Bhaskar , Alexei Starovoitov CC: bpf , Network Development , "open list:KERNEL SELFTEST FRAMEWORK" , LKML , Alexei Starovoitov , "Hari Bathini" , Andrii Nakryiko , "Daniel Borkmann" , "David S. Miller" , Jakub Kicinski , Jesper Dangaard Brouer , Martin KaFai Lau , Eddy Z , "Eric Dumazet" , Paolo Abeni , Simon Horman , Song Liu , Yonghong Song , John Fastabend , "KP Singh" References: <20250122183720.1411176-1-skb99@linux.ibm.com> <332c50f5-3c68-4fce-8bb3-161f76f2119c@intel.com> From: Alexander Lobakin Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MI2P293CA0012.ITAP293.PROD.OUTLOOK.COM (2603:10a6:290:45::10) To DS0PR11MB8718.namprd11.prod.outlook.com (2603:10b6:8:1b9::20) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB8718:EE_|DM4PR11MB8159:EE_ X-MS-Office365-Filtering-Correlation-Id: 4f37f6c1-ca2d-43e5-4654-08dd451a3434 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014|7053199007; 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This discrepancy led to an overflow when >>>> bpf_xdp_frags_increase_tail() checked for tailroom, as skb_frag_size(frag) >>>> could be greater than rxq->frag_size (when PAGE_SIZE > 4096). >>>> >>>> This commit updates the page size references to 4096 to ensure consistency >>>> and prevent overflow issues in fragment size calculations. >>> >>> This isn't right. Please fix the selftest instead. >> >> It's not _that_ easy, I had tried in the past. Anyway, this patch is >> *not* a good "solution". >> >> If you (Saket) really want to fix this, both test_run and the selftest >> must be in sync, so you need to (both are arch-dependent): 1) get the >> correct PAGE_SIZE; 2) calculate the correct tailroom in userspace (which >> depends on sizeof(shinfo) and SKB_DATA_ALIGN -> SMP_CACHE_BYTES). >> >>> >>> pw-bot: cr >> >> Thanks, >> Olek > There is a mixup in kernel b/w 4096 and PAGE_SIZE and all selftest seem > to be based on 4096 as the size, so I changed the PAGE_SIZE to 4096, > but if we have to use PAGE_SIZE we need this change in kernel. I know how it is done, I was working on adjacent code, that's why I spoke up and told you what you need to account if you want to fix this properly. xdp->frame_sz is hard buffer len, usually in range [PAGE_SIZE / 2, PAGE_SIZE], and it includes: headroom (XDP_PACKET_HEADROOM + some drivers reserve NET_IP_ALIGN) actual data buffer tailroom (SKB_DATA_ALIGN(sizeof(skb_shared_info))) So to determine the actual data buffer size, you need to: * know PAGE_SIZE * know headroom * know tailroom Hardcoding anything from the list will lead to selftest fails. > In place of PAGE_SIZE 4096 was used here: > > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > index 501ec4249..6b7fddfbb 100644 > --- a/net/bpf/test_run.c > +++ b/net/bpf/test_run.c > @@ -1251,7 +1251,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, > headroom -= ctx->data; > } > > - max_data_sz = 4096 - headroom - tailroom; > + max_data_sz = PAGE_SIZE - headroom - tailroom; > if (size > max_data_sz) { > /* disallow live data mode for jumbo frames */ > if (do_live) > > Assuming that change in kernel we should also update the selftest to > 64K page size for ppc64: > > diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_adjust_tail.c b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_tail.c > index 53d6ad8c2..037142e21 100644 > --- a/tools/testing/selftests/bpf/prog_tests/xdp_adjust_tail.c > +++ b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_tail.c > @@ -226,7 +226,7 @@ static void test_xdp_adjust_frags_tail_grow(void) > > prog_fd = bpf_program__fd(prog); > > - buf = malloc(16384); > + buf = malloc(262144); > if (!ASSERT_OK_PTR(buf, "alloc buf 16Kb")) > goto out; > > @@ -254,12 +254,12 @@ static void test_xdp_adjust_frags_tail_grow(void) > ASSERT_EQ(buf[i], 1, "9Kb+10b-untouched"); > > /* Test a too large grow */ > - memset(buf, 1, 16384); > - exp_size = 9001; > + memset(buf, 1, 262144); > + exp_size = 132001; > > topts.data_in = topts.data_out = buf; > - topts.data_size_in = 9001; > - topts.data_size_out = 16384; > + topts.data_size_in = 132001; > + topts.data_size_out = 262144; > err = bpf_prog_test_run_opts(prog_fd, &topts); > > ASSERT_OK(err, "9Kb+10b"); > > diff --git a/tools/testing/selftests/bpf/progs/test_xdp_adjust_tail_grow.c b/tools/testing/selftests/bpf/progs/test_xdp_adjust_tail_grow.c > index 81bb38d72..40a0c5469 100644 > --- a/tools/testing/selftests/bpf/progs/test_xdp_adjust_tail_grow.c > +++ b/tools/testing/selftests/bpf/progs/test_xdp_adjust_tail_grow.c > @@ -27,8 +27,8 @@ int _xdp_adjust_tail_grow(struct xdp_md *xdp) > offset = 4096 - 256 - tailroom - data_len; > } else if (data_len == 9000) { > offset = 10; > - } else if (data_len == 9001) { > - offset = 4096; > + } else if (data_len == 132001) { > + offset = 65536; > } else { > return XDP_ABORTED; /* No matching test */ > } > > The above change is intended for feedback. The date_len and other > values in the test cases can be adjusted to be based on the page > size, rather than being hard-coded, to ensure compatibility with > different page sizes. In the code above I only see one hardcode replaced with another one. Note that PAGE_SIZE == 4096 was hardcoded to be able to run selftests on x86_64 in the first place. If you want to enable them on non-fixed-page-size arches, then I mentioned 2 times already what you need to do. > > Thanks, > Saket Thanks, Olek