Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753387AbdI1Ohx (ORCPT ); Thu, 28 Sep 2017 10:37:53 -0400 Received: from www62.your-server.de ([213.133.104.62]:52496 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752385AbdI1Ohv (ORCPT ); Thu, 28 Sep 2017 10:37:51 -0400 Message-ID: <59CD093A.6030201@iogearbox.net> Date: Thu, 28 Sep 2017 16:37:46 +0200 From: Daniel Borkmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Mark Rutland , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, syzkaller@googlegroups.com CC: "David S. Miller" , Alexei Starovoitov , Tejun Heo , Christoph Lameter Subject: Re: EBPF-triggered WARNING at mm/percpu.c:1361 in v4-14-rc2 References: <20170928112727.GA11310@leverpostej> In-Reply-To: <20170928112727.GA11310@leverpostej> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9053 Lines: 196 On 09/28/2017 01:27 PM, Mark Rutland wrote: > Hi, > > While fuzzing v4.14-rc2 with Syzkaller, I found it was possible to trigger the > warning at mm/percpu.c:1361, on both arm64 and x86_64. This appears to require > increasing RLIMIT_MEMLOCK, so to the best of my knowledge this cannot be > triggered by an unprivileged user. > > I've included example splats for both x86_64 and arm64, along with a C > reproducer, inline below. > > It looks like dev_map_alloc() requests a percpu alloction of 32776 bytes, which > is larger than the maximum supported allocation size of 32768 bytes. > > I wonder if it would make more sense to pr_warn() for sizes that are too > large, so that callers don't have to roll their own checks against > PCPU_MIN_UNIT_SIZE? Perhaps the pr_warn() should be ratelimited; or could there be an option where we only return NULL, not triggering a warn at all (which would likely be what callers might do anyway when checking against PCPU_MIN_UNIT_SIZE and then bailing out)? > e.g. something like: > > ---- > diff --git a/mm/percpu.c b/mm/percpu.c > index 59d44d6..f731c45 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -1355,8 +1355,13 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > bits = size >> PCPU_MIN_ALLOC_SHIFT; > bit_align = align >> PCPU_MIN_ALLOC_SHIFT; > > - if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE || > - !is_power_of_2(align))) { > + if (unlikely(size > PCPU_MIN_UNIT_SIZE)) { > + pr_warn("cannot allocate pcpu chunk of size %zu (max %zu)\n", > + size, PCPU_MIN_UNIT_SIZE); > + return NULL; > + } > + > + if (unlikely(!size || align > PAGE_SIZE || !is_power_of_2(align))) { > WARN(true, "illegal size (%zu) or align (%zu) for percpu allocation\n", > size, align); > return NULL; > ---- > > Thanks, > Mark. > > > > Example splat(x86_64) > ---- > [ 138.144185] illegal size (32776) or align (8) for percpu allocation > [ 138.150452] ------------[ cut here ]------------ > [ 138.155074] WARNING: CPU: 1 PID: 2223 at mm/percpu.c:1361 pcpu_alloc+0x7c/0x5f0 > [ 138.162369] Modules linked in: > [ 138.165423] CPU: 1 PID: 2223 Comm: repro Not tainted 4.14.0-rc2 #3 > [ 138.171593] Hardware name: LENOVO 7484A3G/LENOVO, BIOS 5CKT54AUS 09/07/2009 > [ 138.178543] task: ffff881b73069980 task.stack: ffffa36f40f90000 > [ 138.184455] RIP: 0010:pcpu_alloc+0x7c/0x5f0 > [ 138.188633] RSP: 0018:ffffa36f40f93e00 EFLAGS: 00010286 > [ 138.193853] RAX: 0000000000000037 RBX: 0000000000000000 RCX: 0000000000000000 > [ 138.200974] RDX: ffff881b7ec94a40 RSI: ffff881b7ec8cbb8 RDI: ffff881b7ec8cbb8 > [ 138.208097] RBP: ffffa36f40f93e68 R08: 0000000000000001 R09: 00000000000002c4 > [ 138.215219] R10: 0000562a577047f0 R11: ffffffffa10ad7cd R12: ffff881b73216cc0 > [ 138.222343] R13: 0000000000000014 R14: 00007ffebeed0900 R15: ffffffffffffffea > [ 138.229463] FS: 00007fef84a15700(0000) GS:ffff881b7ec80000(0000) knlGS:0000000000000000 > [ 138.237538] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 138.243274] CR2: 00007fef84497ba0 CR3: 00000001b3235000 CR4: 00000000000406e0 > [ 138.250397] Call Trace: > [ 138.252844] __alloc_percpu+0x10/0x20 > [ 138.256508] dev_map_alloc+0x122/0x1b0 > [ 138.260255] SyS_bpf+0x8f9/0x10b0 > [ 138.263570] ? security_task_setrlimit+0x3e/0x60 > [ 138.268184] ? do_prlimit+0xa6/0x1f0 > [ 138.271760] entry_SYSCALL_64_fastpath+0x13/0x94 > [ 138.276372] RIP: 0033:0x7fef84546259 > [ 138.279946] RSP: 002b:00007ffebeed09b8 EFLAGS: 00000206 ORIG_RAX: 0000000000000141 > [ 138.287503] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fef84546259 > [ 138.294627] RDX: 0000000000000014 RSI: 00007ffebeed09d0 RDI: 0000000000000000 > [ 138.301749] RBP: 0000562a57704780 R08: 00007fef84810cb0 R09: 00007ffebeed0ae8 > [ 138.308874] R10: 0000562a577047f0 R11: 0000000000000206 R12: 0000562a577045d0 > [ 138.315997] R13: 00007ffebeed0ae0 R14: 0000000000000000 R15: 0000000000000000 > [ 138.323122] Code: fe 00 10 00 00 77 10 48 8b 4d b8 48 89 c8 48 83 e8 01 48 85 c1 74 1e 48 8b 55 b8 48 8b 75 c0 48 c7 c7 90 5e be a0 e8 40 88 f3 ff <0f> ff 45 31 ed e9 5e 02 00 00 4c 8b 6d c0 49 89 cc 49 c1 ec 02 > [ 138.341953] ---[ end trace b6e380365bfb8a36 ]--- > ---- > > > > Example splat (arm64) > ---- > [ 17.287365] illegal size (32776) or align (8) for percpu allocation > [ 17.295347] ------------[ cut here ]------------ > [ 17.297191] WARNING: CPU: 1 PID: 1440 at mm/percpu.c:1361 pcpu_alloc+0x120/0x9f0 > [ 17.307723] Kernel panic - not syncing: panic_on_warn set ... > [ 17.307723] > [ 17.311755] CPU: 1 PID: 1440 Comm: repro Not tainted 4.14.0-rc2-00001-gd7ad33d #115 > [ 17.320675] Hardware name: linux,dummy-virt (DT) > [ 17.323858] Call trace: > [ 17.325246] [] dump_backtrace+0x0/0x558 > [ 17.332538] [] show_stack+0x20/0x30 > [ 17.340391] [] dump_stack+0x128/0x1a0 > [ 17.342081] [] panic+0x250/0x518 > [ 17.344096] [] __warn+0x2a4/0x310 > [ 17.345654] [] report_bug+0x1d4/0x290 > [ 17.348652] [] bug_handler.part.1+0x40/0xf8 > [ 17.356873] [] bug_handler+0x4c/0x88 > [ 17.360543] [] brk_handler+0x1c4/0x360 > [ 17.365076] [] do_debug_exception+0x118/0x398 > [ 17.368297] Exception stack(0xffff80001c82b930 to 0xffff80001c82ba70) > [ 17.372981] b920: 0000000000000037 0000000000000000 > [ 17.380137] b940: bec1e481d6136f00 dfff200000000000 1fffe40001cbd30c dfff200000000000 > [ 17.384902] b960: dfff200000000000 0000000000000000 ffff80001ce6c050 1ffff000039cd809 > [ 17.392527] b980: ffff80001ce6c048 ffff80001ce6c068 1ffff000039cd80c 1ffff000039cd80e > [ 17.396935] b9a0: 1ffff000039cd80d ffff20000e1485a0 0000000000000000 0000000000000000 > [ 17.404665] b9c0: ffff20000da58140 0000000000000000 00000000014000c0 0000000000000008 > [ 17.407064] b9e0: 0000000000000004 000000000000800b 1ffff000039057b9 ffff80001c82bdcc > [ 17.415067] ba00: 0000000000000000 1ffff000039c0b14 1ffff000039c0b12 ffff80001c82ba70 > [ 17.419137] ba20: ffff20000850c880 ffff80001c82ba70 ffff20000850c880 0000000080000145 > [ 17.426052] ba40: 0000000000000008 ffff20000ae60b88 0001000000000000 00000000f4f4f404 > [ 17.437346] ba60: ffff80001c82ba70 ffff20000850c880 > [ 17.445759] [] el1_dbg+0x18/0x74 > [ 17.448272] [] pcpu_alloc+0x120/0x9f0 > [ 17.456523] [] __alloc_percpu+0x30/0x40 > [ 17.458412] [] dev_map_alloc+0x58c/0x8d8 > [ 17.462917] [] SyS_bpf+0x86c/0x2d58 > [ 17.468126] Exception stack(0xffff80001c82bec0 to 0xffff80001c82c000) > [ 17.470108] bec0: 0000000000000000 0000ffffe78f4898 0000000000000014 0000000000000000 > [ 17.474655] bee0: 0000000000000000 0000ffffe78f49f0 0000001000000000 0000001000000000 > [ 17.482196] bf00: 0000000000000118 0003ffffffffffff 0101010101010101 0000001000000000 > [ 17.486928] bf20: 0000ffffb6468030 0000000000000000 0000ffffb6468028 000000000000071c > [ 17.498389] bf40: 0000ffffb63b8a00 0000aaaaba991028 0000000000000000 0000aaaaba9808f0 > [ 17.502871] bf60: 0000000000000000 0000aaaaba980730 0000000000000000 0000000000000000 > [ 17.505879] bf80: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > [ 17.514090] bfa0: 0000000000000000 0000ffffe78f4870 0000aaaaba9808e0 0000ffffe78f4870 > [ 17.520813] bfc0: 0000ffffb63b8a24 0000000080000000 0000000000000000 0000000000000118 > [ 17.523888] bfe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > [ 17.532537] [] el0_svc_naked+0x24/0x28 > [ 17.540427] SMP: stopping secondary CPUs > [ 17.566662] Kernel Offset: disabled > [ 17.567498] CPU features: 0x002082 > [ 17.568238] Memory Limit: none > [ 17.568958] Rebooting in 86400 seconds.. > ---- > > > > C reproducer > ---- > #include > #include > #include > #include > > #include > > /* > * Debian Stretch's headers are too old to contain a number of interesting > * values, so manually define them to keep things legible... > */ > struct LOCALDEF_bpf_attr { > uint32_t map_type; > uint32_t key_size; > uint32_t value_size; > uint32_t max_entries; > uint32_t map_flags; > }; > > #define LOCALDEF_BPF_MAP_TYPE_DEVMAP 0xe > > int main(int argc, char *argv[]) > { > struct rlimit rlimit = { > .rlim_cur = 8 << 20, > .rlim_max = 8 << 20, > }; > > setrlimit(RLIMIT_MEMLOCK, &rlimit); > > struct LOCALDEF_bpf_attr attr = { > .map_type = LOCALDEF_BPF_MAP_TYPE_DEVMAP, > .key_size = 4, > .value_size = 4, > .max_entries = 0x40001, > .map_flags = 0, > }; > > syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr)); > > return 0; > } > ---- >