Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 26 Aug 2009 10:47:13 +0200 | From | Ingo Molnar <> | Subject | Re: [kmemcheck] WARNING: kmemcheck: Caught 32-bit read from uninitialized memory, in sock_init_data() |
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* Vegard Nossum <vegard.nossum@gmail.com> wrote:
> 2009/8/26 Ingo Molnar <mingo@elte.hu>: > > > > * Eric Dumazet <eric.dumazet@gmail.com> wrote: > > > >> Vegard Nossum a ??crit : > >> > 2009/8/26 Ingo Molnar <mingo@elte.hu>: > >> >> -tip testing found another kmemcheck warning: > >> >> > >> >> calling ??netlink_proto_init+0x0/0x1b0 @ 1 > >> >> NET: Registered protocol family 16 > >> >> initcall netlink_proto_init+0x0/0x1b0 returned 0 after 39062 usecs > >> >> calling ??olpc_init+0x0/0x110 @ 1 > >> >> WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f5c38304) > >> >> 0100000002000000000000000000000000000000ad4eaddeffffffffffffffff > >> >> ??i i i i i i u u i i i i i i i i i i i i i i i i i i i i i i i i > >> >> ?? ?? ?? ?? ^ > >> >> > >> >> Pid: 1, comm: swapper Not tainted (2.6.31-rc7-tip-01170-gaaea9cf-dirty #24) P4DC6 > >> >> EIP: 0060:[<c15c8ab1>] EFLAGS: 00010286 CPU: 0 > >> >> EIP is at sock_init_data+0xe1/0x220 > >> >> EAX: 0001b000 EBX: f606196c ECX: 00000000 EDX: c1a148d2 > >> >> ESI: f6061800 EDI: f5c38300 EBP: f606ef0c ESP: c1ceb9ac > >> >> ??DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 > >> >> CR0: 8005003b CR2: f60a8108 CR3: 01a61000 CR4: 000006f0 > >> >> DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 > >> >> DR6: ffff4ff0 DR7: 00000400 > >> >> ??[<c15fac15>] __netlink_create+0x35/0xa0 > >> >> ??[<c15fd01a>] netlink_kernel_create+0x5a/0x180 > >> >> ??[<c15df55e>] rtnetlink_net_init+0x1e/0x50 > >> >> ??[<c15d130a>] register_pernet_operations+0x6a/0xf0 > >> >> ??[<c15d14fe>] register_pernet_subsys+0x1e/0x30 > >> >> ??[<c1b3d84c>] rtnetlink_init+0x4c/0x100 > >> >> ??[<c1b3e105>] netlink_proto_init+0x105/0x1b0 > >> >> ??[<c1001037>] do_one_initcall+0x27/0x170 > >> >> ??[<c1afea97>] kernel_init+0x157/0x210 > >> >> ??[<c10039a7>] kernel_thread_helper+0x7/0x10 > >> >> ??[<ffffffff>] 0xffffffff > >> >> initcall olpc_init+0x0/0x110 returned 0 after 0 usecs > >> >> calling ??bdi_class_init+0x0/0x40 @ 1 > >> >> > >> >> config attached. > >> > > >> > Thanks. AFAICT, it's this one: > >> > > >> > 1816 void sock_init_data(struct socket *sock, struct sock *sk) > >> > 1817 { > >> > ... > >> > 1835 ?? ?? ?? ?? sock_set_flag(sk, SOCK_ZAPPED); > >> > >> Are you sure it is not the 16 bit padding in 'struct sock', after 'type' field ? > >> > >> struct socket { > >> ?? ?? ?? socket_state ?? ?? ?? ??state; > >> ?? ?? ?? short ?? ?? ?? ?? ?? type; > >> // here, a 16 bits hole > >> ?? ?? ?? unsigned long ?? ?? ?? flags; > >> > >> the warning is strange since I suspect it happens here : > >> > >> ?? ?? if (sock) { > >> <<>> ??sk->sk_type = ?? sock->type; // here, kmemcheck warning while reading sock->type > >> ?? ?? ?? sk->sk_sleep ?? ??= ?? &sock->wait; > >> ?? ?? ?? sock->sk ?? ??= ?? sk; > >> > >> and sock->type is a 16 bit field, correctly initialized (with value = 2) > >> (Yes the hole, right after, is not initialized) > >> > > Ah, right, makes sense. There are just two uninitialized bytes, too, > we can see it in the shadow dump: > > >> WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f5c38304) > >> 0100000002000000000000000000000000000000ad4eaddeffffffffffffffff > >> ??i i i i i i u u i i i i i i i i i i i i i i i i i i i i i i i i > > > > if so then we could perhaps annotate that by initializing it to zero > > on kmemcheck only. (or initialize it unconditionally if possible - > > that's generally the cleanest, 16-bit accesses arent cheap on all > > platforms) > > We should have eliminated these padding-related false-positives by > droppnig the -Os / CONFIG_CC_OPTIMIZE_FOR_SIZE, which should emit > a movzwl instruction or so instead of movl, but it's admittedly > somewhat dependent on gcc anyway. I'm wondering whether it would > be worth it to (try to) patch gcc not to emit these > "bigger-than-necessary" loads with a new -fsomething flag.
The latency of even the smallest enhancements to GCC is so huge that we cannot rely on it. There's really just a few places in the kernel that are that tightly/trickily packed - the signal code (which we annotated IIRC?) and the networking code. Lets annotate it so that we can have a 'no warnings' baseline.
Ingo
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