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SubjectRe: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement fast refcount overflow protection
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On Thu, 2017-08-31 at 11:45 -0700, Kees Cook wrote:
> On Thu, Aug 31, 2017 at 10:19 AM, Mike Galbraith <efault@gmx.de> wrote:
> > On Thu, 2017-08-31 at 10:00 -0700, Kees Cook wrote:
> >>
> >> Oh! So it's gcc-version sensitive? That's alarming. Is this mapping correct:
> >>
> >> 4.8.5: WARN, eventual kernel hang
> >> 6.3.1, 7.0.1: WARN, but continues working
> >
> > Yeah, that's correct. I find that troubling, simply because this gcc
> > version has been through one hell of a lot of kernels with me. Yeah, I
> > know, that doesn't exempt it from having bugs, but color me suspicious.
>
> I still can't hit this with a 4.8.5 build. :(
>
> With _RATELIMIT removed, this should, in theory, report whatever goes
> negative first...

I applied the other patch you posted, and built with gcc-6.3.1 to
remove the gcc-4.8.5 aspect.  Look below the resulting splat.

[ 1.293962] NET: Registered protocol family 10
[ 1.294635] refcount_t silent saturation at in6_dev_get+0x25/0x104 in swapper/0[1], uid/euid: 0/0
[ 1.295616] ------------[ cut here ]------------
[ 1.296120] WARNING: CPU: 0 PID: 1 at kernel/panic.c:612 refcount_error_report+0x94/0x9e
[ 1.296950] Modules linked in:
[ 1.297276] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.13.0.g152d54a-tip-default #53
[ 1.299179] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
[ 1.300743] task: ffff88013ab84040 task.stack: ffffc9000062c000
[ 1.301825] RIP: 0010:refcount_error_report+0x94/0x9e
[ 1.302804] RSP: 0018:ffffc9000062fc10 EFLAGS: 00010282
[ 1.303791] RAX: 0000000000000055 RBX: ffffffff81a34274 RCX: ffffffff81c605e8
[ 1.304991] RDX: 0000000000000001 RSI: 0000000000000096 RDI: 0000000000000246
[ 1.306189] RBP: ffffc9000062fd58 R08: 0000000000000000 R09: 0000000000000175
[ 1.307392] R10: 0000000000000000 R11: 0000000000000001 R12: ffff88013ab84040
[ 1.308583] R13: 0000000000000000 R14: 0000000000000004 R15: ffffffff81a256c8
[ 1.309768] FS: 0000000000000000(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000
[ 1.311052] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1.312100] CR2: 00007f4631fe8df0 CR3: 0000000137d09003 CR4: 00000000001606f0
[ 1.313301] Call Trace:
[ 1.314012] ex_handler_refcount+0x63/0x70
[ 1.314893] fixup_exception+0x32/0x40
[ 1.315737] do_trap+0x8c/0x170
[ 1.316519] do_error_trap+0x70/0xd0
[ 1.317340] ? in6_dev_get+0x23/0x104
[ 1.318172] ? netlink_broadcast_filtered+0x2bd/0x430
[ 1.319156] ? kmem_cache_alloc_trace+0xce/0x5d0
[ 1.320098] ? set_debug_rodata+0x11/0x11
[ 1.320964] invalid_op+0x1e/0x30
[ 1.322520] RIP: 0010:in6_dev_get+0x25/0x104
[ 1.323631] RSP: 0018:ffffc9000062fe00 EFLAGS: 00010202
[ 1.324614] RAX: ffff880137de2400 RBX: ffff880137df4600 RCX: ffff880137de24f0
[ 1.325793] RDX: ffff88013a5e4000 RSI: 00000000fffffe00 RDI: ffff88013a5e4000
[ 1.326964] RBP: 00000000000000d1 R08: 0000000000000000 R09: ffff880137de7600
[ 1.328150] R10: 0000000000000000 R11: ffff8801398a4df8 R12: 0000000000000000
[ 1.329374] R13: ffffffff82137872 R14: 014200ca00000000 R15: 0000000000000000
[ 1.330547] ? set_debug_rodata+0x11/0x11
[ 1.331392] ip6_route_init_special_entries+0x2a/0x89
[ 1.332369] addrconf_init+0x9e/0x203
[ 1.333173] inet6_init+0x1af/0x365
[ 1.333956] ? af_unix_init+0x4e/0x4e
[ 1.334753] do_one_initcall+0x4e/0x190
[ 1.335555] ? set_debug_rodata+0x11/0x11
[ 1.336369] kernel_init_freeable+0x189/0x20e
[ 1.337230] ? rest_init+0xd0/0xd0
[ 1.337999] kernel_init+0xa/0xf7
[ 1.338744] ret_from_fork+0x25/0x30
[ 1.339500] Code: 48 8b 95 80 00 00 00 41 55 49 8d 8c 24 f0 0a 00 00 45 8b 84 24 10 09 00 00 41 89 c1 48 89 de 48 c7 c7 60 7a a3 81 e8 07 de 05 00 <0f> ff 58 5b 5d 41 5c 41 5d c3 0f 1f 44 00 00 55 48 89 e5 41 56
[ 1.342243] ---[ end trace b5d40c0fccce776c ]---

Back yours out, and...

# tracer: nop
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
swapper/0-1 [000] ...1 1.974114: in6_dev_getx: refs.counter:-1073741824
swapper/0-1 [000] ...1 1.974116: in6_dev_getx: refs.counter:-1073741824

---
arch/x86/include/asm/refcount.h | 9 +++++++++
include/net/addrconf.h | 12 ++++++++++++
net/ipv6/route.c | 4 ++--
3 files changed, 23 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/refcount.h
+++ b/arch/x86/include/asm/refcount.h
@@ -55,6 +55,15 @@ static __always_inline void refcount_inc
: : "cc", "cx");
}

+static __always_inline void refcount_inc_x(refcount_t *r)
+{
+ trace_printk("refs.counter:%d\n", r->refs.counter);
+ asm volatile(LOCK_PREFIX "incl %0\n\t"
+ REFCOUNT_CHECK_LT_ZERO
+ : [counter] "+m" (r->refs.counter)
+ : : "cc", "cx");
+}
+
static __always_inline void refcount_dec(refcount_t *r)
{
asm volatile(LOCK_PREFIX "decl %0\n\t"
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -321,6 +321,18 @@ static inline struct inet6_dev *in6_dev_
return idev;
}

+static inline struct inet6_dev *in6_dev_getx(const struct net_device *dev)
+{
+ struct inet6_dev *idev;
+
+ rcu_read_lock();
+ idev = rcu_dereference(dev->ip6_ptr);
+ if (idev)
+ refcount_inc_x(&idev->refcnt);
+ rcu_read_unlock();
+ return idev;
+}
+
static inline struct neigh_parms *__in6_dev_nd_parms_get_rcu(const struct net_device *dev)
{
struct inet6_dev *idev = __in6_dev_get(dev);
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -4044,9 +4044,9 @@ void __init ip6_route_init_special_entri
init_net.ipv6.ip6_null_entry->rt6i_idev = in6_dev_get(init_net.loopback_dev);
#ifdef CONFIG_IPV6_MULTIPLE_TABLES
init_net.ipv6.ip6_prohibit_entry->dst.dev = init_net.loopback_dev;
- init_net.ipv6.ip6_prohibit_entry->rt6i_idev = in6_dev_get(init_net.loopback_dev);
+ init_net.ipv6.ip6_prohibit_entry->rt6i_idev = in6_dev_getx(init_net.loopback_dev);
init_net.ipv6.ip6_blk_hole_entry->dst.dev = init_net.loopback_dev;
- init_net.ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_get(init_net.loopback_dev);
+ init_net.ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_getx(init_net.loopback_dev);
#endif
}

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