Quoting Tvrtko Ursulin (2020-04-29 14:42:44)
>
> On 28/04/2020 10:02, Chris Wilson wrote:
> > Once the intel_context is closed, the GEM context may be freed and so
> > the link from intel_context.gem_context is invalid.
> >
> > <3>[ 219.782944] BUG: KASAN: use-after-free in intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <3>[ 219.782996] Read of size 8 at addr ffff8881d7dff0b8 by task kworker/0:1/12
> >
> > <4>[ 219.783052] CPU: 0 PID: 12 Comm: kworker/0:1 Tainted: G U 5.7.0-rc2-g1f3ffd7683d54-kasan_118+ #1
> > <4>[ 219.783055] Hardware name: System manufacturer System Product Name/Z170 PRO GAMING, BIOS 3402 04/26/2017
> > <4>[ 219.783105] Workqueue: events heartbeat [i915]
> > <4>[ 219.783109] Call Trace:
> > <4>[ 219.783113] <IRQ>
> > <4>[ 219.783119] dump_stack+0x96/0xdb
> > <4>[ 219.783177] ? intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <4>[ 219.783182] print_address_description.constprop.6+0x16/0x310
> > <4>[ 219.783239] ? intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <4>[ 219.783295] ? intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <4>[ 219.783300] __kasan_report+0x137/0x190
> > <4>[ 219.783359] ? intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <4>[ 219.783366] kasan_report+0x32/0x50
> > <4>[ 219.783426] intel_engine_coredump_alloc+0x1bc3/0x2250 [i915]
> > <4>[ 219.783481] execlists_reset+0x39c/0x13d0 [i915]
> > <4>[ 219.783494] ? mark_held_locks+0x9e/0xe0
> > <4>[ 219.783546] ? execlists_hold+0xfc0/0xfc0 [i915]
> > <4>[ 219.783551] ? lockdep_hardirqs_on+0x348/0x5f0
> > <4>[ 219.783557] ? _raw_spin_unlock_irqrestore+0x34/0x60
> > <4>[ 219.783606] ? execlists_submission_tasklet+0x118/0x3a0 [i915]
> > <4>[ 219.783615] tasklet_action_common.isra.14+0x13b/0x410
> > <4>[ 219.783623] ? __do_softirq+0x1e4/0x9a7
> > <4>[ 219.783630] __do_softirq+0x226/0x9a7
> > <4>[ 219.783643] do_softirq_own_stack+0x2a/0x40
> > <4>[ 219.783647] </IRQ>
> > <4>[ 219.783692] ? heartbeat+0x3e2/0x10f0 [i915]
> > <4>[ 219.783696] do_softirq.part.13+0x49/0x50
> > <4>[ 219.783700] __local_bh_enable_ip+0x1a2/0x1e0
> > <4>[ 219.783748] heartbeat+0x409/0x10f0 [i915]
> > <4>[ 219.783801] ? __live_idle_pulse+0x9f0/0x9f0 [i915]
> > <4>[ 219.783806] ? lock_acquire+0x1ac/0x8a0
> > <4>[ 219.783811] ? process_one_work+0x811/0x1870
> > <4>[ 219.783827] ? rcu_read_lock_sched_held+0x9c/0xd0
> > <4>[ 219.783832] ? rcu_read_lock_bh_held+0xb0/0xb0
> > <4>[ 219.783836] ? _raw_spin_unlock_irq+0x1f/0x40
> > <4>[ 219.783845] process_one_work+0x8ca/0x1870
> > <4>[ 219.783848] ? lock_acquire+0x1ac/0x8a0
> > <4>[ 219.783852] ? worker_thread+0x1d0/0xb80
> > <4>[ 219.783864] ? pwq_dec_nr_in_flight+0x2c0/0x2c0
> > <4>[ 219.783870] ? do_raw_spin_lock+0x129/0x290
> > <4>[ 219.783886] worker_thread+0x82/0xb80
> > <4>[ 219.783895] ? __kthread_parkme+0xaf/0x1b0
> > <4>[ 219.783902] ? process_one_work+0x1870/0x1870
> > <4>[ 219.783906] kthread+0x34e/0x420
> > <4>[ 219.783911] ? kthread_create_on_node+0xc0/0xc0
> > <4>[ 219.783918] ret_from_fork+0x3a/0x50
> >
> > <3>[ 219.783950] Allocated by task 1264:
> > <4>[ 219.783975] save_stack+0x19/0x40
> > <4>[ 219.783978] __kasan_kmalloc.constprop.3+0xa0/0xd0
> > <4>[ 219.784029] i915_gem_create_context+0xa2/0xab8 [i915]
> > <4>[ 219.784081] i915_gem_context_create_ioctl+0x1fa/0x450 [i915]
> > <4>[ 219.784085] drm_ioctl_kernel+0x1d8/0x270
> > <4>[ 219.784088] drm_ioctl+0x676/0x930
> > <4>[ 219.784092] ksys_ioctl+0xb7/0xe0
> > <4>[ 219.784096] __x64_sys_ioctl+0x6a/0xb0
> > <4>[ 219.784100] do_syscall_64+0x94/0x530
> > <4>[ 219.784103] entry_SYSCALL_64_after_hwframe+0x49/0xb3
> >
> > <3>[ 219.784120] Freed by task 12:
> > <4>[ 219.784141] save_stack+0x19/0x40
> > <4>[ 219.784145] __kasan_slab_free+0x130/0x180
> > <4>[ 219.784148] kmem_cache_free_bulk+0x1bd/0x500
> > <4>[ 219.784152] kfree_rcu_work+0x1d8/0x890
> > <4>[ 219.784155] process_one_work+0x8ca/0x1870
> > <4>[ 219.784158] worker_thread+0x82/0xb80
> > <4>[ 219.784162] kthread+0x34e/0x420
> > <4>[ 219.784165] ret_from_fork+0x3a/0x50
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_gpu_error.c | 12 +++++++-----
> > 1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> > index 4d54dba35302..a976cd67b3b3 100644
> > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > @@ -1207,8 +1207,6 @@ static void engine_record_registers(struct intel_engine_coredump *ee)
> > static void record_request(const struct i915_request *request,
> > struct i915_request_coredump *erq)
> > {
> > - const struct i915_gem_context *ctx;
> > -
> > erq->flags = request->fence.flags;
> > erq->context = request->fence.context;
> > erq->seqno = request->fence.seqno;
> > @@ -1218,9 +1216,13 @@ static void record_request(const struct i915_request *request,
> >
> > erq->pid = 0;
> > rcu_read_lock();
> > - ctx = rcu_dereference(request->context->gem_context);
> > - if (ctx)
> > - erq->pid = pid_nr(ctx->pid);
> > + if (!intel_context_is_closed(request->context)) {
> > + const struct i915_gem_context *ctx;
> > +
> > + ctx = rcu_dereference(request->context->gem_context);
> > + if (ctx)
> > + erq->pid = pid_nr(ctx->pid);
> > + }
> > rcu_read_unlock();
> > }
> >
> >
>
> In the client busyness series I move the GEM ctx put to free_engines_rcu
> - at which point the closed check here is not needed any more. Should we
> delay this put right now to simplify? Maybe not.. I'll remember to tweak
> it in my series.
Yeah, it's not the right answer and I was hoping that you would have a
better plan :)
But it fixes a uaf we see atm, so a temporary bandaid.
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Regards,
>
> Tvrtko
>
> P.S. Fixes: 2e46a2a0b0149f951b63be1b5df6514676fed213 ?
Looks to be the culprit, yes.
-Chris
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