Commit a8c15954 authored Sep 03, 2019 by Chris Wilson

drm/i915: Protect debugfs per_file_stats with RCU lock



If we make sure we grab a strong reference to each object as we dump it,
we can reduce the locks outside of our iterators to an rcu_read_lock.

This should prevent errors like:
[ 2138.371911] BUG: KASAN: use-after-free in per_file_stats+0x43/0x380 [i915]
[ 2138.371924] Read of size 8 at addr ffff888223651000 by task cat/8293

[ 2138.371947] CPU: 0 PID: 8293 Comm: cat Not tainted 5.3.0-rc6-CI-Custom_4352+ #1
[ 2138.371953] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./J4205-ITX, BIOS P1.40 07/14/2017
[ 2138.371959] Call Trace:
[ 2138.371974]  dump_stack+0x7c/0xbb
[ 2138.372099]  ? per_file_stats+0x43/0x380 [i915]
[ 2138.372108]  print_address_description+0x73/0x3a0
[ 2138.372231]  ? per_file_stats+0x43/0x380 [i915]
[ 2138.372352]  ? per_file_stats+0x43/0x380 [i915]
[ 2138.372362]  __kasan_report+0x14e/0x192
[ 2138.372489]  ? per_file_stats+0x43/0x380 [i915]
[ 2138.372502]  kasan_report+0xe/0x20
[ 2138.372625]  per_file_stats+0x43/0x380 [i915]
[ 2138.372751]  ? i915_panel_show+0x110/0x110 [i915]
[ 2138.372761]  idr_for_each+0xa7/0x160
[ 2138.372773]  ? idr_get_next_ul+0x110/0x110
[ 2138.372782]  ? do_raw_spin_lock+0x10a/0x1d0
[ 2138.372923]  print_context_stats+0x264/0x510 [i915]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: David Weinehall <david.weinehall@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190903062133.27360-1-chris@chris-wilson.co.uk

parent aaef8510

drivers/gpu/drm/i915/i915_debugfs.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -237,6 +237,9 @@ static int per_file_stats(int id, void ptr, void data)
		struct file_stats *stats = data;
		struct i915_vma *vma;

		if (!kref_get_unless_zero(&obj->base.refcount))
		return 0;

		stats->count++;
		stats->total += obj->base.size;
		if (!atomic_read(&obj->bind_count))
		@@ -284,6 +287,7 @@ static int per_file_stats(int id, void ptr, void data)
		}
		spin_unlock(&obj->vma.lock);

		i915_gem_object_put(obj);
		return 0;
		}

		@@ -313,10 +317,12 @@ static void print_context_stats(struct seq_file *m,
		i915_gem_context_lock_engines(ctx), it) {
		intel_context_lock_pinned(ce);
		if (intel_context_is_pinned(ce)) {
		rcu_read_lock();
		if (ce->state)
		per_file_stats(0,
		ce->state->obj, &kstats);
		per_file_stats(0, ce->ring->vma->obj, &kstats);
		rcu_read_unlock();
		}
		intel_context_unlock_pinned(ce);
		}
		@@ -328,9 +334,9 @@ static void print_context_stats(struct seq_file *m,
		struct task_struct *task;
		char name[80];

		spin_lock(&file->table_lock);
		rcu_read_lock();
		idr_for_each(&file->object_idr, per_file_stats, &stats);
		spin_unlock(&file->table_lock);
		rcu_read_unlock();

		rcu_read_lock();
		task = pid_task(ctx->pid ?: file->pid, PIDTYPE_PID);

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