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perf/core: Only copy-to-user after completely unlocking all locks, v3.
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We inadvertently create a dependency on mmap_sem with a whole chain.

This breaks any user who wants to take a lock and call rcu_barrier(),
while also taking that lock inside mmap_sem:

<4> [604.892532] ======================================================
<4> [604.892534] WARNING: possible circular locking dependency detected
<4> [604.892536] 5.6.0-rc7-CI-Patchwork_17096+ #1 Tainted: G     U
<4> [604.892537] ------------------------------------------------------
<4> [604.892538] kms_frontbuffer/2595 is trying to acquire lock:
<4> [604.892540] ffffffff8264a558 (rcu_state.barrier_mutex){+.+.}, at: rcu_barrier+0x23/0x190
<4> [604.892547]
but task is already holding lock:
<4> [604.892547] ffff888484716050 (reservation_ww_class_mutex){+.+.}, at: i915_gem_object_pin_to_display_plane+0x89/0x270 [i915]
<4> [604.892592]
which lock already depends on the new lock.
<4> [604.892593]
the existing dependency chain (in reverse order) is:
<4> [604.892594]
-> #6 (reservation_ww_class_mutex){+.+.}:
<4> [604.892597]        __ww_mutex_lock.constprop.15+0xc3/0x1090
<4> [604.892598]        ww_mutex_lock+0x39/0x70
<4> [604.892600]        dma_resv_lockdep+0x10e/0x1f5
<4> [604.892602]        do_one_initcall+0x58/0x300
<4> [604.892604]        kernel_init_freeable+0x17b/0x1dc
<4> [604.892605]        kernel_init+0x5/0x100
<4> [604.892606]        ret_from_fork+0x24/0x50
<4> [604.892607]
-> #5 (reservation_ww_class_acquire){+.+.}:
<4> [604.892609]        dma_resv_lockdep+0xec/0x1f5
<4> [604.892610]        do_one_initcall+0x58/0x300
<4> [604.892610]        kernel_init_freeable+0x17b/0x1dc
<4> [604.892611]        kernel_init+0x5/0x100
<4> [604.892612]        ret_from_fork+0x24/0x50
<4> [604.892613]
-> #4 (&mm->mmap_sem#2){++++}:
<4> [604.892615]        __might_fault+0x63/0x90
<4> [604.892617]        _copy_to_user+0x1e/0x80
<4> [604.892619]        perf_read+0x200/0x2b0
<4> [604.892621]        vfs_read+0x96/0x160
<4> [604.892622]        ksys_read+0x9f/0xe0
<4> [604.892623]        do_syscall_64+0x4f/0x220
<4> [604.892624]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [604.892625]
-> #3 (&cpuctx_mutex){+.+.}:
<4> [604.892626]        __mutex_lock+0x9a/0x9c0
<4> [604.892627]        perf_event_init_cpu+0xa4/0x140
<4> [604.892629]        perf_event_init+0x19d/0x1cd
<4> [604.892630]        start_kernel+0x362/0x4e4
<4> [604.892631]        secondary_startup_64+0xa4/0xb0
<4> [604.892631]
-> #2 (pmus_lock){+.+.}:
<4> [604.892633]        __mutex_lock+0x9a/0x9c0
<4> [604.892633]        perf_event_init_cpu+0x6b/0x140
<4> [604.892635]        cpuhp_invoke_callback+0x9b/0x9d0
<4> [604.892636]        _cpu_up+0xa2/0x140
<4> [604.892637]        do_cpu_up+0x61/0xa0
<4> [604.892639]        smp_init+0x57/0x96
<4> [604.892639]        kernel_init_freeable+0x87/0x1dc
<4> [604.892640]        kernel_init+0x5/0x100
<4> [604.892642]        ret_from_fork+0x24/0x50
<4> [604.892642]
-> #1 (cpu_hotplug_lock.rw_sem){++++}:
<4> [604.892643]        cpus_read_lock+0x34/0xd0
<4> [604.892644]        rcu_barrier+0xaa/0x190
<4> [604.892645]        kernel_init+0x21/0x100
<4> [604.892647]        ret_from_fork+0x24/0x50
<4> [604.892647]
-> #0 (rcu_state.barrier_mutex){+.+.}:
<4> [604.892649]        __lock_acquire+0x1328/0x15d0
<4> [604.892650]        lock_acquire+0xa7/0x1c0
<4> [604.892651]        __mutex_lock+0x9a/0x9c0
<4> [604.892652]        rcu_barrier+0x23/0x190
<4> [604.892680]        i915_gem_object_unbind+0x29d/0x3f0 [i915]
<4> [604.892707]        i915_gem_object_pin_to_display_plane+0x141/0x270 [i915]
<4> [604.892737]        intel_pin_and_fence_fb_obj+0xec/0x1f0 [i915]
<4> [604.892767]        intel_plane_pin_fb+0x3f/0xd0 [i915]
<4> [604.892797]        intel_prepare_plane_fb+0x13b/0x5c0 [i915]
<4> [604.892798]        drm_atomic_helper_prepare_planes+0x85/0x110
<4> [604.892827]        intel_atomic_commit+0xda/0x390 [i915]
<4> [604.892828]        drm_atomic_helper_set_config+0x57/0xa0
<4> [604.892830]        drm_mode_setcrtc+0x1c4/0x720
<4> [604.892830]        drm_ioctl_kernel+0xb0/0xf0
<4> [604.892831]        drm_ioctl+0x2e1/0x390
<4> [604.892833]        ksys_ioctl+0x7b/0x90
<4> [604.892835]        __x64_sys_ioctl+0x11/0x20
<4> [604.892835]        do_syscall_64+0x4f/0x220
<4> [604.892836]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [604.892837]

Changes since v1:
- Use (*values)[n++] in perf_read_one().
Changes since v2:
- Centrally allocate values.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200502171413.9133-1-chris@chris-wilson.co.uk
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
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@mlankhorst @rodrigovivi
mlankhorst authored and rodrigovivi committed Dec 28, 2022
1 parent ee5bc23 commit d972fd8
Showing 1 changed file with 25 additions and 24 deletions.
49 changes: 25 additions & 24 deletions kernel/events/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5500,20 +5500,16 @@ static int __perf_read_group_add(struct perf_event *leader,
}

static int perf_read_group(struct perf_event *event,
u64 read_format, char __user *buf)
u64 read_format, char __user *buf,
u64 *values)
{
struct perf_event *leader = event->group_leader, *child;
struct perf_event_context *ctx = leader->ctx;
int ret;
u64 *values;

lockdep_assert_held(&ctx->mutex);

values = kzalloc(event->read_size, GFP_KERNEL);
if (!values)
return -ENOMEM;

values[0] = 1 + leader->nr_siblings;
*values = 1 + leader->nr_siblings;

/*
* By locking the child_mutex of the leader we effectively
Expand All @@ -5531,25 +5527,17 @@ static int perf_read_group(struct perf_event *event,
goto unlock;
}

mutex_unlock(&leader->child_mutex);

ret = event->read_size;
if (copy_to_user(buf, values, event->read_size))
ret = -EFAULT;
goto out;

unlock:
mutex_unlock(&leader->child_mutex);
out:
kfree(values);
return ret;
}

static int perf_read_one(struct perf_event *event,
u64 read_format, char __user *buf)
u64 read_format, char __user *buf,
u64 *values)
{
u64 enabled, running;
u64 values[5];
int n = 0;

values[n++] = __perf_event_read_value(event, &enabled, &running);
Expand All @@ -5562,9 +5550,6 @@ static int perf_read_one(struct perf_event *event,
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&event->lost_samples);

if (copy_to_user(buf, values, n * sizeof(u64)))
return -EFAULT;

return n * sizeof(u64);
}

Expand All @@ -5585,7 +5570,8 @@ static bool is_event_hup(struct perf_event *event)
* Read the performance event - simple non blocking version for now
*/
static ssize_t
__perf_read(struct perf_event *event, char __user *buf, size_t count)
__perf_read(struct perf_event *event, char __user *buf,
size_t count, u64 *values)
{
u64 read_format = event->attr.read_format;
int ret;
Expand All @@ -5603,9 +5589,9 @@ __perf_read(struct perf_event *event, char __user *buf, size_t count)

WARN_ON_ONCE(event->ctx->parent_ctx);
if (read_format & PERF_FORMAT_GROUP)
ret = perf_read_group(event, read_format, buf);
ret = perf_read_group(event, read_format, buf, values);
else
ret = perf_read_one(event, read_format, buf);
ret = perf_read_one(event, read_format, buf, values);

return ret;
}
Expand All @@ -5615,16 +5601,31 @@ perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
struct perf_event *event = file->private_data;
struct perf_event_context *ctx;
u64 stack_values[8];
u64 *values;
int ret;

ret = security_perf_event_read(event);
if (ret)
return ret;

if (event->read_size <= sizeof(stack_values))
values = memset(stack_values, 0, event->read_size);
else
values = kzalloc(event->read_size, GFP_KERNEL);
if (!values)
return -ENOMEM;

ctx = perf_event_ctx_lock(event);
ret = __perf_read(event, buf, count);
ret = __perf_read(event, buf, count, values);
perf_event_ctx_unlock(event, ctx);

if (ret > 0 && copy_to_user(buf, values, ret))
ret = -EFAULT;

if (values != stack_values)
kfree(values);

return ret;
}

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