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Message-ID: <20230911084042.5160-1-thomas.hellstrom@linux.intel.com>
Date: Mon, 11 Sep 2023 10:40:42 +0200
From: Thomas Hellström
<thomas.hellstrom@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: Thomas Hellström
<thomas.hellstrom@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Daniel Vetter <daniel.vetter@...el.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Christian König <christian.koenig@....com>,
intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
dri-devel@...ts.freedestkop.org
Subject: [RFC PATCH] locking/ww_mutex: Adjust to lockdep nest_lock requirements
When using mutex_acquire_nest() with a nest_lock, lockdep refcounts the
number of acquired lockdep_maps of mutexes of the same class, and also
keeps a pointer to the first acquired lockdep_map of a class. That pointer
is then used for various comparison-, printing- and checking purposes,
but there is no mechanism to actively ensure that lockdep_map stays in
memory. Instead, a warning is printed if the lockdep_map is freed and
there are still held locks of the same lock class, even if the lockdep_map
itself has been released.
In the context of WW/WD transactions that means that if a user unlocks
and frees a ww_mutex from within an ongoing ww transaction, and that
mutex happens to be the first ww_mutex grabbed in the transaction,
such a warning is printed and there might be a risk of a UAF.
Note that this is only problem when lockdep is enabled and affects only
dereferences of struct lockdep_map.
Adjust to this by adding a fake lockdep_map to the acquired context and
make sure it is the first acquired lockdep map of the associated
ww_mutex class. Then hold it for the duration of the WW/WD transaction.
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Daniel Vetter <daniel.vetter@...el.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: Christian König <christian.koenig@....com>
Cc: intel-xe@...ts.freedesktop.org
Cc: intel-gfx@...ts.freedesktop.org
Cc: dri-devel@...ts.freedestkop.org
Signed-off-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
---
include/linux/ww_mutex.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index bb763085479a..a401a2f31a77 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -65,6 +65,16 @@ struct ww_acquire_ctx {
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
+ /**
+ * @first_lock_dep_map: fake lockdep_map for first locked ww_mutex.
+ *
+ * lockdep requires the lockdep_map for the first locked ww_mutex
+ * in a ww transaction to remain in memory until all ww_mutexes of
+ * the transaction have been unlocked. Ensure this by keeping a
+ * fake locked ww_mutex lockdep map between ww_acquire_init() and
+ * ww_acquire_fini().
+ */
+ struct lockdep_map first_lock_dep_map;
#endif
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
unsigned int deadlock_inject_interval;
@@ -146,7 +156,10 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
&ww_class->acquire_key, 0);
+ lockdep_init_map(&ctx->first_lock_dep_map, ww_class->mutex_name,
+ &ww_class->mutex_key, 0);
mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
+ mutex_acquire_nest(&ctx->first_lock_dep_map, 0, 0, &ctx->dep_map, _RET_IP_);
#endif
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
ctx->deadlock_inject_interval = 1;
@@ -185,6 +198,7 @@ static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ mutex_release(&ctx->first_lock_dep_map, _THIS_IP_);
mutex_release(&ctx->dep_map, _THIS_IP_);
#endif
#ifdef DEBUG_WW_MUTEXES
--
2.41.0
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