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Message-ID: <65ace546a7d55c2d6170ca88a48d3de402db2645.camel@linux.intel.com>
Date: Mon, 25 Nov 2024 11:06:38 +0100
From: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
To: Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com, will@...nel.org
Subject: Re: [PATCH AUTOSEL 6.12 3/5] locking/ww_mutex: Adjust to lockdep
nest_lock requirements
On Sun, 2024-11-24 at 07:46 -0500, Sasha Levin wrote:
> From: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
>
> [ Upstream commit 823a566221a5639f6c69424897218e5d6431a970 ]
>
> 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.
>
> This has the side effect that trying to lock a ww mutex *without* a
> ww_acquire_context but where a such context has been acquire, we'd
> see
> a lockdep splat. The test-ww_mutex.c selftest attempts to do that, so
> modify that particular test to not acquire a ww_acquire_context if it
> is not going to be used.
>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link:
> https://lkml.kernel.org/r/20241009092031.6356-1-thomas.hellstrom@linux.intel.com
> Signed-off-by: Sasha Levin <sashal@...nel.org>
It looks like the last version was not picked for this patch.
https://lore.kernel.org/all/172918113162.1279674.6570518059490493206@2413ebb6fbb6/T/
The version in this autosel patch regresses the locking api selftests
and should not be backported. Same for the corresponding backports for
6.11 and 6.6. Let me know if I should reply separately to those.
Thanks,
Thomas
> ---
> include/linux/ww_mutex.h | 14 ++++++++++++++
> kernel/locking/test-ww_mutex.c | 8 +++++---
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
> index bb763085479af..a401a2f31a775 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
> diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-
> ww_mutex.c
> index 10a5736a21c22..5d58b2c0ef98b 100644
> --- a/kernel/locking/test-ww_mutex.c
> +++ b/kernel/locking/test-ww_mutex.c
> @@ -62,7 +62,8 @@ static int __test_mutex(unsigned int flags)
> int ret;
>
> ww_mutex_init(&mtx.mutex, &ww_class);
> - ww_acquire_init(&ctx, &ww_class);
> + if (flags & TEST_MTX_CTX)
> + ww_acquire_init(&ctx, &ww_class);
>
> INIT_WORK_ONSTACK(&mtx.work, test_mutex_work);
> init_completion(&mtx.ready);
> @@ -90,7 +91,8 @@ static int __test_mutex(unsigned int flags)
> ret = wait_for_completion_timeout(&mtx.done,
> TIMEOUT);
> }
> ww_mutex_unlock(&mtx.mutex);
> - ww_acquire_fini(&ctx);
> + if (flags & TEST_MTX_CTX)
> + ww_acquire_fini(&ctx);
>
> if (ret) {
> pr_err("%s(flags=%x): mutual exclusion failure\n",
> @@ -679,7 +681,7 @@ static int __init test_ww_mutex_init(void)
> if (ret)
> return ret;
>
> - ret = stress(2047, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
> + ret = stress(2046, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
> if (ret)
> return ret;
>
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