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([2601:188:c100:5710:627d:9ff:fe85:9ade]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-471c2b06532sm18535991cf.79.2025.02.14.07.30.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2025 07:30:20 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <12563ec0-90ef-4613-9931-319b2a2bfceb@redhat.com> Date: Fri, 14 Feb 2025 10:30:18 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/4] locking/lockdep: Add kasan_check_byte() check in lock_acquire() To: Marco Elver , Waiman Long Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com References: <20250213200228.1993588-1-longman@redhat.com> <20250213200228.1993588-5-longman@redhat.com> <3d069c26-4971-415a-9751-a28d207feb43@redhat.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/14/25 9:44 AM, Marco Elver wrote: > On Fri, 14 Feb 2025 at 15:09, Waiman Long wrote: >> On 2/14/25 5:44 AM, Marco Elver wrote: >>> On Thu, 13 Feb 2025 at 21:02, Waiman Long wrote: >>>> KASAN instrumentation of lockdep has been disabled as we don't need >>>> KASAN to check the validity of lockdep internal data structures and >>>> incur unnecessary performance overhead. However, the lockdep_map pointer >>>> passed in externally may not be valid (e.g. use-after-free) and we run >>>> the risk of using garbage data resulting in false lockdep reports. Add >>>> kasan_check_byte() call in lock_acquire() for non kernel core data >>>> object to catch invalid lockdep_map and abort lockdep processing if >>>> input data isn't valid. >>>> >>>> Suggested-by: Marco Elver >>>> Signed-off-by: Waiman Long >>> Reviewed-by: Marco Elver >>> >>> but double-check if the below can be simplified. >>> >>>> --- >>>> kernel/locking/lock_events_list.h | 1 + >>>> kernel/locking/lockdep.c | 14 ++++++++++++++ >>>> 2 files changed, 15 insertions(+) >>>> >>>> diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h >>>> index 9ef9850aeebe..bed59b2195c7 100644 >>>> --- a/kernel/locking/lock_events_list.h >>>> +++ b/kernel/locking/lock_events_list.h >>>> @@ -95,3 +95,4 @@ LOCK_EVENT(rtmutex_deadlock) /* # of rt_mutex_handle_deadlock()'s */ >>>> LOCK_EVENT(lockdep_acquire) >>>> LOCK_EVENT(lockdep_lock) >>>> LOCK_EVENT(lockdep_nocheck) >>>> +LOCK_EVENT(lockdep_kasan_fail) >>>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c >>>> index 8436f017c74d..98dd0455d4be 100644 >>>> --- a/kernel/locking/lockdep.c >>>> +++ b/kernel/locking/lockdep.c >>>> @@ -57,6 +57,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include >>>> >>>> @@ -5830,6 +5831,19 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass, >>>> if (!debug_locks) >>>> return; >>>> >>>> + /* >>>> + * As KASAN instrumentation is disabled and lock_acquire() is usually >>>> + * the first lockdep call when a task tries to acquire a lock, add >>>> + * kasan_check_byte() here to check for use-after-free of non kernel >>>> + * core lockdep_map data to avoid referencing garbage data. >>>> + */ >>>> + if (unlikely(IS_ENABLED(CONFIG_KASAN) && >>> This is not needed - kasan_check_byte() will always return true if >>> KASAN is disabled or not compiled in. >> I added this check because of the is_kernel_core_data() call. >>>> + !is_kernel_core_data((unsigned long)lock) && >>> Why use !is_kernel_core_data()? Is it to improve performance? >> Not exactly. In my testing, just using kasan_check_byte() doesn't quite >> work out. It seems to return false positive in some cases causing >> lockdep splat. I didn't look into exactly why this happens and I added >> the is_kernel_core_data() call to work around that. > Globals should have their shadow memory unpoisoned by default, so > that's definitely odd. > > Out of curiosity, do you have such a false positive splat? Wondering > which data it's accessing. Maybe that'll tell us more about what's > wrong. Will do more investigation about this and let you know the result. Cheers, Longman >