From nobody Sun Nov 24 16:57:18 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C2B9F1B394E; Mon, 4 Nov 2024 11:19:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730719189; cv=none; b=LTw8FF0c6eDB340xjygTPtnOSaVDgkBxa3ocEXaYx3wrhtCvg9aew7pwxqDnH0ipvz6SGkrXF+YhkWLoXvbr3JEx1znXrGmrt3eJOYN8+egtchk18OWWOQigM1/C+nJII8Zou6on23495nEMvIN/OOwMgMO3eLq+RAWk9KPSBIw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730719189; c=relaxed/simple; bh=w4DhfcqhD35OLZhCD/yjFqQsPzQFGG5lrGkMuG3Ix1U=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=DlaWkAshJNQPZc0+aAHJ18kzzp649qN62+ki7aWWWUOimlhHAXwkSfMEMfQjszkuaSQLpeeYn/XeypJ524hyYvPNH+Ugfm7T2CgNhbbISCUTvJehjINCg66h6yvJ9Pz7taWDFjYaIJpV7FOeTbGODacvo8K4y+eOOLqzhaWbocg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 966C9C4CECE; Mon, 4 Nov 2024 11:19:47 +0000 (UTC) From: Catalin Marinas To: iommu@lists.linux.dev, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Ido Schimmel , Ido Schimmel , Robin Murphy , Joerg Roedel , Will Deacon , Andrew Morton Subject: [PATCH] kmemleak: iommu/iova: Fix transient kmemleak false positive Date: Mon, 4 Nov 2024 11:19:44 +0000 Message-Id: <20241104111944.2207155-1-catalin.marinas@arm.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The introduction of iova_depot_pop() in 911aa1245da8 ("iommu/iova: Make the rcache depot scale better") confused kmemleak by moving a struct iova_magazine object from a singly linked list to rcache->depot and resetting the 'next' pointer referencing it. Unlike doubly linked lists, the content of the object being referred is never changed on removal from a singly linked list and the kmemleak checksum heuristics do not detect such scenario. This leads to false positives like: unreferenced object 0xffff8881a5301000 (size 1024): comm "softirq", pid 0, jiffies 4306297099 (age 462.991s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 e7 7d 05 00 00 00 00 00 .........}...... 0f b4 05 00 00 00 00 00 b4 96 05 00 00 00 00 00 ................ backtrace: [] __kmem_cache_alloc_node+0x1e8/0x320 [] kmalloc_trace+0x2a/0x60 [] free_iova_fast+0x28e/0x4e0 [] fq_ring_free_locked+0x1b0/0x310 [] fq_flush_timeout+0x19d/0x2e0 [] call_timer_fn+0x19a/0x5c0 [] __run_timers+0x78b/0xb80 [] run_timer_softirq+0x5d/0xd0 [] __do_softirq+0x205/0x8b5 Introduce kmemleak_transient_leak() which resets the object checksum requiring another scan pass before it is reported (if still unreferenced). Call this new API in iova_depot_pop(). Signed-off-by: Catalin Marinas Reported-by: Ido Schimmel Tested-by: Ido Schimmel Cc: Robin Murphy Cc: Joerg Roedel Cc: Will Deacon Cc: Andrew Morton Link: https://lore.kernel.org/r/ZY1osaGLyT-sdKE8@shredder/ Acked-by: Robin Murphy --- This could be two patches but I thought the rationale for a new kmemleak API goes better with its use in the iova code. Happy to move the 6 lines iova change to a separate patch but they should still go in together. Given that there are more line under mm/, I'd say it better goes in via the mm tree with the relevant acks from the iommu folk. Thanks. Documentation/dev-tools/kmemleak.rst | 1 + drivers/iommu/iova.c | 6 +++++ include/linux/kmemleak.h | 4 +++ mm/kmemleak.c | 39 ++++++++++++++++++++++++++++ 4 files changed, 50 insertions(+) diff --git a/Documentation/dev-tools/kmemleak.rst b/Documentation/dev-tools= /kmemleak.rst index 2cb00b53339f..7d784e03f3f9 100644 --- a/Documentation/dev-tools/kmemleak.rst +++ b/Documentation/dev-tools/kmemleak.rst @@ -161,6 +161,7 @@ See the include/linux/kmemleak.h header for the functio= ns prototype. - ``kmemleak_free_percpu`` - notify of a percpu memory block freeing - ``kmemleak_update_trace`` - update object allocation stack trace - ``kmemleak_not_leak`` - mark an object as not a leak +- ``kmemleak_transient_leak`` - mark an object as a transient leak - ``kmemleak_ignore`` - do not scan or report an object as leak - ``kmemleak_scan_area`` - add scan areas inside a memory block - ``kmemleak_no_scan`` - do not scan a memory block diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 16c6adff3eb7..5b5400efb657 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -6,6 +6,7 @@ */ =20 #include +#include #include #include #include @@ -673,6 +674,11 @@ static struct iova_magazine *iova_depot_pop(struct iov= a_rcache *rcache) { struct iova_magazine *mag =3D rcache->depot; =20 + /* + * As the mag->next pointer is moved to rcache->depot and reset via + * the mag->size assignment, mark it as a transient false positive. + */ + kmemleak_transient_leak(mag->next); rcache->depot =3D mag->next; mag->size =3D IOVA_MAG_SIZE; rcache->depot_size--; diff --git a/include/linux/kmemleak.h b/include/linux/kmemleak.h index 6a3cd1bf4680..93a73c076d16 100644 --- a/include/linux/kmemleak.h +++ b/include/linux/kmemleak.h @@ -26,6 +26,7 @@ extern void kmemleak_free_part(const void *ptr, size_t si= ze) __ref; extern void kmemleak_free_percpu(const void __percpu *ptr) __ref; extern void kmemleak_update_trace(const void *ptr) __ref; extern void kmemleak_not_leak(const void *ptr) __ref; +extern void kmemleak_transient_leak(const void *ptr) __ref; extern void kmemleak_ignore(const void *ptr) __ref; extern void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) __= ref; extern void kmemleak_no_scan(const void *ptr) __ref; @@ -93,6 +94,9 @@ static inline void kmemleak_update_trace(const void *ptr) static inline void kmemleak_not_leak(const void *ptr) { } +static inline void kmemleak_transient_leak(const void *ptr) +{ +} static inline void kmemleak_ignore(const void *ptr) { } diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 0400f5e8ac60..72e09ac9140b 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -934,6 +934,28 @@ static void make_black_object(unsigned long ptr, unsig= ned int objflags) paint_ptr(ptr, KMEMLEAK_BLACK, objflags); } =20 +/* + * Reset the checksum of an object. The immediate effect is that it will n= ot + * be reported as a leak during the next scan until its checksum is update= d. + */ +static void reset_checksum(unsigned long ptr) +{ + unsigned long flags; + struct kmemleak_object *object; + + object =3D find_and_get_object(ptr, 0); + if (!object) { + kmemleak_warn("Not resetting the checksum of an unknown object at 0x%08l= x\n", + ptr); + return; + } + + raw_spin_lock_irqsave(&object->lock, flags); + object->checksum =3D 0; + raw_spin_unlock_irqrestore(&object->lock, flags); + put_object(object); +} + /* * Add a scanning area to the object. If at least one such area is added, * kmemleak will only scan these ranges rather than the whole memory block. @@ -1202,6 +1224,23 @@ void __ref kmemleak_not_leak(const void *ptr) } EXPORT_SYMBOL(kmemleak_not_leak); =20 +/** + * kmemleak_transient_leak - mark an allocated object as transient false p= ositive + * @ptr: pointer to beginning of the object + * + * Calling this function on an object will cause the memory block to not be + * reported as a leak temporarily. This may happen, for example, if the ob= ject + * is part of a singly linked list and the ->next reference to it is chang= ed. + */ +void __ref kmemleak_transient_leak(const void *ptr) +{ + pr_debug("%s(0x%px)\n", __func__, ptr); + + if (kmemleak_enabled && ptr && !IS_ERR(ptr)) + reset_checksum((unsigned long)ptr); +} +EXPORT_SYMBOL(kmemleak_transient_leak); + /** * kmemleak_ignore - ignore an allocated object * @ptr: pointer to beginning of the object