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Fri, 09 Oct 2026 03:18:52 -0700 (PDT) Received: from localhost.localdomain ([14.116.239.41]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4a2a858aa3esm1401367fac.12.2026.10.09.03.18.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2026 03:18:50 -0700 (PDT) From: Henry Martin To: Felix Kuehling , Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , David Airlie , Simona Vetter , Harry Wentland , Alex Hung Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Henry Martin Subject: [PATCH] amdkfd: fix doorbell allocation race creating duplicate allocations Date: Fri, 9 Oct 2026 18:18:42 +0800 Message-ID: <20261009101842.3294707-1-bsdhenrymartin@gmail.com> X-Mailer: git-send-email 2.43.7 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The check-and-allocate sequence on pdd->qpd.proc_doorbells is lockless at every call site of kfd_alloc_process_doorbells(): kfd_get_process_doorbells() (mmap of /dev/kfd), kfd_ioctl_create_queue() and the CRIU restore path each test the pointer under different locking (or none), so two racing threads can both observe NULL and each allocate a doorbell BO and bitmap, orphaning one allocation and handing the two mappings different backing pages. Move the serialization into kfd_alloc_process_doorbells() itself: take kfd->doorbell_mutex and re-check under it, so all three call sites are covered regardless of their own locking. The existing doorbell_mutex users (kfd_get_kernel_doorbell() / kfd_release_kernel_doorbell()) only guard the device-global kfd->doorbell_bitmap in short non-sleeping sections and never call into this path, so there is no nesting. This vulnerability was discovered by Tencent CodeBuddy Security. Fixes: 428542d91772 ("drm/amd/display: Setup for mmhubbub3_warmup_mcif with big buffer") Signed-off-by: Henry Martin --- drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c b/drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c index fdcf7f2d1b5b4..07f881573837e 100644 --- a/drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c +++ b/drivers/gpu/drm/amd/amdkfd/kfd_doorbell.c @@ -257,12 +257,21 @@ int kfd_alloc_process_doorbells(struct kfd_dev *kfd, struct kfd_process_device * int r; struct qcm_process_device *qpd = &pdd->qpd; + mutex_lock(&kfd->doorbell_mutex); + + /* Another thread may have won the check-and-allocate race */ + if (qpd->proc_doorbells) { + mutex_unlock(&kfd->doorbell_mutex); + return 0; + } + /* Allocate bitmap for dynamic doorbell allocation */ qpd->doorbell_bitmap = bitmap_zalloc(KFD_MAX_NUM_OF_QUEUES_PER_PROCESS, GFP_KERNEL); if (!qpd->doorbell_bitmap) { DRM_ERROR("Failed to allocate process doorbell bitmap\n"); - return -ENOMEM; + r = -ENOMEM; + goto unlock; } r = init_doorbell_bitmap(&pdd->qpd, kfd); @@ -284,11 +293,15 @@ int kfd_alloc_process_doorbells(struct kfd_dev *kfd, struct kfd_process_device * DRM_ERROR("Failed to allocate process doorbells\n"); goto err; } + + mutex_unlock(&kfd->doorbell_mutex); return 0; err: bitmap_free(qpd->doorbell_bitmap); qpd->doorbell_bitmap = NULL; +unlock: + mutex_unlock(&kfd->doorbell_mutex); return r; } -- 2.43.7