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[91.14.161.181]) by smtp.gmail.com with ESMTPSA id y4sm4646352wmi.22.2021.08.18.03.54.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 03:54:46 -0700 (PDT) From: " =?utf-8?q?Christian_K=C3=B6nig?= " X-Google-Original-From: =?utf-8?q?Christian_K=C3=B6nig?= To: hridya@google.com, john.stultz@linaro.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, gustavo@padovan.org, linux-media@vger.kernel.org, adelva@google.com, sspatil@google.com, daniel@ffwll.ch Subject: [PATCH 2/2] dma-buf: taint the kernel on sw_sync use Date: Wed, 18 Aug 2021 12:54:43 +0200 Message-Id: <20210818105443.1578-2-christian.koenig@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210818105443.1578-1-christian.koenig@amd.com> References: <20210818105443.1578-1-christian.koenig@amd.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org As we now knew allowing userspace control over dma_fence synchronization is fundamentally broken and can cause deadlocks inside the kernel memory management. Because of this harden the wording for CONFIG_SW_SYNC and taint the kernel as soon as it is used. Signed-off-by: Christian König --- drivers/dma-buf/Kconfig | 5 +++-- drivers/dma-buf/sw_sync.c | 5 ++++- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 9561e3d2d428..61e0f3c5ba8b 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -27,8 +27,9 @@ config SW_SYNC synchronization. Useful when there is no hardware primitive backing the synchronization. - WARNING: improper use of this can result in deadlocking kernel - drivers from userspace. Intended for test and debug only. + WARNING: improper use of this can result in deadlocking the kernel + memory management from userspace. Intended for test and debug only. + Use at your own risk. config UDMABUF bool "userspace dmabuf misc driver" diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index 348b3a9170fa..c2bcb9062f51 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -286,7 +286,8 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj, /* * *WARNING* * - * improper use of this can result in deadlocking kernel drivers from userspace. + * improper use of this can result in deadlocking kernel memory management + * from userspace. */ /* opening sw_sync create a new sync obj */ @@ -295,6 +296,8 @@ static int sw_sync_debugfs_open(struct inode *inode, struct file *file) struct sync_timeline *obj; char task_comm[TASK_COMM_LEN]; + add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); + get_task_comm(task_comm, current); obj = sync_timeline_create(task_comm);