Re: [PATCH v3 0/2] driver core: add TAINT_FORCED_BIND for when userspace manually messes with devices and drivers
From: Armin Wolf <W_Armin@gmx.de>
Date: 2026-09-04 19:47:36
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driver-core, linux-doc, linux-modules, linux-usb, lkml
Am 04.09.26 um 07:10 schrieb Greg Kroah-Hartman:
The ability to add and remove devices from a driver through the sysfs "bind" and "unbind" files was created all those decades ago as a way that kernel developers can iterate faster, and provide a debugging way for users to attempt to add a new device to a driver without having to rebuild their kernel. This api over the years has been abused and recently come under a major fuzzing "attack" through tools like syzbot which decided that it would attempt to just randomly bind any driver to any type of device, causing loads of unneeded errors and pointless kernel patches to be generated by unsuspecting new developers. Handle all of this by adding a new taint flag, TAINT_FORCED_BIND, which will be set on the driver if the bind/unbind sysfs files are ever written to. This lets kernel developers "know" that a user is attempting to do something that is not normal, and as such, if the kernel breaks they get to keep the shiny pieces laying around on the floor. The flag is 'Y' which was unused, and can remembered as the user is "yeeting" the device being operated on here (thrown with force without regard for the thing being thrown). Note, the taint flag gets set _BEFORE_ the bind/unbind callback happens, as many times crashes/oops/warnings/failures happen within the callback, and the taint flag needs to be there to show what was being attempted. If it were to be set after the callback happens, the oops report would not properly reflect what foolishness was being attempted. Fuzzing tools like syzbot, that doesn't have hand-crafted rules to keep the tool from hitting bind/unbind, should be run with panic_on_taint enabled so that they fall over and don't continue on, thinking that they actually found a real issue. Userspace operations that rely on the bind/unbind files to work around the lack of will to upgrade a kernel image to a newer version with proper support for new devices, or the lack of will to submit valid device ids to driver authors, will still work properly, but now the kernel will be flagged in a way that will show that perhaps those users should reconsider their behavior and work to have the drivers properly support these devices in a "native" manner.
What about users that use driver_override together with vfio-pci? AFAIK they still need to write to bind/unbind. Also i always liked the fact that the bind/unbind attributes make it very easy in creating generic drivers. In fact, i am intending to use this feature in order to add netlink support to the ACPI-WMI subsystem in the future. I am planning to realize this thru a generic WMI driver that has to be manually bound to a given WMI device to make it available over netlink, so having users be able to write bind/unbind without potentially triggering a kernel panic would be very nice. Additionally, writing into the bind attribute still checks if the driver and the device match: /* * Manually attach a device to a driver. * Note: the driver must want to bind to the device, * it is not possible to override the driver's id table. */ static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t count) Because of this i would suggest that the taint (if at all) be added to the driver_override attribute instead, because only with this attribute users can bind random drivers to truly random devices. Thanks, Armin Wolf
quoted hunk ↗ jump to hunk
Finally, the bind/unbind files can find real use-after-free issues with some drivers by forcing the process to happen virtually without having to rely on manual removal processes. Those real bugs should still be worked on, but by adding this taint flag, developers can more easily determine bug reports that are actually worth looking at. Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- Changes in v3: - Fixes based on sashiko review: - Fix up prototype for when CONFIG_MODULES is disabled so it will build properly, AGAIN. - Link to v2: https://patch.msgid.link/20260831-bind_taint-v2-0-1082d631213b@linuxfoundation.org Changes in v2: - rebase on 7.3-rc1 - Add changelog text to describe panic_on_taint and how it should be set for tools like syzbot. - Add changelog text to describe why 'Y' was picked. - Fixes based on sashiko review: - Make add_taint_module() handle a NULL for module pointer, fixing a problem with built-in drivers. - Fix up prototype for when CONFIG_MODULES is disabled so it will actually build properly. - rst table header fixes. - Link to v1: https://patch.msgid.link/20260826-bind_taint-v1-0-52b05f4a965c@linuxfoundation.org To: Luis Chamberlain <mcgrof@kernel.org> To: Petr Pavlu <petr.pavlu@suse.com> To: Daniel Gomez <da.gomez@kernel.org> To: Sami Tolvanen <samitolvanen@google.com> To: Aaron Tomlin <atomlin@atomlin.com> To: Jonathan Corbet <corbet@lwn.net> To: Shuah Khan <skhan@linuxfoundation.org> To: Randy Dunlap <rdunlap@infradead.org> To: Greg Kroah-Hartman <gregkh@linuxfoundation.org> To: "Rafael J. Wysocki" <rafael@kernel.org> To: Danilo Krummrich <dakr@kernel.org> To: Steven Rostedt <rostedt@goodmis.org> To: Masami Hiramatsu <mhiramat@kernel.org> To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: linux-modules@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: driver-core@lists.linux.dev Cc: linux-trace-kernel@vger.kernel.org --- Greg Kroah-Hartman (2): module: pull out add_taint_module() to be public driver core: add TAINT_FORCED_BIND for when userspace manually messes with devices and drivers Documentation/admin-guide/tainted-kernels.rst | 52 ++++++++++++++------------- drivers/base/bus.c | 3 ++ include/linux/module.h | 10 ++++++ include/linux/panic.h | 3 +- include/trace/events/module.h | 3 +- kernel/module/main.c | 16 +++++++-- kernel/panic.c | 5 +-- tools/debugging/kernel-chktaint | 8 +++++ 8 files changed, 69 insertions(+), 31 deletions(-) --- base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 change-id: 20260825-bind_taint-d4077b870bc4 Best regards, -- Greg Kroah-Hartman [off-list ref] From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 BCB7D415F06; Fri, 4 Sep 2026 05:12:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788498755; cv=none; b=YVFqay1IJUVOWRhF5lbF49N9gACjWl/u/wiBGdeV8d9eqXk9mnp+dQ6eyjskPf1vqMRfNXCLudsRqs7s/ptpX2bQJsQ4PyAt97qclTSJBOznKuYqjuVxufSShWBSj6iGoGnZcQw+e2Q9Ly6ixw+Q323AmyXIc+H/caHtjxakuHk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788498755; c=relaxed/simple; bh=pLyyPJCavNnqg1J4ue9yK5PlAmiMR++3Z8v4Ev3jR+4=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=NoNrP4+kG51E+VUVjTQ7eZBG8DJ4QJdPSX7nXCHR7qNw1HzTheBF+APlqE/yPFE/HDXCloQq6PsRH784NlK0lTDBu81Xo9PlS0QhLQkafpUGps8FcEw2pQZxbhT+91ISzyOG0uOnSka9ty7gwBGsyKlxA8KNYgFLv4Jpuyl3CxU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ucn4lrR/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ucn4lrR/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 003711F00A3E; Fri, 4 Sep 2026 05:12:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788498754; bh=KrAwo9/bReRcHGrb+EIOBXbKoLVbmnWAiqQj4hM9GR4=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=ucn4lrR/Wvs8Hzz+jBIP38JWRP4T8gs3TOfl/opgMz+qXDSpJTTmTld3GSYkHx+b1 pqksgdzktExbEkSrSC3Poy+I6JfuzXpXH199wNaRrrq4ei16vWNsuDsnGyxgiHzh0C nbHTwZKC7lvKjyIz2vK00XrqIQLoA4eUS5NrG24U= From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Date: Fri, 04 Sep 2026 07:10:41 +0200 Subject: [PATCH v3 1/2] module: pull out add_taint_module() to be public Precedence: bulk X-Mailing-List: linux-modules@vger.kernel.org List-Id: <linux-modules.vger.kernel.org> List-Subscribe: <mailto:linux-modules+subscribe@vger.kernel.org> List-Unsubscribe: <mailto:linux-modules+unsubscribe@vger.kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: [ref] References: [ref] In-Reply-To: [ref] To: Luis Chamberlain <mcgrof@kernel.org>, Petr Pavlu <petr.pavlu@suse.com>, Daniel Gomez [off-list ref], Sami Tolvanen [off-list ref], Aaron Tomlin [off-list ref], Jonathan Corbet [off-list ref], Shuah Khan [off-list ref], Randy Dunlap [off-list ref], "Rafael J. Wysocki" [off-list ref], Danilo Krummrich [off-list ref], Steven Rostedt [off-list ref], Masami Hiramatsu [off-list ref], Mathieu Desnoyers [off-list ref] Cc: Bradley Morgan <redacted>, Aleksandr Nogikh [off-list ref], linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, driver-core@lists.linux.dev, linux-trace-kernel@vger.kernel.org, Greg Kroah-Hartman [off-list ref], Johan Hovold [off-list ref] X-Mailer: b4 0.17-dev-362b8 X-Developer-Signature: v=1; a=openpgp-sha256; l=2682; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=pLyyPJCavNnqg1J4ue9yK5PlAmiMR++3Z8v4Ev3jR+4=; b=owGbwMvMwCRo6H6F97bub03G02pJDFmzgq4fWPbWcV/uvHnfg/ZMrU9bv71xatg7tVk7novmL 1mmFli4riOWhUGQiUFWTJHlyzaeo/srDil6GdqehpnDygQyhIGLUwAmosTDMIdTKWjC6aIHLY+P emcEXORcfPbdG0mGuULdv/erqSxsnFs4z/HElrKuTU5rdAE= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Other kernel code might want to call add_taint_module() so pull it out and make it global. If modules are not enabled, this defaults to a call to add_taint(), so all is fine. Reviewed-by: Johan Hovold <johan@kernel.org> Tested-by: Johan Hovold <johan@kernel.org> Reviewed-by: Bradley Morgan <redacted> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- include/linux/module.h | 10 ++++++++++ kernel/module/main.c | 16 +++++++++++++--- 2 files changed, 23 insertions(+), 3 deletions(-)diff --git a/include/linux/module.h b/include/linux/module.h index 96cc98568eea..f6f90cd88f15 100644 --- a/include/linux/module.h +++ b/include/linux/module.h@@ -29,6 +29,7 @@ #include <linux/srcu.h> #include <linux/static_call_types.h> #include <linux/dynamic_debug.h> +#include <linux/panic.h> #include <linux/percpu.h> #include <asm/module.h>@@ -770,6 +771,9 @@ static inline bool is_livepatch_module(struct module *mod) void module_for_each_mod(int(*func)(struct module *mod, void *data), void *data); +void add_taint_module(struct module *mod, unsigned flag, + enum lockdep_ok lockdep_ok); + #else /* !CONFIG_MODULES... */ static inline struct module *__module_address(unsigned long addr)@@ -877,6 +881,12 @@ static inline bool module_is_coming(struct module *mod) static inline void module_for_each_mod(int(*func)(struct module *mod, void *data), void *data) { } + +static inline void add_taint_module(struct module *mod, unsigned flag, + enum lockdep_ok lockdep_ok) +{ + add_taint(flag, lockdep_ok); +} #endif /* CONFIG_MODULES */ #ifdef CONFIG_SYSFSdiff --git a/kernel/module/main.c b/kernel/module/main.c index d0e1e0bd2ad0..444d990c9983 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c@@ -191,11 +191,21 @@ static inline int strong_try_module_get(struct module *mod) return -ENOENT; } -static inline void add_taint_module(struct module *mod, unsigned flag, - enum lockdep_ok lockdep_ok) +/** + * add_taint_module: add a taint flag if not already set for a specific module + * @mod: pointer to the module that caused the problem + * @flag: one of the TAINT_* constants. + * @lockdep_ok: whether lock debugging is still OK. + * + * If something bad has gone wrong, you'll want @lockdebug_ok = false, but for + * some noteworthy-but-not-corrupting cases, it can be set to true. + */ +void add_taint_module(struct module *mod, unsigned flag, + enum lockdep_ok lockdep_ok) { add_taint(flag, lockdep_ok); - set_bit(flag, &mod->taints); + if (mod) + set_bit(flag, &mod->taints); } /*