From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- Documentation/usb/authorization.rst | 129 ++++++++++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+) create mode 100644 Documentation/usb/authorization.rst (limited to 'Documentation/usb/authorization.rst') diff --git a/Documentation/usb/authorization.rst b/Documentation/usb/authorization.rst new file mode 100644 index 000000000..150a14970 --- /dev/null +++ b/Documentation/usb/authorization.rst @@ -0,0 +1,129 @@ +============================================================== +Authorizing (or not) your USB devices to connect to the system +============================================================== + +Copyright (C) 2007 Inaky Perez-Gonzalez Intel Corporation + +This feature allows you to control if a USB device can be used (or +not) in a system. This feature will allow you to implement a lock-down +of USB devices, fully controlled by user space. + +As of now, when a USB device is connected it is configured and +its interfaces are immediately made available to the users. With this +modification, only if root authorizes the device to be configured will +then it be possible to use it. + +Usage +===== + +Authorize a device to connect:: + + $ echo 1 > /sys/bus/usb/devices/DEVICE/authorized + +De-authorize a device:: + + $ echo 0 > /sys/bus/usb/devices/DEVICE/authorized + +Set new devices connected to hostX to be deauthorized by default (ie: +lock down):: + + $ echo 0 > /sys/bus/usb/devices/usbX/authorized_default + +Remove the lock down:: + + $ echo 1 > /sys/bus/usb/devices/usbX/authorized_default + +By default, all USB devices are authorized. Writing "2" to the +authorized_default attribute causes the kernel to authorize by default +only devices connected to internal USB ports. + + +Example system lockdown (lame) +------------------------------ + +Imagine you want to implement a lockdown so only devices of type XYZ +can be connected (for example, it is a kiosk machine with a visible +USB port):: + + boot up + rc.local -> + + for host in /sys/bus/usb/devices/usb* + do + echo 0 > $host/authorized_default + done + +Hookup an script to udev, for new USB devices:: + + if device_is_my_type $DEV + then + echo 1 > $device_path/authorized + done + + +Now, device_is_my_type() is where the juice for a lockdown is. Just +checking if the class, type and protocol match something is the worse +security verification you can make (or the best, for someone willing +to break it). If you need something secure, use crypto and Certificate +Authentication or stuff like that. Something simple for an storage key +could be:: + + function device_is_my_type() + { + echo 1 > authorized # temporarily authorize it + # FIXME: make sure none can mount it + mount DEVICENODE /mntpoint + sum=$(md5sum /mntpoint/.signature) + if [ $sum = $(cat /etc/lockdown/keysum) ] + then + echo "We are good, connected" + umount /mntpoint + # Other stuff so others can use it + else + echo 0 > authorized + fi + } + + +Of course, this is lame, you'd want to do a real certificate +verification stuff with PKI, so you don't depend on a shared secret, +etc, but you get the idea. Anybody with access to a device gadget kit +can fake descriptors and device info. Don't trust that. You are +welcome. + + +Interface authorization +----------------------- + +There is a similar approach to allow or deny specific USB interfaces. +That allows to block only a subset of an USB device. + +Authorize an interface:: + + $ echo 1 > /sys/bus/usb/devices/INTERFACE/authorized + +Deauthorize an interface:: + + $ echo 0 > /sys/bus/usb/devices/INTERFACE/authorized + +The default value for new interfaces +on a particular USB bus can be changed, too. + +Allow interfaces per default:: + + $ echo 1 > /sys/bus/usb/devices/usbX/interface_authorized_default + +Deny interfaces per default:: + + $ echo 0 > /sys/bus/usb/devices/usbX/interface_authorized_default + +Per default the interface_authorized_default bit is 1. +So all interfaces would authorized per default. + +Note: + If a deauthorized interface will be authorized so the driver probing must + be triggered manually by writing INTERFACE to /sys/bus/usb/drivers_probe + +For drivers that need multiple interfaces all needed interfaces should be +authorized first. After that the drivers should be probed. +This avoids side effects. -- cgit v1.3.1