From 78004e9a87f240df03e2f73120d291763c32e0a7 Mon Sep 17 00:00:00 2001 From: Ali Ahmet Memis Date: Fri, 21 Aug 2026 01:45:27 +0000 Subject: openrisc: fix arbitrary kernel memory access via or1k_atomic syscall sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user pointers, v1 and v2, and swaps the words they point to in hand-written assembly. l.lwz r29,0(r4) l.lwz r27,0(r5) l.sw 0(r4),r27 l.sw 0(r5),r29 The pointers are not checked with access_ok(). The four memory accesses also have no exception table entries. A caller passes a kernel address as either pointer, and the syscall reads from and writes to it directly. This gives an unprivileged process a kernel read/write primitive. It overwrites kernel data such as the sys_call_table, gaining code execution in kernel context. Check both pointers before entering the critical section. Add fixups for the four memory accesses so faults on valid but unmapped user addresses return -EFAULT. [shorne@gmail.com: fix comment style] Fixes: 9d02a4283e9c ("OpenRISC: Boot code") Cc: stable@vger.kernel.org Signed-off-by: Ali Ahmet Memis Signed-off-by: Stafford Horne --- Documentation/driver-api/gpio/using-gpio.rst | 50 ++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 Documentation/driver-api/gpio/using-gpio.rst (limited to 'Documentation/driver-api/gpio/using-gpio.rst') diff --git a/Documentation/driver-api/gpio/using-gpio.rst b/Documentation/driver-api/gpio/using-gpio.rst new file mode 100644 index 000000000..894d88855 --- /dev/null +++ b/Documentation/driver-api/gpio/using-gpio.rst @@ -0,0 +1,50 @@ +========================= +Using GPIO Lines in Linux +========================= + +The Linux kernel exists to abstract and present hardware to users. GPIO lines +as such are normally not user facing abstractions. The most obvious, natural +and preferred way to use GPIO lines is to let kernel hardware drivers deal +with them. + +For examples of already existing generic drivers that will also be good +examples for any other kernel drivers you want to author, refer to +Documentation/driver-api/gpio/drivers-on-gpio.rst + +For any kind of mass produced system you want to support, such as servers, +laptops, phones, tablets, routers, and any consumer or office or business goods +using appropriate kernel drivers is paramount. Submit your code for inclusion +in the upstream Linux kernel when you feel it is mature enough and you will get +help to refine it, see Documentation/process/submitting-patches.rst. + +In Linux GPIO lines also have a userspace ABI. + +The userspace ABI is intended for one-off deployments. Examples are prototypes, +factory lines, maker community projects, workshop specimen, production tools, +industrial automation, PLC-type use cases, door controllers, in short a piece +of specialized equipment that is not produced by the numbers, requiring +operators to have a deep knowledge of the equipment and knows about the +software-hardware interface to be set up. They should not have a natural fit +to any existing kernel subsystem and not be a good fit for an operating system, +because of not being reusable or abstract enough, or involving a lot of non +computer hardware related policy. + +Applications that have a good reason to use the industrial I/O (IIO) subsystem +from userspace will likely be a good fit for using GPIO lines from userspace as +well. + +Do not under any circumstances abuse the GPIO userspace ABI to cut corners in +any product development projects. If you use it for prototyping, then do not +productify the prototype: rewrite it using proper kernel drivers. Do not under +any circumstances deploy any uniform products using GPIO from userspace. + +The userspace ABI is a character device for each GPIO hardware unit (GPIO chip). +These devices will appear on the system as ``/dev/gpiochip0`` thru +``/dev/gpiochipN``. Examples of how to directly use the userspace ABI can be +found in the kernel tree ``tools/gpio`` subdirectory. + +For structured and managed applications, we recommend that you make use of the +libgpiod_ library. This provides helper abstractions, command line utilities +and arbitration for multiple simultaneous consumers on the same GPIO chip. + +.. _libgpiod: https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/ -- cgit v1.3.1