From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- Documentation/driver-api/driver-model/bus.rst | 146 ++++++++++++++++++++++++++ 1 file changed, 146 insertions(+) create mode 100644 Documentation/driver-api/driver-model/bus.rst (limited to 'Documentation/driver-api/driver-model/bus.rst') diff --git a/Documentation/driver-api/driver-model/bus.rst b/Documentation/driver-api/driver-model/bus.rst new file mode 100644 index 000000000..9709ab62a --- /dev/null +++ b/Documentation/driver-api/driver-model/bus.rst @@ -0,0 +1,146 @@ +========= +Bus Types +========= + +Definition +~~~~~~~~~~ +See the kerneldoc for the struct bus_type. + +int bus_register(struct bus_type * bus); + + +Declaration +~~~~~~~~~~~ + +Each bus type in the kernel (PCI, USB, etc) should declare one static +object of this type. They must initialize the name field, and may +optionally initialize the match callback:: + + struct bus_type pci_bus_type = { + .name = "pci", + .match = pci_bus_match, + }; + +The structure should be exported to drivers in a header file: + +extern struct bus_type pci_bus_type; + + +Registration +~~~~~~~~~~~~ + +When a bus driver is initialized, it calls bus_register. This +initializes the rest of the fields in the bus object and inserts it +into a global list of bus types. Once the bus object is registered, +the fields in it are usable by the bus driver. + + +Callbacks +~~~~~~~~~ + +match(): Attaching Drivers to Devices +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The format of device ID structures and the semantics for comparing +them are inherently bus-specific. Drivers typically declare an array +of device IDs of devices they support that reside in a bus-specific +driver structure. + +The purpose of the match callback is to give the bus an opportunity to +determine if a particular driver supports a particular device by +comparing the device IDs the driver supports with the device ID of a +particular device, without sacrificing bus-specific functionality or +type-safety. + +When a driver is registered with the bus, the bus's list of devices is +iterated over, and the match callback is called for each device that +does not have a driver associated with it. + + + +Device and Driver Lists +~~~~~~~~~~~~~~~~~~~~~~~ + +The lists of devices and drivers are intended to replace the local +lists that many buses keep. They are lists of struct devices and +struct device_drivers, respectively. Bus drivers are free to use the +lists as they please, but conversion to the bus-specific type may be +necessary. + +The LDM core provides helper functions for iterating over each list:: + + int bus_for_each_dev(struct bus_type * bus, struct device * start, + void * data, + int (*fn)(struct device *, void *)); + + int bus_for_each_drv(struct bus_type * bus, struct device_driver * start, + void * data, int (*fn)(struct device_driver *, void *)); + +These helpers iterate over the respective list, and call the callback +for each device or driver in the list. All list accesses are +synchronized by taking the bus's lock (read currently). The reference +count on each object in the list is incremented before the callback is +called; it is decremented after the next object has been obtained. The +lock is not held when calling the callback. + + +sysfs +~~~~~~~~ +There is a top-level directory named 'bus'. + +Each bus gets a directory in the bus directory, along with two default +directories:: + + /sys/bus/pci/ + |-- devices + `-- drivers + +Drivers registered with the bus get a directory in the bus's drivers +directory:: + + /sys/bus/pci/ + |-- devices + `-- drivers + |-- Intel ICH + |-- Intel ICH Joystick + |-- agpgart + `-- e100 + +Each device that is discovered on a bus of that type gets a symlink in +the bus's devices directory to the device's directory in the physical +hierarchy:: + + /sys/bus/pci/ + |-- devices + | |-- 00:00.0 -> ../../../root/pci0/00:00.0 + | |-- 00:01.0 -> ../../../root/pci0/00:01.0 + | `-- 00:02.0 -> ../../../root/pci0/00:02.0 + `-- drivers + + +Exporting Attributes +~~~~~~~~~~~~~~~~~~~~ + +:: + + struct bus_attribute { + struct attribute attr; + ssize_t (*show)(const struct bus_type *, char * buf); + ssize_t (*store)(const struct bus_type *, const char * buf, size_t count); + }; + +Bus drivers can export attributes using the BUS_ATTR_RW macro that works +similarly to the DEVICE_ATTR_RW macro for devices. For example, a +definition like this:: + + static BUS_ATTR_RW(debug); + +is equivalent to declaring:: + + static bus_attribute bus_attr_debug; + +This can then be used to add and remove the attribute from the bus's +sysfs directory using:: + + int bus_create_file(struct bus_type *, struct bus_attribute *); + void bus_remove_file(struct bus_type *, struct bus_attribute *); -- cgit v1.3.1