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/i2c.rst | 48 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) create mode 100644 Documentation/driver-api/i2c.rst (limited to 'Documentation/driver-api/i2c.rst') diff --git a/Documentation/driver-api/i2c.rst b/Documentation/driver-api/i2c.rst new file mode 100644 index 000000000..7582c079d --- /dev/null +++ b/Documentation/driver-api/i2c.rst @@ -0,0 +1,48 @@ +I\ :sup:`2`\ C and SMBus Subsystem +================================== + +I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for +the "Inter-IC" bus, a simple bus protocol which is widely used where low +data rate communications suffice. Since it's also a licensed trademark, +some vendors use another name (such as "Two-Wire Interface", TWI) for +the same bus. I2C only needs two signals (SCL for clock, SDA for data), +conserving board real estate and minimizing signal quality issues. Most +I2C devices use seven bit addresses, and bus speeds of up to 400 kHz; +there's a high speed extension (3.4 MHz) that's not yet found wide use. +I2C is a multi-master bus; open drain signaling is used to arbitrate +between masters, as well as to handshake and to synchronize clocks from +slower clients. + +The Linux I2C programming interfaces support the master side of bus +interactions and the slave side. The programming interface is +structured around two kinds of driver, and two kinds of device. An I2C +"Adapter Driver" abstracts the controller hardware; it binds to a +physical device (perhaps a PCI device or platform_device) and exposes a +:c:type:`struct i2c_adapter ` representing each +I2C bus segment it manages. On each I2C bus segment will be I2C devices +represented by a :c:type:`struct i2c_client `. +Those devices will be bound to a :c:type:`struct i2c_driver +`, which should follow the standard Linux driver model. There +are functions to perform various I2C protocol operations; at this writing +all such functions are usable only from task context. + +The System Management Bus (SMBus) is a sibling protocol. Most SMBus +systems are also I2C conformant. The electrical constraints are tighter +for SMBus, and it standardizes particular protocol messages and idioms. +Controllers that support I2C can also support most SMBus operations, but +SMBus controllers don't support all the protocol options that an I2C +controller will. There are functions to perform various SMBus protocol +operations, either using I2C primitives or by issuing SMBus commands to +i2c_adapter devices which don't support those I2C operations. + +.. kernel-doc:: include/linux/i2c.h + :internal: + +.. kernel-doc:: drivers/i2c/i2c-boardinfo.c + :functions: i2c_register_board_info + +.. kernel-doc:: drivers/i2c/i2c-core-base.c + :export: + +.. kernel-doc:: drivers/i2c/i2c-core-smbus.c + :export: -- cgit v1.3.1