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 --- lib/kunit/device.c | 201 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 201 insertions(+) create mode 100644 lib/kunit/device.c (limited to 'lib/kunit/device.c') diff --git a/lib/kunit/device.c b/lib/kunit/device.c new file mode 100644 index 000000000..85d57ad34 --- /dev/null +++ b/lib/kunit/device.c @@ -0,0 +1,201 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * KUnit-managed device implementation + * + * Implementation of struct kunit_device helpers for fake devices whose + * lifecycle is managed by KUnit. + * + * Copyright (C) 2023, Google LLC. + * Author: David Gow + */ + +#include +#include + +#include +#include +#include + +#include "device-impl.h" + +/* Wrappers for use with kunit_add_action() */ +KUNIT_DEFINE_ACTION_WRAPPER(device_unregister_wrapper, device_unregister, struct device *); +KUNIT_DEFINE_ACTION_WRAPPER(driver_unregister_wrapper, driver_unregister, struct device_driver *); + +/* The root device for the KUnit bus, parent of all kunit_devices. */ +static struct device *kunit_bus_device; + +/* A device owned by a KUnit test. */ +struct kunit_device { + struct device dev; + /* The KUnit test which owns this device. */ + struct kunit *owner; + /* If the driver is managed by KUnit and unique to this device. */ + const struct device_driver *driver; +}; + +#define to_kunit_device(d) container_of_const(d, struct kunit_device, dev) + +static const struct bus_type kunit_bus_type = { + .name = "kunit", +}; + +/* Register the 'kunit_bus' used for fake devices. */ +int kunit_bus_init(void) +{ + int error; + + kunit_bus_device = root_device_register("kunit"); + if (IS_ERR(kunit_bus_device)) + return PTR_ERR(kunit_bus_device); + + error = bus_register(&kunit_bus_type); + if (error) + root_device_unregister(kunit_bus_device); + return error; +} + +/* Unregister the 'kunit_bus' in case the KUnit module is unloaded. */ +void kunit_bus_shutdown(void) +{ + /* Make sure the bus exists before we unregister it. */ + if (IS_ERR_OR_NULL(kunit_bus_device)) + return; + + bus_unregister(&kunit_bus_type); + + root_device_unregister(kunit_bus_device); + + kunit_bus_device = NULL; +} + +/* Release a 'fake' KUnit device. */ +static void kunit_device_release(struct device *d) +{ + kfree(to_kunit_device(d)); +} + +/* + * Create and register a KUnit-managed struct device_driver on the kunit_bus. + * Returns an error pointer on failure. + */ +struct device_driver *kunit_driver_create(struct kunit *test, const char *name) +{ + struct device_driver *driver; + int err = -ENOMEM; + + driver = kunit_kzalloc(test, sizeof(*driver), GFP_KERNEL); + + if (!driver) + return ERR_PTR(err); + + driver->name = kunit_kstrdup_const(test, name, GFP_KERNEL); + driver->bus = &kunit_bus_type; + driver->owner = THIS_MODULE; + + err = driver_register(driver); + if (err) { + kunit_kfree(test, driver); + return ERR_PTR(err); + } + + kunit_add_action(test, driver_unregister_wrapper, driver); + return driver; +} +EXPORT_SYMBOL_GPL(kunit_driver_create); + +/* Helper which creates a kunit_device, attaches it to the kunit_bus*/ +static struct kunit_device *kunit_device_register_internal(struct kunit *test, + const char *name) +{ + struct kunit_device *kunit_dev; + int err = -ENOMEM; + + kunit_dev = kzalloc_obj(*kunit_dev); + if (!kunit_dev) + return ERR_PTR(err); + + kunit_dev->owner = test; + + err = dev_set_name(&kunit_dev->dev, "%s.%s", test->name, name); + if (err) { + kfree(kunit_dev); + return ERR_PTR(err); + } + + kunit_dev->dev.release = kunit_device_release; + kunit_dev->dev.bus = &kunit_bus_type; + kunit_dev->dev.parent = kunit_bus_device; + + err = device_register(&kunit_dev->dev); + if (err) { + put_device(&kunit_dev->dev); + return ERR_PTR(err); + } + + kunit_dev->dev.dma_mask = &kunit_dev->dev.coherent_dma_mask; + kunit_dev->dev.coherent_dma_mask = DMA_BIT_MASK(32); + + kunit_add_action(test, device_unregister_wrapper, &kunit_dev->dev); + + return kunit_dev; +} + +/* + * Create and register a new KUnit-managed device, using the user-supplied device_driver. + * On failure, returns an error pointer. + */ +struct device *kunit_device_register_with_driver(struct kunit *test, + const char *name, + const struct device_driver *drv) +{ + struct kunit_device *kunit_dev = kunit_device_register_internal(test, name); + + if (IS_ERR_OR_NULL(kunit_dev)) + return ERR_CAST(kunit_dev); + + return &kunit_dev->dev; +} +EXPORT_SYMBOL_GPL(kunit_device_register_with_driver); + +/* + * Create and register a new KUnit-managed device, including a matching device_driver. + * On failure, returns an error pointer. + */ +struct device *kunit_device_register(struct kunit *test, const char *name) +{ + struct device_driver *drv; + struct kunit_device *dev; + + drv = kunit_driver_create(test, name); + if (IS_ERR(drv)) + return ERR_CAST(drv); + + dev = kunit_device_register_internal(test, name); + if (IS_ERR(dev)) { + kunit_release_action(test, driver_unregister_wrapper, (void *)drv); + return ERR_CAST(dev); + } + + /* Request the driver be freed. */ + dev->driver = drv; + + + return &dev->dev; +} +EXPORT_SYMBOL_GPL(kunit_device_register); + +/* Unregisters a KUnit-managed device early (including the driver, if automatically created). */ +void kunit_device_unregister(struct kunit *test, struct device *dev) +{ + const struct device_driver *driver = to_kunit_device(dev)->driver; + + kunit_release_action(test, device_unregister_wrapper, dev); + if (driver) { + const char *driver_name = driver->name; + kunit_release_action(test, driver_unregister_wrapper, (void *)driver); + kunit_kfree_const(test, driver_name); + } +} +EXPORT_SYMBOL_GPL(kunit_device_unregister); + -- cgit v1.3.1