From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- samples/kprobes/Makefile | 6 ++ samples/kprobes/kprobe_example.c | 129 ++++++++++++++++++++++++++++++++++++ samples/kprobes/kretprobe_example.c | 108 ++++++++++++++++++++++++++++++ 3 files changed, 243 insertions(+) create mode 100644 samples/kprobes/Makefile create mode 100644 samples/kprobes/kprobe_example.c create mode 100644 samples/kprobes/kretprobe_example.c (limited to 'samples/kprobes') diff --git a/samples/kprobes/Makefile b/samples/kprobes/Makefile new file mode 100644 index 000000000..e77459271 --- /dev/null +++ b/samples/kprobes/Makefile @@ -0,0 +1,6 @@ +# SPDX-License-Identifier: GPL-2.0-only +# builds the kprobes example kernel modules; +# then to use one (as root): insmod + +obj-$(CONFIG_SAMPLE_KPROBES) += kprobe_example.o +obj-$(CONFIG_SAMPLE_KRETPROBES) += kretprobe_example.o diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c new file mode 100644 index 000000000..53ec6c8b8 --- /dev/null +++ b/samples/kprobes/kprobe_example.c @@ -0,0 +1,129 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Here's a sample kernel module showing the use of kprobes to dump a + * stack trace and selected registers when kernel_clone() is called. + * + * For more information on theory of operation of kprobes, see + * Documentation/trace/kprobes.rst + * + * You will see the trace data in /var/log/messages and on the console + * whenever kernel_clone() is invoked to create a new process. + */ + +#define pr_fmt(fmt) "%s: " fmt, __func__ + +#include +#include +#include + +static char symbol[KSYM_NAME_LEN] = "kernel_clone"; +module_param_string(symbol, symbol, KSYM_NAME_LEN, 0644); + +/* For each probe you need to allocate a kprobe structure */ +static struct kprobe kp = { + .symbol_name = symbol, +}; + +/* kprobe pre_handler: called just before the probed instruction is executed */ +static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs) +{ +#ifdef CONFIG_X86 + pr_info("<%s> p->addr = 0x%p, ip = %lx, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->ip, regs->flags); +#endif +#ifdef CONFIG_PPC + pr_info("<%s> p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n", + p->symbol_name, p->addr, regs->nip, regs->msr); +#endif +#ifdef CONFIG_MIPS + pr_info("<%s> p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n", + p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); +#endif +#ifdef CONFIG_ARM64 + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, pstate = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); +#endif +#ifdef CONFIG_ARM + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, cpsr = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->ARM_pc, (long)regs->ARM_cpsr); +#endif +#ifdef CONFIG_RISCV + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, status = 0x%lx\n", + p->symbol_name, p->addr, regs->epc, regs->status); +#endif +#ifdef CONFIG_S390 + pr_info("<%s> p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->psw.addr, regs->flags); +#endif +#ifdef CONFIG_LOONGARCH + pr_info("<%s> p->addr = 0x%p, era = 0x%lx, estat = 0x%lx\n", + p->symbol_name, p->addr, regs->csr_era, regs->csr_estat); +#endif + + /* A dump_stack() here will give a stack backtrace */ + return 0; +} + +/* kprobe post_handler: called after the probed instruction is executed */ +static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs, + unsigned long flags) +{ +#ifdef CONFIG_X86 + pr_info("<%s> p->addr = 0x%p, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->flags); +#endif +#ifdef CONFIG_PPC + pr_info("<%s> p->addr = 0x%p, msr = 0x%lx\n", + p->symbol_name, p->addr, regs->msr); +#endif +#ifdef CONFIG_MIPS + pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n", + p->symbol_name, p->addr, regs->cp0_status); +#endif +#ifdef CONFIG_ARM64 + pr_info("<%s> p->addr = 0x%p, pstate = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->pstate); +#endif +#ifdef CONFIG_ARM + pr_info("<%s> p->addr = 0x%p, cpsr = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->ARM_cpsr); +#endif +#ifdef CONFIG_RISCV + pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n", + p->symbol_name, p->addr, regs->status); +#endif +#ifdef CONFIG_S390 + pr_info("<%s> p->addr, 0x%p, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->flags); +#endif +#ifdef CONFIG_LOONGARCH + pr_info("<%s> p->addr = 0x%p, estat = 0x%lx\n", + p->symbol_name, p->addr, regs->csr_estat); +#endif +} + +static int __init kprobe_init(void) +{ + int ret; + kp.pre_handler = handler_pre; + kp.post_handler = handler_post; + + ret = register_kprobe(&kp); + if (ret < 0) { + pr_err("register_kprobe failed, returned %d\n", ret); + return ret; + } + pr_info("Planted kprobe at %p\n", kp.addr); + return 0; +} + +static void __exit kprobe_exit(void) +{ + unregister_kprobe(&kp); + pr_info("kprobe at %p unregistered\n", kp.addr); +} + +module_init(kprobe_init) +module_exit(kprobe_exit) +MODULE_DESCRIPTION("sample kernel module showing the use of kprobes"); +MODULE_LICENSE("GPL"); diff --git a/samples/kprobes/kretprobe_example.c b/samples/kprobes/kretprobe_example.c new file mode 100644 index 000000000..65d6dcafd --- /dev/null +++ b/samples/kprobes/kretprobe_example.c @@ -0,0 +1,108 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * kretprobe_example.c + * + * Here's a sample kernel module showing the use of return probes to + * report the return value and total time taken for probed function + * to run. + * + * usage: insmod kretprobe_example.ko func= + * + * If no func_name is specified, kernel_clone is instrumented + * + * For more information on theory of operation of kretprobes, see + * Documentation/trace/kprobes.rst + * + * Build and insert the kernel module as done in the kprobe example. + * You will see the trace data in /var/log/messages and on the console + * whenever the probed function returns. (Some messages may be suppressed + * if syslogd is configured to eliminate duplicate messages.) + */ + +#include +#include +#include +#include +#include + +static char func_name[KSYM_NAME_LEN] = "kernel_clone"; +module_param_string(func, func_name, KSYM_NAME_LEN, 0644); +MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the" + " function's execution time"); + +/* per-instance private data */ +struct my_data { + ktime_t entry_stamp; +}; + +/* Here we use the entry_handler to timestamp function entry */ +static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) +{ + struct my_data *data; + + if (!current->mm) + return 1; /* Skip kernel threads */ + + data = (struct my_data *)ri->data; + data->entry_stamp = ktime_get(); + return 0; +} +NOKPROBE_SYMBOL(entry_handler); + +/* + * Return-probe handler: Log the return value and duration. Duration may turn + * out to be zero consistently, depending upon the granularity of time + * accounting on the platform. + */ +static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) +{ + unsigned long retval = regs_return_value(regs); + struct my_data *data = (struct my_data *)ri->data; + s64 delta; + ktime_t now; + + now = ktime_get(); + delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); + pr_info("%s returned %lu and took %lld ns to execute\n", + func_name, retval, (long long)delta); + return 0; +} +NOKPROBE_SYMBOL(ret_handler); + +static struct kretprobe my_kretprobe = { + .handler = ret_handler, + .entry_handler = entry_handler, + .data_size = sizeof(struct my_data), + /* Probe up to 20 instances concurrently. */ + .maxactive = 20, +}; + +static int __init kretprobe_init(void) +{ + int ret; + + my_kretprobe.kp.symbol_name = func_name; + ret = register_kretprobe(&my_kretprobe); + if (ret < 0) { + pr_err("register_kretprobe failed, returned %d\n", ret); + return ret; + } + pr_info("Planted return probe at %s: %p\n", + my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); + return 0; +} + +static void __exit kretprobe_exit(void) +{ + unregister_kretprobe(&my_kretprobe); + pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); + + /* nmissed > 0 suggests that maxactive was set too low. */ + pr_info("Missed probing %d instances of %s\n", + my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); +} + +module_init(kretprobe_init) +module_exit(kretprobe_exit) +MODULE_DESCRIPTION("sample kernel module showing the use of return probes"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1