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 --- drivers/cpufreq/virtual-cpufreq.c | 329 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 329 insertions(+) create mode 100644 drivers/cpufreq/virtual-cpufreq.c (limited to 'drivers/cpufreq/virtual-cpufreq.c') diff --git a/drivers/cpufreq/virtual-cpufreq.c b/drivers/cpufreq/virtual-cpufreq.c new file mode 100644 index 000000000..dc78b7440 --- /dev/null +++ b/drivers/cpufreq/virtual-cpufreq.c @@ -0,0 +1,329 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2024 Google LLC + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * CPU0..CPUn + * +-------------+-------------------------------+--------+-------+ + * | Register | Description | Offset | Len | + * +-------------+-------------------------------+--------+-------+ + * | cur_perf | read this register to get | 0x0 | 0x4 | + * | | the current perf (integer val | | | + * | | representing perf relative to | | | + * | | max performance) | | | + * | | that vCPU is running at | | | + * +-------------+-------------------------------+--------+-------+ + * | set_perf | write to this register to set | 0x4 | 0x4 | + * | | perf value of the vCPU | | | + * +-------------+-------------------------------+--------+-------+ + * | perftbl_len | number of entries in perf | 0x8 | 0x4 | + * | | table. A single entry in the | | | + * | | perf table denotes no table | | | + * | | and the entry contains | | | + * | | the maximum perf value | | | + * | | that this vCPU supports. | | | + * | | The guest can request any | | | + * | | value between 1 and max perf | | | + * | | when perftbls are not used. | | | + * +---------------------------------------------+--------+-------+ + * | perftbl_sel | write to this register to | 0xc | 0x4 | + * | | select perf table entry to | | | + * | | read from | | | + * +---------------------------------------------+--------+-------+ + * | perftbl_rd | read this register to get | 0x10 | 0x4 | + * | | perf value of the selected | | | + * | | entry based on perftbl_sel | | | + * +---------------------------------------------+--------+-------+ + * | perf_domain | performance domain number | 0x14 | 0x4 | + * | | that this vCPU belongs to. | | | + * | | vCPUs sharing the same perf | | | + * | | domain number are part of the | | | + * | | same performance domain. | | | + * +-------------+-------------------------------+--------+-------+ + */ + +#define REG_CUR_PERF_STATE_OFFSET 0x0 +#define REG_SET_PERF_STATE_OFFSET 0x4 +#define REG_PERFTBL_LEN_OFFSET 0x8 +#define REG_PERFTBL_SEL_OFFSET 0xc +#define REG_PERFTBL_RD_OFFSET 0x10 +#define REG_PERF_DOMAIN_OFFSET 0x14 +#define PER_CPU_OFFSET 0x1000 + +#define PERFTBL_MAX_ENTRIES 64U + +static void __iomem *base; +static DEFINE_PER_CPU(u32, perftbl_num_entries); + +static void virt_scale_freq_tick(void) +{ + int cpu = smp_processor_id(); + u32 max_freq = (u32)cpufreq_get_hw_max_freq(cpu); + u64 cur_freq; + unsigned long scale; + + cur_freq = (u64)readl_relaxed(base + cpu * PER_CPU_OFFSET + + REG_CUR_PERF_STATE_OFFSET); + + cur_freq <<= SCHED_CAPACITY_SHIFT; + scale = (unsigned long)div_u64(cur_freq, max_freq); + scale = min(scale, SCHED_CAPACITY_SCALE); + + this_cpu_write(arch_freq_scale, scale); +} + +static struct scale_freq_data virt_sfd = { + .source = SCALE_FREQ_SOURCE_VIRT, + .set_freq_scale = virt_scale_freq_tick, +}; + +static unsigned int virt_cpufreq_set_perf(struct cpufreq_policy *policy, + unsigned int target_freq) +{ + writel_relaxed(target_freq, + base + policy->cpu * PER_CPU_OFFSET + REG_SET_PERF_STATE_OFFSET); + return 0; +} + +static unsigned int virt_cpufreq_fast_switch(struct cpufreq_policy *policy, + unsigned int target_freq) +{ + virt_cpufreq_set_perf(policy, target_freq); + return target_freq; +} + +static u32 virt_cpufreq_get_perftbl_entry(int cpu, u32 idx) +{ + writel_relaxed(idx, base + cpu * PER_CPU_OFFSET + + REG_PERFTBL_SEL_OFFSET); + return readl_relaxed(base + cpu * PER_CPU_OFFSET + + REG_PERFTBL_RD_OFFSET); +} + +static int virt_cpufreq_target(struct cpufreq_policy *policy, + unsigned int target_freq, + unsigned int relation) +{ + struct cpufreq_freqs freqs; + int ret = 0; + + freqs.old = policy->cur; + freqs.new = target_freq; + + cpufreq_freq_transition_begin(policy, &freqs); + ret = virt_cpufreq_set_perf(policy, target_freq); + cpufreq_freq_transition_end(policy, &freqs, ret != 0); + + return ret; +} + +static int virt_cpufreq_get_sharing_cpus(struct cpufreq_policy *policy) +{ + u32 cur_perf_domain, perf_domain; + struct device *cpu_dev; + int cpu; + + cur_perf_domain = readl_relaxed(base + policy->cpu * + PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET); + + for_each_present_cpu(cpu) { + cpu_dev = get_cpu_device(cpu); + if (!cpu_dev) + continue; + + perf_domain = readl_relaxed(base + cpu * + PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET); + + if (perf_domain == cur_perf_domain) + cpumask_set_cpu(cpu, policy->cpus); + } + + return 0; +} + +static int virt_cpufreq_get_freq_info(struct cpufreq_policy *policy) +{ + struct cpufreq_frequency_table *table; + u32 num_perftbl_entries, idx; + + num_perftbl_entries = per_cpu(perftbl_num_entries, policy->cpu); + + if (num_perftbl_entries == 1) { + policy->cpuinfo.min_freq = 1; + policy->cpuinfo.max_freq = virt_cpufreq_get_perftbl_entry(policy->cpu, 0); + + policy->cur = policy->cpuinfo.max_freq; + return 0; + } + + table = kzalloc_objs(*table, num_perftbl_entries + 1); + if (!table) + return -ENOMEM; + + for (idx = 0; idx < num_perftbl_entries; idx++) + table[idx].frequency = virt_cpufreq_get_perftbl_entry(policy->cpu, idx); + + table[idx].frequency = CPUFREQ_TABLE_END; + policy->freq_table = table; + + return 0; +} + +static int virt_cpufreq_cpu_init(struct cpufreq_policy *policy) +{ + struct device *cpu_dev; + int ret; + + cpu_dev = get_cpu_device(policy->cpu); + if (!cpu_dev) + return -ENODEV; + + ret = virt_cpufreq_get_freq_info(policy); + if (ret) { + dev_warn(cpu_dev, "failed to get cpufreq info\n"); + return ret; + } + + ret = virt_cpufreq_get_sharing_cpus(policy); + if (ret) { + dev_warn(cpu_dev, "failed to get sharing cpumask\n"); + return ret; + } + + /* + * To simplify and improve latency of handling frequency requests on + * the host side, this ensures that the vCPU thread triggering the MMIO + * abort is the same thread whose performance constraints (Ex. uclamp + * settings) need to be updated. This simplifies the VMM (Virtual + * Machine Manager) having to find the correct vCPU thread and/or + * facing permission issues when configuring other threads. + */ + policy->dvfs_possible_from_any_cpu = false; + policy->fast_switch_possible = true; + + /* + * Using the default SCALE_FREQ_SOURCE_CPUFREQ is insufficient since + * the actual physical CPU frequency may not match requested frequency + * from the vCPU thread due to frequency update latencies or other + * inputs to the physical CPU frequency selection. This additional FIE + * source allows for more accurate freq_scale updates and only takes + * effect if another FIE source such as AMUs have not been registered. + */ + topology_set_scale_freq_source(&virt_sfd, policy->cpus); + + return 0; +} + +static void virt_cpufreq_cpu_exit(struct cpufreq_policy *policy) +{ + topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_VIRT, policy->related_cpus); + kfree(policy->freq_table); +} + +static int virt_cpufreq_online(struct cpufreq_policy *policy) +{ + /* Nothing to restore. */ + return 0; +} + +static int virt_cpufreq_offline(struct cpufreq_policy *policy) +{ + /* Dummy offline() to avoid exit() being called and freeing resources. */ + return 0; +} + +static int virt_cpufreq_verify_policy(struct cpufreq_policy_data *policy) +{ + if (policy->freq_table) + return cpufreq_frequency_table_verify(policy); + + cpufreq_verify_within_cpu_limits(policy); + return 0; +} + +static struct cpufreq_driver cpufreq_virt_driver = { + .name = "virt-cpufreq", + .init = virt_cpufreq_cpu_init, + .exit = virt_cpufreq_cpu_exit, + .online = virt_cpufreq_online, + .offline = virt_cpufreq_offline, + .verify = virt_cpufreq_verify_policy, + .target = virt_cpufreq_target, + .fast_switch = virt_cpufreq_fast_switch, +}; + +static int virt_cpufreq_driver_probe(struct platform_device *pdev) +{ + u32 num_perftbl_entries; + int ret, cpu; + + base = devm_platform_ioremap_resource(pdev, 0); + if (IS_ERR(base)) + return PTR_ERR(base); + + for_each_possible_cpu(cpu) { + num_perftbl_entries = readl_relaxed(base + cpu * PER_CPU_OFFSET + + REG_PERFTBL_LEN_OFFSET); + + if (!num_perftbl_entries || num_perftbl_entries > PERFTBL_MAX_ENTRIES) + return -ENODEV; + + per_cpu(perftbl_num_entries, cpu) = num_perftbl_entries; + } + + ret = cpufreq_register_driver(&cpufreq_virt_driver); + if (ret) { + dev_err(&pdev->dev, "Virtual CPUFreq driver failed to register: %d\n", ret); + return ret; + } + + dev_dbg(&pdev->dev, "Virtual CPUFreq driver initialized\n"); + return 0; +} + +static void virt_cpufreq_driver_remove(struct platform_device *pdev) +{ + cpufreq_unregister_driver(&cpufreq_virt_driver); +} + +static const struct of_device_id virt_cpufreq_match[] = { + { .compatible = "qemu,virtual-cpufreq", .data = NULL}, + {} +}; +MODULE_DEVICE_TABLE(of, virt_cpufreq_match); + +static struct platform_driver virt_cpufreq_driver = { + .probe = virt_cpufreq_driver_probe, + .remove = virt_cpufreq_driver_remove, + .driver = { + .name = "virt-cpufreq", + .of_match_table = virt_cpufreq_match, + }, +}; + +static int __init virt_cpufreq_init(void) +{ + return platform_driver_register(&virt_cpufreq_driver); +} +postcore_initcall(virt_cpufreq_init); + +static void __exit virt_cpufreq_exit(void) +{ + platform_driver_unregister(&virt_cpufreq_driver); +} +module_exit(virt_cpufreq_exit); + +MODULE_DESCRIPTION("Virtual cpufreq driver"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1