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/rtc/rtc-ntxec.c | 145 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 145 insertions(+) create mode 100644 drivers/rtc/rtc-ntxec.c (limited to 'drivers/rtc/rtc-ntxec.c') diff --git a/drivers/rtc/rtc-ntxec.c b/drivers/rtc/rtc-ntxec.c new file mode 100644 index 000000000..d28ddb34e --- /dev/null +++ b/drivers/rtc/rtc-ntxec.c @@ -0,0 +1,145 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * The Netronix embedded controller is a microcontroller found in some + * e-book readers designed by the original design manufacturer Netronix, Inc. + * It contains RTC, battery monitoring, system power management, and PWM + * functionality. + * + * This driver implements access to the RTC time and date. + * + * Copyright 2020 Jonathan Neuschäfer + */ + +#include +#include +#include +#include +#include +#include + +struct ntxec_rtc { + struct device *dev; + struct ntxec *ec; +}; + +#define NTXEC_REG_WRITE_YEAR 0x10 +#define NTXEC_REG_WRITE_MONTH 0x11 +#define NTXEC_REG_WRITE_DAY 0x12 +#define NTXEC_REG_WRITE_HOUR 0x13 +#define NTXEC_REG_WRITE_MINUTE 0x14 +#define NTXEC_REG_WRITE_SECOND 0x15 + +#define NTXEC_REG_READ_YEAR_MONTH 0x20 +#define NTXEC_REG_READ_MDAY_HOUR 0x21 +#define NTXEC_REG_READ_MINUTE_SECOND 0x23 + +static int ntxec_read_time(struct device *dev, struct rtc_time *tm) +{ + struct ntxec_rtc *rtc = dev_get_drvdata(dev); + unsigned int value; + int res; + +retry: + res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MINUTE_SECOND, &value); + if (res < 0) + return res; + + tm->tm_min = value >> 8; + tm->tm_sec = value & 0xff; + + res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MDAY_HOUR, &value); + if (res < 0) + return res; + + tm->tm_mday = value >> 8; + tm->tm_hour = value & 0xff; + + res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_YEAR_MONTH, &value); + if (res < 0) + return res; + + tm->tm_year = (value >> 8) + 100; + tm->tm_mon = (value & 0xff) - 1; + + /* + * Read the minutes/seconds field again. If it changed since the first + * read, we can't assume that the values read so far are consistent, + * and should start from the beginning. + */ + res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MINUTE_SECOND, &value); + if (res < 0) + return res; + + if (tm->tm_min != value >> 8 || tm->tm_sec != (value & 0xff)) + goto retry; + + return 0; +} + +static int ntxec_set_time(struct device *dev, struct rtc_time *tm) +{ + struct ntxec_rtc *rtc = dev_get_drvdata(dev); + + /* + * To avoid time overflows while we're writing the full date/time, + * set the seconds field to zero before doing anything else. For the + * next 59 seconds (plus however long it takes until the RTC's next + * update of the second field), the seconds field will not overflow + * into the other fields. + */ + struct reg_sequence regs[] = { + { NTXEC_REG_WRITE_SECOND, ntxec_reg8(0) }, + { NTXEC_REG_WRITE_YEAR, ntxec_reg8(tm->tm_year - 100) }, + { NTXEC_REG_WRITE_MONTH, ntxec_reg8(tm->tm_mon + 1) }, + { NTXEC_REG_WRITE_DAY, ntxec_reg8(tm->tm_mday) }, + { NTXEC_REG_WRITE_HOUR, ntxec_reg8(tm->tm_hour) }, + { NTXEC_REG_WRITE_MINUTE, ntxec_reg8(tm->tm_min) }, + { NTXEC_REG_WRITE_SECOND, ntxec_reg8(tm->tm_sec) }, + }; + + return regmap_multi_reg_write(rtc->ec->regmap, regs, ARRAY_SIZE(regs)); +} + +static const struct rtc_class_ops ntxec_rtc_ops = { + .read_time = ntxec_read_time, + .set_time = ntxec_set_time, +}; + +static int ntxec_rtc_probe(struct platform_device *pdev) +{ + struct rtc_device *dev; + struct ntxec_rtc *rtc; + + device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent); + + rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL); + if (!rtc) + return -ENOMEM; + + rtc->dev = &pdev->dev; + rtc->ec = dev_get_drvdata(pdev->dev.parent); + platform_set_drvdata(pdev, rtc); + + dev = devm_rtc_allocate_device(&pdev->dev); + if (IS_ERR(dev)) + return PTR_ERR(dev); + + dev->ops = &ntxec_rtc_ops; + dev->range_min = RTC_TIMESTAMP_BEGIN_2000; + dev->range_max = 9025257599LL; /* 2255-12-31 23:59:59 */ + + return devm_rtc_register_device(dev); +} + +static struct platform_driver ntxec_rtc_driver = { + .driver = { + .name = "ntxec-rtc", + }, + .probe = ntxec_rtc_probe, +}; +module_platform_driver(ntxec_rtc_driver); + +MODULE_AUTHOR("Jonathan Neuschäfer "); +MODULE_DESCRIPTION("RTC driver for Netronix EC"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("platform:ntxec-rtc"); -- cgit v1.3.1