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 --- arch/um/drivers/ssl.c | 205 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 205 insertions(+) create mode 100644 arch/um/drivers/ssl.c (limited to 'arch/um/drivers/ssl.c') diff --git a/arch/um/drivers/ssl.c b/arch/um/drivers/ssl.c new file mode 100644 index 000000000..8006a5bd5 --- /dev/null +++ b/arch/um/drivers/ssl.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2000, 2002 Jeff Dike (jdike@karaya.com) + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include "chan.h" +#include +#include +#include "mconsole_kern.h" + +static const int ssl_version = 1; + +#define NR_PORTS 64 + +static void ssl_announce(char *dev_name, int dev) +{ + printk(KERN_INFO "Serial line %d assigned device '%s'\n", dev, + dev_name); +} + +/* Almost const, except that xterm_title may be changed in an initcall */ +static struct chan_opts opts = { + .announce = ssl_announce, + .xterm_title = "Serial Line #%d", + .raw = 1, +}; + +static int ssl_config(char *str, char **error_out); +static int ssl_get_config(char *dev, char *str, int size, char **error_out); +static int ssl_remove(int n, char **error_out); + + +/* Const, except for .mc.list */ +static struct line_driver driver = { + .name = "UML serial line", + .device_name = "ttyS", + .major = TTY_MAJOR, + .minor_start = 64, + .type = TTY_DRIVER_TYPE_SERIAL, + .subtype = 0, + .read_irq_name = "ssl", + .write_irq_name = "ssl-write", + .mc = { + .list = LIST_HEAD_INIT(driver.mc.list), + .name = "ssl", + .config = ssl_config, + .get_config = ssl_get_config, + .id = line_id, + .remove = ssl_remove, + }, +}; + +/* The array is initialized by line_init, at initcall time. The + * elements are locked individually as needed. + */ +static char *conf[NR_PORTS]; +static char *def_conf = CONFIG_SSL_CHAN; +static struct line serial_lines[NR_PORTS]; + +static int ssl_config(char *str, char **error_out) +{ + return line_config(serial_lines, ARRAY_SIZE(serial_lines), str, &opts, + error_out); +} + +static int ssl_get_config(char *dev, char *str, int size, char **error_out) +{ + return line_get_config(dev, serial_lines, ARRAY_SIZE(serial_lines), str, + size, error_out); +} + +static int ssl_remove(int n, char **error_out) +{ + return line_remove(serial_lines, ARRAY_SIZE(serial_lines), n, + error_out); +} + +static int ssl_install(struct tty_driver *driver, struct tty_struct *tty) +{ + return line_install(driver, tty, &serial_lines[tty->index]); +} + +static const struct tty_operations ssl_ops = { + .open = line_open, + .close = line_close, + .write = line_write, + .write_room = line_write_room, + .chars_in_buffer = line_chars_in_buffer, + .flush_buffer = line_flush_buffer, + .flush_chars = line_flush_chars, + .throttle = line_throttle, + .unthrottle = line_unthrottle, + .install = ssl_install, + .hangup = line_hangup, +}; + +/* Changed by ssl_init and referenced by ssl_exit, which are both serialized + * by being an initcall and exitcall, respectively. + */ +static int ssl_init_done; + +static void ssl_console_write(struct console *c, const char *string, + unsigned len) +{ + struct line *line = &serial_lines[c->index]; + unsigned long flags; + + spin_lock_irqsave(&line->lock, flags); + console_write_chan(line->chan_out, string, len); + spin_unlock_irqrestore(&line->lock, flags); +} + +static struct tty_driver *ssl_console_device(struct console *c, int *index) +{ + *index = c->index; + return driver.driver; +} + +static int ssl_console_setup(struct console *co, char *options) +{ + struct line *line = &serial_lines[co->index]; + + return console_open_chan(line, co); +} + +/* No locking for register_console call - relies on single-threaded initcalls */ +static struct console ssl_cons = { + .name = "ttyS", + .write = ssl_console_write, + .device = ssl_console_device, + .setup = ssl_console_setup, + .flags = CON_PRINTBUFFER|CON_ANYTIME, + .index = -1, +}; + +static int ssl_init(void) +{ + char *new_title; + int err; + int i; + + printk(KERN_INFO "Initializing software serial port version %d\n", + ssl_version); + + err = register_lines(&driver, &ssl_ops, serial_lines, + ARRAY_SIZE(serial_lines)); + if (err) + return err; + + new_title = add_xterm_umid(opts.xterm_title); + if (new_title != NULL) + opts.xterm_title = new_title; + + for (i = 0; i < NR_PORTS; i++) { + char *error; + char *s = conf[i]; + if (!s) + s = def_conf; + if (setup_one_line(serial_lines, i, s, &opts, &error)) + printk(KERN_ERR "setup_one_line failed for " + "device %d : %s\n", i, error); + } + + ssl_init_done = 1; + register_console(&ssl_cons); + return 0; +} +late_initcall(ssl_init); + +static void ssl_exit(void) +{ + if (!ssl_init_done) + return; + close_lines(serial_lines, ARRAY_SIZE(serial_lines)); +} +__uml_exitcall(ssl_exit); + +static int ssl_chan_setup(char *str) +{ + line_setup(conf, NR_PORTS, &def_conf, str, "serial line"); + return 1; +} + +__setup("ssl", ssl_chan_setup); +__channel_help(ssl_chan_setup, "ssl"); + +static int ssl_non_raw_setup(char *str) +{ + opts.raw = 0; + return 1; +} +__setup("ssl-non-raw", ssl_non_raw_setup); +__uml_help(ssl_non_raw_setup, +"ssl-non-raw\n" +" Set serial lines to non-raw mode.\n\n" +); -- cgit v1.3.1