x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

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) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 279 insertions, 0 deletions

diff --git a/init/init_task.c b/init/init_task.c
new file mode 100644
index 000000000..adb207cd9
--- /dev/null
+++ b/init/init_task.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/init_task.h>
+#include <linux/export.h>
+#include <linux/mqueue.h>
+#include <linux/sched.h>
+#include <linux/sched/sysctl.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/task.h>
+#include <linux/sched/ext.h>
+#include <linux/sched/exec_state.h>
+#include <linux/user_namespace.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/audit.h>
+#include <linux/numa.h>
+#include <linux/scs.h>
+#include <linux/plist.h>
+
+#include <linux/uaccess.h>
+
+static struct signal_struct init_signals = {
+	.nr_threads	= 1,
+	.thread_head	= LIST_HEAD_INIT(init_task.thread_node),
+	.wait_chldexit	= __WAIT_QUEUE_HEAD_INITIALIZER(init_signals.wait_chldexit),
+	.shared_pending	= {
+		.list = LIST_HEAD_INIT(init_signals.shared_pending.list),
+		.signal =  {{0}}
+	},
+	.multiprocess	= HLIST_HEAD_INIT,
+	.rlim		= INIT_RLIMITS,
+#ifdef CONFIG_CGROUPS
+	.cgroup_threadgroup_rwsem	= __RWSEM_INITIALIZER(init_signals.cgroup_threadgroup_rwsem),
+#endif
+	.cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex),
+	.exec_update_lock = __RWSEM_INITIALIZER(init_signals.exec_update_lock),
+#ifdef CONFIG_POSIX_TIMERS
+	.posix_timers		= HLIST_HEAD_INIT,
+	.ignored_posix_timers	= HLIST_HEAD_INIT,
+	.cputimer		= {
+		.cputime_atomic	= INIT_CPUTIME_ATOMIC,
+	},
+#endif
+	INIT_CPU_TIMERS(init_signals)
+	.pids = {
+		[PIDTYPE_PID]	= &init_struct_pid,
+		[PIDTYPE_TGID]	= &init_struct_pid,
+		[PIDTYPE_PGID]	= &init_struct_pid,
+		[PIDTYPE_SID]	= &init_struct_pid,
+	},
+	INIT_PREV_CPUTIME(init_signals)
+};
+
+static struct sighand_struct init_sighand = {
+	.count		= REFCOUNT_INIT(1),
+	.action		= { { { .sa_handler = SIG_DFL, } }, },
+	.siglock	= __SPIN_LOCK_UNLOCKED(init_sighand.siglock),
+	.signalfd_wqh	= __WAIT_QUEUE_HEAD_INITIALIZER(init_sighand.signalfd_wqh),
+};
+
+/* init to 2 - one for init_task, one to ensure it is never freed */
+struct task_exec_state init_task_exec_state = {
+	.count		= REFCOUNT_INIT(2),
+	.dumpable	= TASK_DUMPABLE_OWNER,
+	.user_ns	= &init_user_ns,
+};
+
+#ifdef CONFIG_SHADOW_CALL_STACK
+unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)] = {
+	[(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC
+};
+#endif
+
+/* init to 2 - one for init_task, one to ensure it is never freed */
+static struct group_info init_groups = { .usage = REFCOUNT_INIT(2) };
+
+/*
+ * The initial credentials for the initial task
+ */
+static struct cred init_cred = {
+	.usage			= ATOMIC_INIT(4),
+	.uid			= GLOBAL_ROOT_UID,
+	.gid			= GLOBAL_ROOT_GID,
+	.suid			= GLOBAL_ROOT_UID,
+	.sgid			= GLOBAL_ROOT_GID,
+	.euid			= GLOBAL_ROOT_UID,
+	.egid			= GLOBAL_ROOT_GID,
+	.fsuid			= GLOBAL_ROOT_UID,
+	.fsgid			= GLOBAL_ROOT_GID,
+	.securebits		= SECUREBITS_DEFAULT,
+	.cap_inheritable	= CAP_EMPTY_SET,
+	.cap_permitted		= CAP_FULL_SET,
+	.cap_effective		= CAP_FULL_SET,
+	.cap_bset		= CAP_FULL_SET,
+	.user			= INIT_USER,
+	.user_ns		= &init_user_ns,
+	.group_info		= &init_groups,
+	.ucounts		= &init_ucounts,
+};
+
+/*
+ * Set up the first task table, touch at your own risk!. Base=0,
+ * limit=0x1fffff (=2MB)
+ */
+struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+	.thread_info	= INIT_THREAD_INFO(init_task),
+	.stack_refcount	= REFCOUNT_INIT(1),
+#endif
+	.__state	= 0,
+	.stack		= init_stack,
+	.usage		= REFCOUNT_INIT(2),
+	.flags		= PF_KTHREAD,
+	.prio		= MAX_PRIO - 20,
+	.static_prio	= MAX_PRIO - 20,
+	.normal_prio	= MAX_PRIO - 20,
+	.policy		= SCHED_NORMAL,
+	.cpus_ptr	= &init_task.cpus_mask,
+	.user_cpus_ptr	= NULL,
+	.cpus_mask	= CPU_MASK_ALL,
+	.max_allowed_capacity	= SCHED_CAPACITY_SCALE,
+	.nr_cpus_allowed= NR_CPUS,
+	.mm		= NULL,
+	.active_mm	= &init_mm,
+	.exec_state	= &init_task_exec_state,
+	.restart_block	= {
+		.fn = do_no_restart_syscall,
+	},
+	.se		= {
+		.group_node 	= LIST_HEAD_INIT(init_task.se.group_node),
+	},
+	.rt		= {
+		.run_list	= LIST_HEAD_INIT(init_task.rt.run_list),
+		.time_slice	= RR_TIMESLICE,
+	},
+	.tasks		= LIST_HEAD_INIT(init_task.tasks),
+#ifdef CONFIG_SMP
+	.pushable_tasks	= PLIST_NODE_INIT(init_task.pushable_tasks, MAX_PRIO),
+#endif
+#ifdef CONFIG_CGROUP_SCHED
+	.sched_task_group = &root_task_group,
+#endif
+#ifdef CONFIG_SCHED_CLASS_EXT
+	.scx		= {
+		.dsq_list.node	= LIST_HEAD_INIT(init_task.scx.dsq_list.node),
+		.sticky_cpu	= -1,
+		.holding_cpu	= -1,
+		.runnable_cpu	= -1,
+		.runnable_node	= LIST_HEAD_INIT(init_task.scx.runnable_node),
+		.runnable_at	= INITIAL_JIFFIES,
+		.ddsp_dsq_id	= SCX_DSQ_INVALID,
+		.slice		= SCX_SLICE_DFL,
+	},
+#endif
+	.ptraced	= LIST_HEAD_INIT(init_task.ptraced),
+	.ptrace_entry	= LIST_HEAD_INIT(init_task.ptrace_entry),
+	.real_parent	= &init_task,
+	.parent		= &init_task,
+	.children	= LIST_HEAD_INIT(init_task.children),
+	.sibling	= LIST_HEAD_INIT(init_task.sibling),
+	.group_leader	= &init_task,
+	RCU_POINTER_INITIALIZER(real_cred, &init_cred),
+	RCU_POINTER_INITIALIZER(cred, &init_cred),
+	.comm		= INIT_TASK_COMM,
+	.thread		= INIT_THREAD,
+	.real_fs	= &init_fs,
+	.fs		= &init_fs,
+	.files		= &init_files,
+#ifdef CONFIG_IO_URING
+	.io_uring	= NULL,
+#endif
+	.signal		= &init_signals,
+	.sighand	= &init_sighand,
+	.nsproxy	= &init_nsproxy,
+	.pending	= {
+		.list = LIST_HEAD_INIT(init_task.pending.list),
+		.signal = {{0}}
+	},
+	.blocked	= {{0}},
+	.alloc_lock	= __SPIN_LOCK_UNLOCKED(init_task.alloc_lock),
+	.journal_info	= NULL,
+	INIT_CPU_TIMERS(init_task)
+	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
+	.blocked_lock	= __RAW_SPIN_LOCK_UNLOCKED(init_task.blocked_lock),
+	.timer_slack_ns = 50000, /* 50 usec default slack */
+	.thread_pid	= &init_struct_pid,
+	.thread_node	= LIST_HEAD_INIT(init_signals.thread_head),
+#ifdef CONFIG_AUDIT
+	.loginuid	= INVALID_UID,
+	.sessionid	= AUDIT_SID_UNSET,
+#endif
+#ifdef CONFIG_PERF_EVENTS
+	.perf_event_mutex = __MUTEX_INITIALIZER(init_task.perf_event_mutex),
+	.perf_event_list = LIST_HEAD_INIT(init_task.perf_event_list),
+#endif
+#ifdef CONFIG_PREEMPT_RCU
+	.rcu_read_lock_nesting = 0,
+	.rcu_read_unlock_special.s = 0,
+	.rcu_node_entry = LIST_HEAD_INIT(init_task.rcu_node_entry),
+	.rcu_blocked_node = NULL,
+#endif
+#ifdef CONFIG_TASKS_RCU
+	.rcu_tasks_holdout = false,
+	.rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list),
+	.rcu_tasks_idle_cpu = -1,
+	.rcu_tasks_exit_list = LIST_HEAD_INIT(init_task.rcu_tasks_exit_list),
+#endif
+#ifdef CONFIG_TASKS_TRACE_RCU
+	.trc_reader_nesting = 0,
+#endif
+#ifdef CONFIG_CPUSETS
+	.mems_allowed_seq = SEQCNT_SPINLOCK_ZERO(init_task.mems_allowed_seq,
+						 &init_task.alloc_lock),
+#endif
+	.blocked_donor = NULL,
+#ifdef CONFIG_RT_MUTEXES
+	.pi_waiters	= RB_ROOT_CACHED,
+	.pi_top_task	= NULL,
+#endif
+	INIT_PREV_CPUTIME(init_task)
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+	.vtime.seqcount	= SEQCNT_ZERO(init_task.vtime_seqcount),
+	.vtime.starttime = 0,
+	.vtime.state	= VTIME_SYS,
+#endif
+#ifdef CONFIG_NUMA_BALANCING
+	.numa_preferred_nid = NUMA_NO_NODE,
+	.numa_group	= NULL,
+	.numa_faults	= NULL,
+#endif
+#ifdef CONFIG_SCHED_CACHE
+	.preferred_llc  = -1,
+	.pref_llc_queued  = 0,
+#endif
+#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
+	.kasan_depth	= 1,
+#endif
+#ifdef CONFIG_KCSAN
+	.kcsan_ctx = {
+		.scoped_accesses	= {LIST_POISON1, NULL},
+	},
+#endif
+#ifdef CONFIG_TRACE_IRQFLAGS
+	.softirqs_enabled = 1,
+#endif
+#ifdef CONFIG_LOCKDEP
+	.lockdep_depth = 0, /* no locks held yet */
+	.curr_chain_key = INITIAL_CHAIN_KEY,
+	.lockdep_recursion = 0,
+#endif
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.ret_stack		= NULL,
+	.tracing_graph_pause	= ATOMIC_INIT(0),
+#endif
+#if defined(CONFIG_TRACING) && defined(CONFIG_PREEMPTION)
+	.trace_recursion = 0,
+#endif
+#ifdef CONFIG_LIVEPATCH
+	.patch_state	= KLP_TRANSITION_IDLE,
+#endif
+#ifdef CONFIG_SECURITY
+	.security	= NULL,
+#endif
+#ifdef CONFIG_SECCOMP_FILTER
+	.seccomp	= { .filter_count = ATOMIC_INIT(0) },
+#endif
+#ifdef CONFIG_SCHED_MM_CID
+	.mm_cid		= { .cid = MM_CID_UNSET, },
+#endif
+};
+EXPORT_SYMBOL(init_task);
+
+/*
+ * Initial thread structure. Alignment of this is handled by a special
+ * linker map entry.
+ */
+#ifndef CONFIG_THREAD_INFO_IN_TASK
+struct thread_info init_thread_info __init_thread_info = INIT_THREAD_INFO(init_task);
+#endif