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, 306 insertions, 0 deletions

diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c
new file mode 100644
index 000000000..84cb527f5
--- /dev/null
+++ b/drivers/ptp/ptp_vclock.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PTP virtual clock driver
+ *
+ * Copyright 2021 NXP
+ */
+#include <linux/slab.h>
+#include <linux/hashtable.h>
+#include "ptp_private.h"
+
+#define PTP_VCLOCK_CC_SHIFT		31
+#define PTP_VCLOCK_CC_MULT		(1 << PTP_VCLOCK_CC_SHIFT)
+#define PTP_VCLOCK_FADJ_SHIFT		9
+#define PTP_VCLOCK_FADJ_DENOMINATOR	15625ULL
+#define PTP_VCLOCK_REFRESH_INTERVAL	(HZ * 2)
+
+/* protects vclock_hash addition/deletion */
+static DEFINE_SPINLOCK(vclock_hash_lock);
+
+static DEFINE_READ_MOSTLY_HASHTABLE(vclock_hash, 8);
+
+DEFINE_STATIC_SRCU(vclock_srcu);
+
+static void ptp_vclock_hash_add(struct ptp_vclock *vclock)
+{
+	spin_lock(&vclock_hash_lock);
+
+	hlist_add_head_rcu(&vclock->vclock_hash_node,
+			   &vclock_hash[vclock->clock->index % HASH_SIZE(vclock_hash)]);
+
+	spin_unlock(&vclock_hash_lock);
+}
+
+static void ptp_vclock_hash_del(struct ptp_vclock *vclock)
+{
+	spin_lock(&vclock_hash_lock);
+
+	hlist_del_init_rcu(&vclock->vclock_hash_node);
+
+	spin_unlock(&vclock_hash_lock);
+
+	synchronize_srcu(&vclock_srcu);
+}
+
+static int ptp_vclock_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	s64 adj;
+
+	adj = (s64)scaled_ppm << PTP_VCLOCK_FADJ_SHIFT;
+	adj = div_s64(adj, PTP_VCLOCK_FADJ_DENOMINATOR);
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	timecounter_read(&vclock->tc);
+	vclock->cc.mult = PTP_VCLOCK_CC_MULT + adj;
+	mutex_unlock(&vclock->lock);
+
+	return 0;
+}
+
+static int ptp_vclock_adjtime(struct ptp_clock_info *ptp, s64 delta)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	timecounter_adjtime(&vclock->tc, delta);
+	mutex_unlock(&vclock->lock);
+
+	return 0;
+}
+
+static int ptp_vclock_gettime(struct ptp_clock_info *ptp,
+			      struct timespec64 *ts)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	u64 ns;
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	ns = timecounter_read(&vclock->tc);
+	mutex_unlock(&vclock->lock);
+	*ts = ns_to_timespec64(ns);
+
+	return 0;
+}
+
+static int ptp_vclock_gettimex(struct ptp_clock_info *ptp,
+			       struct timespec64 *ts,
+			       struct ptp_system_timestamp *sts)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	struct ptp_clock *pptp = vclock->pclock;
+	struct timespec64 pts;
+	int err;
+	u64 ns;
+
+	err = pptp->info->getcyclesx64(pptp->info, &pts, sts);
+	if (err)
+		return err;
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	ns = timecounter_cyc2time(&vclock->tc, timespec64_to_ns(&pts));
+	mutex_unlock(&vclock->lock);
+
+	*ts = ns_to_timespec64(ns);
+
+	return 0;
+}
+
+static int ptp_vclock_settime(struct ptp_clock_info *ptp,
+			      const struct timespec64 *ts)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	u64 ns = timespec64_to_ns(ts);
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	timecounter_init(&vclock->tc, &vclock->cc, ns);
+	mutex_unlock(&vclock->lock);
+
+	return 0;
+}
+
+static int ptp_vclock_getcrosststamp(struct ptp_clock_info *ptp,
+				     struct system_device_crosststamp *xtstamp)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	struct ptp_clock *pptp = vclock->pclock;
+	int err;
+	u64 ns;
+
+	err = pptp->info->getcrosscycles(pptp->info, xtstamp);
+	if (err)
+		return err;
+
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
+	ns = timecounter_cyc2time(&vclock->tc, ktime_to_ns(xtstamp->device));
+	mutex_unlock(&vclock->lock);
+
+	xtstamp->device = ns_to_ktime(ns);
+
+	return 0;
+}
+
+static long ptp_vclock_refresh(struct ptp_clock_info *ptp)
+{
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	struct timespec64 ts;
+
+	ptp_vclock_gettime(&vclock->info, &ts);
+
+	return PTP_VCLOCK_REFRESH_INTERVAL;
+}
+
+static void ptp_vclock_set_subclass(struct ptp_clock *ptp)
+{
+	lockdep_set_subclass(&ptp->clock.rwsem, PTP_LOCK_VIRTUAL);
+}
+
+static const struct ptp_clock_info ptp_vclock_info = {
+	.owner		= THIS_MODULE,
+	.name		= "ptp virtual clock",
+	.max_adj	= 500000000,
+	.adjfine	= ptp_vclock_adjfine,
+	.adjtime	= ptp_vclock_adjtime,
+	.settime64	= ptp_vclock_settime,
+	.do_aux_work	= ptp_vclock_refresh,
+};
+
+static u64 ptp_vclock_read(struct cyclecounter *cc)
+{
+	struct ptp_vclock *vclock = cc_to_vclock(cc);
+	struct ptp_clock *ptp = vclock->pclock;
+	struct timespec64 ts = {};
+
+	ptp->info->getcycles64(ptp->info, &ts);
+
+	return timespec64_to_ns(&ts);
+}
+
+static const struct cyclecounter ptp_vclock_cc = {
+	.read	= ptp_vclock_read,
+	.mask	= CYCLECOUNTER_MASK(32),
+	.mult	= PTP_VCLOCK_CC_MULT,
+	.shift	= PTP_VCLOCK_CC_SHIFT,
+};
+
+struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock)
+{
+	struct ptp_vclock *vclock;
+
+	vclock = kzalloc_obj(*vclock);
+	if (!vclock)
+		return NULL;
+
+	vclock->pclock = pclock;
+	vclock->info = ptp_vclock_info;
+	if (pclock->info->getcyclesx64)
+		vclock->info.gettimex64 = ptp_vclock_gettimex;
+	else
+		vclock->info.gettime64 = ptp_vclock_gettime;
+	if (pclock->info->getcrosscycles)
+		vclock->info.getcrosststamp = ptp_vclock_getcrosststamp;
+	vclock->cc = ptp_vclock_cc;
+
+	snprintf(vclock->info.name, PTP_CLOCK_NAME_LEN, "ptp%d_virt",
+		 pclock->index);
+
+	INIT_HLIST_NODE(&vclock->vclock_hash_node);
+
+	mutex_init(&vclock->lock);
+
+	vclock->clock = ptp_clock_register(&vclock->info, &pclock->dev);
+	if (IS_ERR_OR_NULL(vclock->clock)) {
+		kfree(vclock);
+		return NULL;
+	}
+
+	ptp_vclock_set_subclass(vclock->clock);
+
+	timecounter_init(&vclock->tc, &vclock->cc, 0);
+	ptp_schedule_worker(vclock->clock, PTP_VCLOCK_REFRESH_INTERVAL);
+
+	ptp_vclock_hash_add(vclock);
+
+	return vclock;
+}
+
+void ptp_vclock_unregister(struct ptp_vclock *vclock)
+{
+	ptp_vclock_hash_del(vclock);
+
+	ptp_clock_unregister(vclock->clock);
+	kfree(vclock);
+}
+
+#if IS_BUILTIN(CONFIG_PTP_1588_CLOCK)
+int ptp_get_vclocks_index(int pclock_index, int **vclock_index)
+{
+	char name[PTP_CLOCK_NAME_LEN] = "";
+	struct ptp_clock *ptp;
+	struct device *dev;
+	int num = 0;
+
+	if (pclock_index < 0)
+		return num;
+
+	snprintf(name, PTP_CLOCK_NAME_LEN, "ptp%d", pclock_index);
+	dev = class_find_device_by_name(&ptp_class, name);
+	if (!dev)
+		return num;
+
+	ptp = dev_get_drvdata(dev);
+
+	if (mutex_lock_interruptible(&ptp->n_vclocks_mux)) {
+		put_device(dev);
+		return num;
+	}
+
+	*vclock_index = kzalloc(sizeof(int) * ptp->n_vclocks, GFP_KERNEL);
+	if (!(*vclock_index))
+		goto out;
+
+	memcpy(*vclock_index, ptp->vclock_index, sizeof(int) * ptp->n_vclocks);
+	num = ptp->n_vclocks;
+out:
+	mutex_unlock(&ptp->n_vclocks_mux);
+	put_device(dev);
+	return num;
+}
+EXPORT_SYMBOL(ptp_get_vclocks_index);
+
+ktime_t ptp_convert_timestamp(const ktime_t *hwtstamp, int vclock_index)
+{
+	unsigned int hash = vclock_index % HASH_SIZE(vclock_hash);
+	struct ptp_vclock *vclock;
+	u64 vclock_ns = 0;
+	int srcu_idx;
+	u64 ns;
+
+	ns = ktime_to_ns(*hwtstamp);
+
+	srcu_idx = srcu_read_lock(&vclock_srcu);
+
+	hlist_for_each_entry_srcu(vclock, &vclock_hash[hash], vclock_hash_node,
+				  srcu_read_lock_held(&vclock_srcu)) {
+		if (vclock->clock->index != vclock_index)
+			continue;
+
+		if (mutex_lock_interruptible(&vclock->lock))
+			break;
+		vclock_ns = timecounter_cyc2time(&vclock->tc, ns);
+		mutex_unlock(&vclock->lock);
+		break;
+	}
+
+	srcu_read_unlock(&vclock_srcu, srcu_idx);
+
+	return ns_to_ktime(vclock_ns);
+}
+EXPORT_SYMBOL(ptp_convert_timestamp);
+#endif