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, 295 insertions, 0 deletions

diff --git a/crypto/jitterentropy-testing.c b/crypto/jitterentropy-testing.c
new file mode 100644
index 000000000..21c9d7c32
--- /dev/null
+++ b/crypto/jitterentropy-testing.c
@@ -0,0 +1,295 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * Test interface for Jitter RNG.
+ *
+ * Copyright (C) 2023, Stephan Mueller <smueller@chronox.de>
+ */
+
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+
+#include "jitterentropy.h"
+
+#define JENT_TEST_RINGBUFFER_SIZE	(1<<10)
+#define JENT_TEST_RINGBUFFER_MASK	(JENT_TEST_RINGBUFFER_SIZE - 1)
+
+struct jent_testing {
+	u64 jent_testing_rb[JENT_TEST_RINGBUFFER_SIZE];
+	u32 rb_reader;
+	atomic_t rb_writer;
+	atomic_t jent_testing_enabled;
+	spinlock_t lock;
+	wait_queue_head_t read_wait;
+};
+
+static struct dentry *jent_raw_debugfs_root = NULL;
+
+/*************************** Generic Data Handling ****************************/
+
+/*
+ * boot variable:
+ * 0 ==> No boot test, gathering of runtime data allowed
+ * 1 ==> Boot test enabled and ready for collecting data, gathering runtime
+ *	 data is disabled
+ * 2 ==> Boot test completed and disabled, gathering of runtime data is
+ *	 disabled
+ */
+
+static void jent_testing_reset(struct jent_testing *data)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&data->lock, flags);
+	data->rb_reader = 0;
+	atomic_set(&data->rb_writer, 0);
+	spin_unlock_irqrestore(&data->lock, flags);
+}
+
+static void jent_testing_data_init(struct jent_testing *data, u32 boot)
+{
+	/*
+	 * The boot time testing implies we have a running test. If the
+	 * caller wants to clear it, he has to unset the boot_test flag
+	 * at runtime via sysfs to enable regular runtime testing
+	 */
+	if (boot)
+		return;
+
+	jent_testing_reset(data);
+	atomic_set(&data->jent_testing_enabled, 1);
+	pr_warn("Enabling data collection\n");
+}
+
+static void jent_testing_fini(struct jent_testing *data, u32 boot)
+{
+	/* If we have boot data, we do not reset yet to allow data to be read */
+	if (boot)
+		return;
+
+	atomic_set(&data->jent_testing_enabled, 0);
+	jent_testing_reset(data);
+	pr_warn("Disabling data collection\n");
+}
+
+static bool jent_testing_store(struct jent_testing *data, u64 value,
+			       u32 *boot)
+{
+	unsigned long flags;
+
+	if (!atomic_read(&data->jent_testing_enabled) && (*boot != 1))
+		return false;
+
+	spin_lock_irqsave(&data->lock, flags);
+
+	/*
+	 * Disable entropy testing for boot time testing after ring buffer
+	 * is filled.
+	 */
+	if (*boot) {
+		if (((u32)atomic_read(&data->rb_writer)) >
+		     JENT_TEST_RINGBUFFER_SIZE) {
+			*boot = 2;
+			pr_warn_once("One time data collection test disabled\n");
+			spin_unlock_irqrestore(&data->lock, flags);
+			return false;
+		}
+
+		if (atomic_read(&data->rb_writer) == 1)
+			pr_warn("One time data collection test enabled\n");
+	}
+
+	data->jent_testing_rb[((u32)atomic_read(&data->rb_writer)) &
+			      JENT_TEST_RINGBUFFER_MASK] = value;
+	atomic_inc(&data->rb_writer);
+
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	if (wq_has_sleeper(&data->read_wait))
+		wake_up_interruptible(&data->read_wait);
+
+	return true;
+}
+
+static bool jent_testing_have_data(struct jent_testing *data)
+{
+	return ((((u32)atomic_read(&data->rb_writer)) &
+		 JENT_TEST_RINGBUFFER_MASK) !=
+		 (data->rb_reader & JENT_TEST_RINGBUFFER_MASK));
+}
+
+static int jent_testing_reader(struct jent_testing *data, u32 *boot,
+			       u8 *outbuf, u32 outbuflen)
+{
+	unsigned long flags;
+	int collected_data = 0;
+
+	jent_testing_data_init(data, *boot);
+
+	while (outbuflen) {
+		u32 writer = (u32)atomic_read(&data->rb_writer);
+
+		spin_lock_irqsave(&data->lock, flags);
+
+		/* We have no data or reached the writer. */
+		if (!writer || (writer == data->rb_reader)) {
+
+			spin_unlock_irqrestore(&data->lock, flags);
+
+			/*
+			 * Now we gathered all boot data, enable regular data
+			 * collection.
+			 */
+			if (*boot) {
+				*boot = 0;
+				goto out;
+			}
+
+			wait_event_interruptible(data->read_wait,
+						 jent_testing_have_data(data));
+			if (signal_pending(current)) {
+				collected_data = -ERESTARTSYS;
+				goto out;
+			}
+
+			continue;
+		}
+
+		/* We copy out word-wise */
+		if (outbuflen < sizeof(u64)) {
+			spin_unlock_irqrestore(&data->lock, flags);
+			goto out;
+		}
+
+		memcpy(outbuf, &data->jent_testing_rb[data->rb_reader],
+		       sizeof(u64));
+		data->rb_reader++;
+
+		spin_unlock_irqrestore(&data->lock, flags);
+
+		outbuf += sizeof(u64);
+		outbuflen -= sizeof(u64);
+		collected_data += sizeof(u64);
+	}
+
+out:
+	jent_testing_fini(data, *boot);
+	return collected_data;
+}
+
+static int jent_testing_extract_user(struct file *file, char __user *buf,
+				     size_t nbytes, loff_t *ppos,
+				     int (*reader)(u8 *outbuf, u32 outbuflen))
+{
+	u8 *tmp, *tmp_aligned;
+	int ret = 0, large_request = (nbytes > 256);
+
+	if (!nbytes)
+		return 0;
+
+	/*
+	 * The intention of this interface is for collecting at least
+	 * 1000 samples due to the SP800-90B requirements. However, due to
+	 * memory and performance constraints, it is not desirable to allocate
+	 * 8000 bytes of memory. Instead, we allocate space for only 125
+	 * samples, which will allow the user to collect all 1000 samples using
+	 * 8 calls to this interface.
+	 */
+	tmp = kmalloc(125 * sizeof(u64) + sizeof(u64), GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	tmp_aligned = PTR_ALIGN(tmp, sizeof(u64));
+
+	while (nbytes) {
+		int i;
+
+		if (large_request && need_resched()) {
+			if (signal_pending(current)) {
+				if (ret == 0)
+					ret = -ERESTARTSYS;
+				break;
+			}
+			schedule();
+		}
+
+		i = min_t(int, nbytes, 125 * sizeof(u64));
+		i = reader(tmp_aligned, i);
+		if (i <= 0) {
+			if (i < 0)
+				ret = i;
+			break;
+		}
+		if (copy_to_user(buf, tmp_aligned, i)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		nbytes -= i;
+		buf += i;
+		ret += i;
+	}
+
+	kfree_sensitive(tmp);
+
+	if (ret > 0)
+		*ppos += ret;
+
+	return ret;
+}
+
+/************** Raw High-Resolution Timer Entropy Data Handling **************/
+
+static u32 boot_raw_hires_test = 0;
+module_param(boot_raw_hires_test, uint, 0644);
+MODULE_PARM_DESC(boot_raw_hires_test,
+		 "Enable gathering boot time high resolution timer entropy of the first Jitter RNG entropy events");
+
+static struct jent_testing jent_raw_hires = {
+	.rb_reader = 0,
+	.rb_writer = ATOMIC_INIT(0),
+	.lock      = __SPIN_LOCK_UNLOCKED(jent_raw_hires.lock),
+	.read_wait = __WAIT_QUEUE_HEAD_INITIALIZER(jent_raw_hires.read_wait)
+};
+
+int jent_raw_hires_entropy_store(__u64 value)
+{
+	return jent_testing_store(&jent_raw_hires, value, &boot_raw_hires_test);
+}
+EXPORT_SYMBOL(jent_raw_hires_entropy_store);
+
+static int jent_raw_hires_entropy_reader(u8 *outbuf, u32 outbuflen)
+{
+	return jent_testing_reader(&jent_raw_hires, &boot_raw_hires_test,
+				   outbuf, outbuflen);
+}
+
+static ssize_t jent_raw_hires_read(struct file *file, char __user *to,
+				   size_t count, loff_t *ppos)
+{
+	return jent_testing_extract_user(file, to, count, ppos,
+					 jent_raw_hires_entropy_reader);
+}
+
+static const struct file_operations jent_raw_hires_fops = {
+	.owner = THIS_MODULE,
+	.read = jent_raw_hires_read,
+};
+
+/******************************* Initialization *******************************/
+
+void jent_testing_init(void)
+{
+	jent_raw_debugfs_root = debugfs_create_dir(KBUILD_MODNAME, NULL);
+
+	debugfs_create_file_unsafe("jent_raw_hires", 0400,
+				   jent_raw_debugfs_root, NULL,
+				   &jent_raw_hires_fops);
+}
+EXPORT_SYMBOL(jent_testing_init);
+
+void jent_testing_exit(void)
+{
+	debugfs_remove_recursive(jent_raw_debugfs_root);
+}
+EXPORT_SYMBOL(jent_testing_exit);