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, 217 insertions, 0 deletions

diff --git a/drivers/media/rc/ir-xmp-decoder.c b/drivers/media/rc/ir-xmp-decoder.c
new file mode 100644
index 000000000..dc36b6873
--- /dev/null
+++ b/drivers/media/rc/ir-xmp-decoder.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* ir-xmp-decoder.c - handle XMP IR Pulse/Space protocol
+ *
+ * Copyright (C) 2014 by Marcel Mol
+ *
+ * - Based on info from http://www.hifi-remote.com
+ * - Ignore Toggle=9 frames
+ * - Ignore XMP-1 XMP-2 difference, always store 16 bit OBC
+ */
+
+#include <linux/bitrev.h>
+#include <linux/module.h>
+#include "rc-core-priv.h"
+
+#define XMP_UNIT		  136 /* us */
+#define XMP_LEADER		  210 /* us */
+#define XMP_NIBBLE_PREFIX	  760 /* us */
+#define	XMP_HALFFRAME_SPACE	13800 /* us */
+/* should be 80ms but not all duration supliers can go that high */
+#define	XMP_TRAILER_SPACE	20000
+
+enum xmp_state {
+	STATE_INACTIVE,
+	STATE_LEADER_PULSE,
+	STATE_NIBBLE_SPACE,
+};
+
+/**
+ * ir_xmp_decode() - Decode one XMP pulse or space
+ * @dev:	the struct rc_dev descriptor of the device
+ * @ev:		the struct ir_raw_event descriptor of the pulse/space
+ *
+ * This function returns -EINVAL if the pulse violates the state machine
+ */
+static int ir_xmp_decode(struct rc_dev *dev, struct ir_raw_event ev)
+{
+	struct xmp_dec *data = &dev->raw->xmp;
+
+	if (!is_timing_event(ev)) {
+		if (ev.overflow)
+			data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	dev_dbg(&dev->dev, "XMP decode started at state %d %d (%uus %s)\n",
+		data->state, data->count, ev.duration, TO_STR(ev.pulse));
+
+	switch (data->state) {
+
+	case STATE_INACTIVE:
+		if (!ev.pulse)
+			break;
+
+		if (eq_margin(ev.duration, XMP_LEADER, XMP_UNIT / 2)) {
+			data->count = 0;
+			data->state = STATE_NIBBLE_SPACE;
+		}
+
+		return 0;
+
+	case STATE_LEADER_PULSE:
+		if (!ev.pulse)
+			break;
+
+		if (eq_margin(ev.duration, XMP_LEADER, XMP_UNIT / 2))
+			data->state = STATE_NIBBLE_SPACE;
+
+		return 0;
+
+	case STATE_NIBBLE_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (geq_margin(ev.duration, XMP_TRAILER_SPACE, XMP_NIBBLE_PREFIX)) {
+			int divider, i;
+			u8 addr, subaddr, subaddr2, toggle, oem, obc1, obc2, sum1, sum2;
+			u32 *n;
+			u32 scancode;
+
+			if (data->count != 16) {
+				dev_dbg(&dev->dev, "received TRAILER period at index %d: %u\n",
+					data->count, ev.duration);
+				data->state = STATE_INACTIVE;
+				return -EINVAL;
+			}
+
+			n = data->durations;
+			/*
+			 * the 4th nibble should be 15 so base the divider on this
+			 * to transform durations into nibbles. Subtract 2000 from
+			 * the divider to compensate for fluctuations in the signal
+			 */
+			divider = (n[3] - XMP_NIBBLE_PREFIX) / 15 - 2000;
+			if (divider < 50) {
+				dev_dbg(&dev->dev, "divider to small %d.\n",
+					divider);
+				data->state = STATE_INACTIVE;
+				return -EINVAL;
+			}
+
+			/* convert to nibbles and do some sanity checks */
+			for (i = 0; i < 16; i++)
+				n[i] = (n[i] - XMP_NIBBLE_PREFIX) / divider;
+			sum1 = (15 + n[0] + n[1] + n[2] + n[3] +
+				n[4] + n[5] + n[6] + n[7]) % 16;
+			sum2 = (15 + n[8] + n[9] + n[10] + n[11] +
+				n[12] + n[13] + n[14] + n[15]) % 16;
+
+			if (sum1 != 15 || sum2 != 15) {
+				dev_dbg(&dev->dev, "checksum errors sum1=0x%X sum2=0x%X\n",
+					sum1, sum2);
+				data->state = STATE_INACTIVE;
+				return -EINVAL;
+			}
+
+			subaddr  = n[0] << 4 | n[2];
+			subaddr2 = n[8] << 4 | n[11];
+			oem      = n[4] << 4 | n[5];
+			addr     = n[6] << 4 | n[7];
+			toggle   = n[10];
+			obc1 = n[12] << 4 | n[13];
+			obc2 = n[14] << 4 | n[15];
+			if (subaddr != subaddr2) {
+				dev_dbg(&dev->dev, "subaddress nibbles mismatch 0x%02X != 0x%02X\n",
+					subaddr, subaddr2);
+				data->state = STATE_INACTIVE;
+				return -EINVAL;
+			}
+			if (oem != 0x44)
+				dev_dbg(&dev->dev, "Warning: OEM nibbles 0x%02X. Expected 0x44\n",
+					oem);
+
+			scancode = addr << 24 | subaddr << 16 |
+				   obc1 << 8 | obc2;
+			dev_dbg(&dev->dev, "XMP scancode 0x%06x\n", scancode);
+
+			if (toggle == 0) {
+				rc_keydown(dev, RC_PROTO_XMP, scancode, 0);
+			} else {
+				rc_repeat(dev);
+				dev_dbg(&dev->dev, "Repeat last key\n");
+			}
+			data->state = STATE_INACTIVE;
+
+			return 0;
+
+		} else if (geq_margin(ev.duration, XMP_HALFFRAME_SPACE, XMP_NIBBLE_PREFIX)) {
+			/* Expect 8 or 16 nibble pulses. 16 in case of 'final' frame */
+			if (data->count == 16) {
+				dev_dbg(&dev->dev, "received half frame pulse at index %d. Probably a final frame key-up event: %u\n",
+					data->count, ev.duration);
+				/*
+				 * TODO: for now go back to half frame position
+				 *	 so trailer can be found and key press
+				 *	 can be handled.
+				 */
+				data->count = 8;
+			}
+
+			else if (data->count != 8)
+				dev_dbg(&dev->dev, "received half frame pulse at index %d: %u\n",
+					data->count, ev.duration);
+			data->state = STATE_LEADER_PULSE;
+
+			return 0;
+
+		} else if (geq_margin(ev.duration, XMP_NIBBLE_PREFIX, XMP_UNIT)) {
+			/* store nibble raw data, decode after trailer */
+			if (data->count == 16) {
+				dev_dbg(&dev->dev, "too many pulses (%d) ignoring: %u\n",
+					data->count, ev.duration);
+				data->state = STATE_INACTIVE;
+				return -EINVAL;
+			}
+			data->durations[data->count] = ev.duration;
+			data->count++;
+			data->state = STATE_LEADER_PULSE;
+
+			return 0;
+
+		}
+
+		break;
+	}
+
+	dev_dbg(&dev->dev, "XMP decode failed at count %d state %d (%uus %s)\n",
+		data->count, data->state, ev.duration, TO_STR(ev.pulse));
+	data->state = STATE_INACTIVE;
+	return -EINVAL;
+}
+
+static struct ir_raw_handler xmp_handler = {
+	.protocols	= RC_PROTO_BIT_XMP,
+	.decode		= ir_xmp_decode,
+	.min_timeout	= XMP_TRAILER_SPACE,
+};
+
+static int __init ir_xmp_decode_init(void)
+{
+	ir_raw_handler_register(&xmp_handler);
+
+	printk(KERN_INFO "IR XMP protocol handler initialized\n");
+	return 0;
+}
+
+static void __exit ir_xmp_decode_exit(void)
+{
+	ir_raw_handler_unregister(&xmp_handler);
+}
+
+module_init(ir_xmp_decode_init);
+module_exit(ir_xmp_decode_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Marcel Mol <marcel@mesa.nl>");
+MODULE_AUTHOR("MESA Consulting (http://www.mesa.nl)");
+MODULE_DESCRIPTION("XMP IR protocol decoder");