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, 244 insertions, 0 deletions

diff --git a/drivers/media/rc/ir-sharp-decoder.c b/drivers/media/rc/ir-sharp-decoder.c
new file mode 100644
index 000000000..3311099cb
--- /dev/null
+++ b/drivers/media/rc/ir-sharp-decoder.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* ir-sharp-decoder.c - handle Sharp IR Pulse/Space protocol
+ *
+ * Copyright (C) 2013-2014 Imagination Technologies Ltd.
+ *
+ * Based on NEC decoder:
+ * Copyright (C) 2010 by Mauro Carvalho Chehab
+ */
+
+#include <linux/bitrev.h>
+#include <linux/module.h>
+#include "rc-core-priv.h"
+
+#define SHARP_NBITS		15
+#define SHARP_UNIT		40  /* us */
+#define SHARP_BIT_PULSE		(8    * SHARP_UNIT) /* 320us */
+#define SHARP_BIT_0_PERIOD	(25   * SHARP_UNIT) /* 1ms (680us space) */
+#define SHARP_BIT_1_PERIOD	(50   * SHARP_UNIT) /* 2ms (1680us space) */
+#define SHARP_BIT_0_SPACE	(17   * SHARP_UNIT) /* 680us space */
+#define SHARP_BIT_1_SPACE	(42   * SHARP_UNIT) /* 1680us space */
+#define SHARP_ECHO_SPACE	(1000 * SHARP_UNIT) /* 40 ms */
+#define SHARP_TRAILER_SPACE	(125  * SHARP_UNIT) /* 5 ms (even longer) */
+
+enum sharp_state {
+	STATE_INACTIVE,
+	STATE_BIT_PULSE,
+	STATE_BIT_SPACE,
+	STATE_TRAILER_PULSE,
+	STATE_ECHO_SPACE,
+	STATE_TRAILER_SPACE,
+};
+
+/**
+ * ir_sharp_decode() - Decode one Sharp 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_sharp_decode(struct rc_dev *dev, struct ir_raw_event ev)
+{
+	struct sharp_dec *data = &dev->raw->sharp;
+	u32 msg, echo, address, command, scancode;
+
+	if (!is_timing_event(ev)) {
+		if (ev.overflow)
+			data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	dev_dbg(&dev->dev, "Sharp decode started at state %d (%uus %s)\n",
+		data->state, ev.duration, TO_STR(ev.pulse));
+
+	switch (data->state) {
+
+	case STATE_INACTIVE:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, SHARP_BIT_PULSE,
+			       SHARP_BIT_PULSE / 2))
+			break;
+
+		data->count = 0;
+		data->pulse_len = ev.duration;
+		data->state = STATE_BIT_SPACE;
+		return 0;
+
+	case STATE_BIT_PULSE:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, SHARP_BIT_PULSE,
+			       SHARP_BIT_PULSE / 2))
+			break;
+
+		data->pulse_len = ev.duration;
+		data->state = STATE_BIT_SPACE;
+		return 0;
+
+	case STATE_BIT_SPACE:
+		if (ev.pulse)
+			break;
+
+		data->bits <<= 1;
+		if (eq_margin(data->pulse_len + ev.duration, SHARP_BIT_1_PERIOD,
+			      SHARP_BIT_PULSE * 2))
+			data->bits |= 1;
+		else if (!eq_margin(data->pulse_len + ev.duration,
+				    SHARP_BIT_0_PERIOD, SHARP_BIT_PULSE * 2))
+			break;
+		data->count++;
+
+		if (data->count == SHARP_NBITS ||
+		    data->count == SHARP_NBITS * 2)
+			data->state = STATE_TRAILER_PULSE;
+		else
+			data->state = STATE_BIT_PULSE;
+
+		return 0;
+
+	case STATE_TRAILER_PULSE:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, SHARP_BIT_PULSE,
+			       SHARP_BIT_PULSE / 2))
+			break;
+
+		if (data->count == SHARP_NBITS) {
+			/* exp,chk bits should be 1,0 */
+			if ((data->bits & 0x3) != 0x2 &&
+			/* DENON variant, both chk bits 0 */
+			    (data->bits & 0x3) != 0x0)
+				break;
+			data->state = STATE_ECHO_SPACE;
+		} else {
+			data->state = STATE_TRAILER_SPACE;
+		}
+		return 0;
+
+	case STATE_ECHO_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, SHARP_ECHO_SPACE,
+			       SHARP_ECHO_SPACE / 4))
+			break;
+
+		data->state = STATE_BIT_PULSE;
+
+		return 0;
+
+	case STATE_TRAILER_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (!geq_margin(ev.duration, SHARP_TRAILER_SPACE,
+				SHARP_BIT_PULSE / 2))
+			break;
+
+		/* Validate - command, ext, chk should be inverted in 2nd */
+		msg = (data->bits >> 15) & 0x7fff;
+		echo = data->bits & 0x7fff;
+		if ((msg ^ echo) != 0x3ff) {
+			dev_dbg(&dev->dev,
+				"Sharp checksum error: received 0x%04x, 0x%04x\n",
+				msg, echo);
+			break;
+		}
+
+		address = bitrev8((msg >> 7) & 0xf8);
+		command = bitrev8((msg >> 2) & 0xff);
+
+		scancode = address << 8 | command;
+		dev_dbg(&dev->dev, "Sharp scancode 0x%04x\n", scancode);
+
+		rc_keydown(dev, RC_PROTO_SHARP, scancode, 0);
+		data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	dev_dbg(&dev->dev, "Sharp 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 const struct ir_raw_timings_pd ir_sharp_timings = {
+	.header_pulse  = 0,
+	.header_space  = 0,
+	.bit_pulse     = SHARP_BIT_PULSE,
+	.bit_space[0]  = SHARP_BIT_0_SPACE,
+	.bit_space[1]  = SHARP_BIT_1_SPACE,
+	.trailer_pulse = SHARP_BIT_PULSE,
+	.trailer_space = SHARP_ECHO_SPACE,
+	.msb_first     = 1,
+};
+
+/**
+ * ir_sharp_encode() - Encode a scancode as a stream of raw events
+ *
+ * @protocol:	protocol to encode
+ * @scancode:	scancode to encode
+ * @events:	array of raw ir events to write into
+ * @max:	maximum size of @events
+ *
+ * Returns:	The number of events written.
+ *		-ENOBUFS if there isn't enough space in the array to fit the
+ *		encoding. In this case all @max events will have been written.
+ */
+static int ir_sharp_encode(enum rc_proto protocol, u32 scancode,
+			   struct ir_raw_event *events, unsigned int max)
+{
+	struct ir_raw_event *e = events;
+	int ret;
+	u32 raw;
+
+	raw = (((bitrev8(scancode >> 8) >> 3) << 8) & 0x1f00) |
+		bitrev8(scancode);
+	ret = ir_raw_gen_pd(&e, max, &ir_sharp_timings, SHARP_NBITS,
+			    (raw << 2) | 2);
+	if (ret < 0)
+		return ret;
+
+	max -= ret;
+
+	raw = (((bitrev8(scancode >> 8) >> 3) << 8) & 0x1f00) |
+		bitrev8(~scancode);
+	ret = ir_raw_gen_pd(&e, max, &ir_sharp_timings, SHARP_NBITS,
+			    (raw << 2) | 1);
+	if (ret < 0)
+		return ret;
+
+	return e - events;
+}
+
+static struct ir_raw_handler sharp_handler = {
+	.protocols	= RC_PROTO_BIT_SHARP,
+	.decode		= ir_sharp_decode,
+	.encode		= ir_sharp_encode,
+	.carrier	= 38000,
+	.min_timeout	= SHARP_ECHO_SPACE + SHARP_ECHO_SPACE / 4,
+};
+
+static int __init ir_sharp_decode_init(void)
+{
+	ir_raw_handler_register(&sharp_handler);
+
+	pr_info("IR Sharp protocol handler initialized\n");
+	return 0;
+}
+
+static void __exit ir_sharp_decode_exit(void)
+{
+	ir_raw_handler_unregister(&sharp_handler);
+}
+
+module_init(ir_sharp_decode_init);
+module_exit(ir_sharp_decode_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("James Hogan <jhogan@kernel.org>");
+MODULE_DESCRIPTION("Sharp IR protocol decoder");