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, 296 insertions, 0 deletions

diff --git a/drivers/media/rc/ir-rc5-decoder.c b/drivers/media/rc/ir-rc5-decoder.c
new file mode 100644
index 000000000..82d7f6ad2
--- /dev/null
+++ b/drivers/media/rc/ir-rc5-decoder.c
@@ -0,0 +1,296 @@
+// SPDX-License-Identifier: GPL-2.0
+// ir-rc5-decoder.c - decoder for RC5(x) and StreamZap protocols
+//
+// Copyright (C) 2010 by Mauro Carvalho Chehab
+// Copyright (C) 2010 by Jarod Wilson <jarod@redhat.com>
+
+/*
+ * This decoder handles the 14 bit RC5 protocol, 15 bit "StreamZap" protocol
+ * and 20 bit RC5x protocol.
+ */
+
+#include "rc-core-priv.h"
+#include <linux/module.h>
+
+#define RC5_NBITS		14
+#define RC5_SZ_NBITS		15
+#define RC5X_NBITS		20
+#define CHECK_RC5X_NBITS	8
+#define RC5_UNIT		889 /* us */
+#define RC5_BIT_START		(1 * RC5_UNIT)
+#define RC5_BIT_END		(1 * RC5_UNIT)
+#define RC5X_SPACE		(4 * RC5_UNIT)
+#define RC5_TRAILER		(6 * RC5_UNIT) /* In reality, approx 100 */
+
+enum rc5_state {
+	STATE_INACTIVE,
+	STATE_BIT_START,
+	STATE_BIT_END,
+	STATE_CHECK_RC5X,
+	STATE_FINISHED,
+};
+
+/**
+ * ir_rc5_decode() - Decode one RC-5 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_rc5_decode(struct rc_dev *dev, struct ir_raw_event ev)
+{
+	struct rc5_dec *data = &dev->raw->rc5;
+	u8 toggle;
+	u32 scancode;
+	enum rc_proto protocol;
+
+	if (!is_timing_event(ev)) {
+		if (ev.overflow)
+			data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	if (!geq_margin(ev.duration, RC5_UNIT, RC5_UNIT / 2))
+		goto out;
+
+again:
+	dev_dbg(&dev->dev, "RC5(x/sz) decode started at state %i (%uus %s)\n",
+		data->state, ev.duration, TO_STR(ev.pulse));
+
+	if (!geq_margin(ev.duration, RC5_UNIT, RC5_UNIT / 2))
+		return 0;
+
+	switch (data->state) {
+
+	case STATE_INACTIVE:
+		if (!ev.pulse)
+			break;
+
+		data->state = STATE_BIT_START;
+		data->count = 1;
+		decrease_duration(&ev, RC5_BIT_START);
+		goto again;
+
+	case STATE_BIT_START:
+		if (!ev.pulse && geq_margin(ev.duration, RC5_TRAILER, RC5_UNIT / 2)) {
+			data->state = STATE_FINISHED;
+			goto again;
+		}
+
+		if (!eq_margin(ev.duration, RC5_BIT_START, RC5_UNIT / 2))
+			break;
+
+		data->bits <<= 1;
+		if (!ev.pulse)
+			data->bits |= 1;
+		data->count++;
+		data->state = STATE_BIT_END;
+		return 0;
+
+	case STATE_BIT_END:
+		if (data->count == CHECK_RC5X_NBITS)
+			data->state = STATE_CHECK_RC5X;
+		else
+			data->state = STATE_BIT_START;
+
+		decrease_duration(&ev, RC5_BIT_END);
+		goto again;
+
+	case STATE_CHECK_RC5X:
+		if (!ev.pulse && geq_margin(ev.duration, RC5X_SPACE, RC5_UNIT / 2)) {
+			data->is_rc5x = true;
+			decrease_duration(&ev, RC5X_SPACE);
+		} else
+			data->is_rc5x = false;
+		data->state = STATE_BIT_START;
+		goto again;
+
+	case STATE_FINISHED:
+		if (ev.pulse)
+			break;
+
+		if (data->is_rc5x && data->count == RC5X_NBITS) {
+			/* RC5X */
+			u8 xdata, command, system;
+			if (!(dev->enabled_protocols & RC_PROTO_BIT_RC5X_20)) {
+				data->state = STATE_INACTIVE;
+				return 0;
+			}
+			xdata    = (data->bits & 0x0003F) >> 0;
+			command  = (data->bits & 0x00FC0) >> 6;
+			system   = (data->bits & 0x1F000) >> 12;
+			toggle   = (data->bits & 0x20000) ? 1 : 0;
+			command += (data->bits & 0x40000) ? 0 : 0x40;
+			scancode = system << 16 | command << 8 | xdata;
+			protocol = RC_PROTO_RC5X_20;
+
+		} else if (!data->is_rc5x && data->count == RC5_NBITS) {
+			/* RC5 */
+			u8 command, system;
+			if (!(dev->enabled_protocols & RC_PROTO_BIT_RC5)) {
+				data->state = STATE_INACTIVE;
+				return 0;
+			}
+			command  = (data->bits & 0x0003F) >> 0;
+			system   = (data->bits & 0x007C0) >> 6;
+			toggle   = (data->bits & 0x00800) ? 1 : 0;
+			command += (data->bits & 0x01000) ? 0 : 0x40;
+			scancode = system << 8 | command;
+			protocol = RC_PROTO_RC5;
+
+		} else if (!data->is_rc5x && data->count == RC5_SZ_NBITS) {
+			/* RC5 StreamZap */
+			u8 command, system;
+			if (!(dev->enabled_protocols & RC_PROTO_BIT_RC5_SZ)) {
+				data->state = STATE_INACTIVE;
+				return 0;
+			}
+			command  = (data->bits & 0x0003F) >> 0;
+			system   = (data->bits & 0x02FC0) >> 6;
+			toggle   = (data->bits & 0x01000) ? 1 : 0;
+			scancode = system << 6 | command;
+			protocol = RC_PROTO_RC5_SZ;
+
+		} else
+			break;
+
+		dev_dbg(&dev->dev, "RC5(x/sz) scancode 0x%06x (p: %u, t: %u)\n",
+			scancode, protocol, toggle);
+
+		rc_keydown(dev, protocol, scancode, toggle);
+		data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+out:
+	dev_dbg(&dev->dev, "RC5(x/sz) decode failed at state %i count %d (%uus %s)\n",
+		data->state, data->count, ev.duration, TO_STR(ev.pulse));
+	data->state = STATE_INACTIVE;
+	return -EINVAL;
+}
+
+static const struct ir_raw_timings_manchester ir_rc5_timings = {
+	.leader_pulse		= RC5_UNIT,
+	.clock			= RC5_UNIT,
+	.trailer_space		= RC5_UNIT * 10,
+};
+
+static const struct ir_raw_timings_manchester ir_rc5x_timings[2] = {
+	{
+		.leader_pulse		= RC5_UNIT,
+		.clock			= RC5_UNIT,
+		.trailer_space		= RC5X_SPACE,
+	},
+	{
+		.clock			= RC5_UNIT,
+		.trailer_space		= RC5_UNIT * 10,
+	},
+};
+
+static const struct ir_raw_timings_manchester ir_rc5_sz_timings = {
+	.leader_pulse			= RC5_UNIT,
+	.clock				= RC5_UNIT,
+	.trailer_space			= RC5_UNIT * 10,
+};
+
+/**
+ * ir_rc5_encode() - Encode a scancode as a stream of raw events
+ *
+ * @protocol:	protocol variant 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.
+ *		-EINVAL if the scancode is ambiguous or invalid.
+ */
+static int ir_rc5_encode(enum rc_proto protocol, u32 scancode,
+			 struct ir_raw_event *events, unsigned int max)
+{
+	int ret;
+	struct ir_raw_event *e = events;
+	unsigned int data, xdata, command, commandx, system, pre_space_data;
+
+	/* Detect protocol and convert scancode to raw data */
+	if (protocol == RC_PROTO_RC5) {
+		/* decode scancode */
+		command  = (scancode & 0x003f) >> 0;
+		commandx = (scancode & 0x0040) >> 6;
+		system   = (scancode & 0x1f00) >> 8;
+		/* encode data */
+		data = !commandx << 12 | system << 6 | command;
+
+		/* First bit is encoded by leader_pulse */
+		ret = ir_raw_gen_manchester(&e, max, &ir_rc5_timings,
+					    RC5_NBITS - 1, data);
+		if (ret < 0)
+			return ret;
+	} else if (protocol == RC_PROTO_RC5X_20) {
+		/* decode scancode */
+		xdata    = (scancode & 0x00003f) >> 0;
+		command  = (scancode & 0x003f00) >> 8;
+		commandx = !(scancode & 0x004000);
+		system   = (scancode & 0x1f0000) >> 16;
+
+		/* encode data */
+		data = commandx << 18 | system << 12 | command << 6 | xdata;
+
+		/* First bit is encoded by leader_pulse */
+		pre_space_data = data >> (RC5X_NBITS - CHECK_RC5X_NBITS);
+		ret = ir_raw_gen_manchester(&e, max, &ir_rc5x_timings[0],
+					    CHECK_RC5X_NBITS - 1,
+					    pre_space_data);
+		if (ret < 0)
+			return ret;
+		ret = ir_raw_gen_manchester(&e, max - (e - events),
+					    &ir_rc5x_timings[1],
+					    RC5X_NBITS - CHECK_RC5X_NBITS,
+					    data);
+		if (ret < 0)
+			return ret;
+	} else if (protocol == RC_PROTO_RC5_SZ) {
+		/* RC5-SZ scancode is raw enough for Manchester as it is */
+		/* First bit is encoded by leader_pulse */
+		ret = ir_raw_gen_manchester(&e, max, &ir_rc5_sz_timings,
+					    RC5_SZ_NBITS - 1,
+					    scancode & 0x2fff);
+		if (ret < 0)
+			return ret;
+	} else {
+		return -EINVAL;
+	}
+
+	return e - events;
+}
+
+static struct ir_raw_handler rc5_handler = {
+	.protocols	= RC_PROTO_BIT_RC5 | RC_PROTO_BIT_RC5X_20 |
+							RC_PROTO_BIT_RC5_SZ,
+	.decode		= ir_rc5_decode,
+	.encode		= ir_rc5_encode,
+	.carrier	= 36000,
+	.min_timeout	= RC5_TRAILER,
+};
+
+static int __init ir_rc5_decode_init(void)
+{
+	ir_raw_handler_register(&rc5_handler);
+
+	printk(KERN_INFO "IR RC5(x/sz) protocol handler initialized\n");
+	return 0;
+}
+
+static void __exit ir_rc5_decode_exit(void)
+{
+	ir_raw_handler_unregister(&rc5_handler);
+}
+
+module_init(ir_rc5_decode_init);
+module_exit(ir_rc5_decode_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Mauro Carvalho Chehab and Jarod Wilson");
+MODULE_AUTHOR("Red Hat Inc. (http://www.redhat.com)");
+MODULE_DESCRIPTION("RC5(x/sz) IR protocol decoder");