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, 255 insertions, 0 deletions

diff --git a/drivers/media/rc/ir-rcmm-decoder.c b/drivers/media/rc/ir-rcmm-decoder.c
new file mode 100644
index 000000000..a8a34436f
--- /dev/null
+++ b/drivers/media/rc/ir-rcmm-decoder.c
@@ -0,0 +1,255 @@
+// SPDX-License-Identifier: GPL-2.0+
+// ir-rcmm-decoder.c - A decoder for the RCMM IR protocol
+//
+// Copyright (C) 2018 by Patrick Lerda <patrick9876@free.fr>
+
+#include "rc-core-priv.h"
+#include <linux/module.h>
+
+#define RCMM_UNIT		166  /* microseconds */
+#define RCMM_PREFIX_PULSE	417  /* 166.666666666666*2.5 */
+#define RCMM_PULSE_0            278  /* 166.666666666666*(1+2/3) */
+#define RCMM_PULSE_1            444  /* 166.666666666666*(2+2/3) */
+#define RCMM_PULSE_2            611  /* 166.666666666666*(3+2/3) */
+#define RCMM_PULSE_3            778  /* 166.666666666666*(4+2/3) */
+
+enum rcmm_state {
+	STATE_INACTIVE,
+	STATE_LOW,
+	STATE_BUMP,
+	STATE_VALUE,
+	STATE_FINISHED,
+};
+
+static bool rcmm_mode(const struct rcmm_dec *data)
+{
+	return !((0x000c0000 & data->bits) == 0x000c0000);
+}
+
+static int rcmm_miscmode(struct rc_dev *dev, struct rcmm_dec *data)
+{
+	switch (data->count) {
+	case 24:
+		if (dev->enabled_protocols & RC_PROTO_BIT_RCMM24) {
+			rc_keydown(dev, RC_PROTO_RCMM24, data->bits, 0);
+			data->state = STATE_INACTIVE;
+			return 0;
+		}
+		return -1;
+
+	case 12:
+		if (dev->enabled_protocols & RC_PROTO_BIT_RCMM12) {
+			rc_keydown(dev, RC_PROTO_RCMM12, data->bits, 0);
+			data->state = STATE_INACTIVE;
+			return 0;
+		}
+		return -1;
+	}
+
+	return -1;
+}
+
+/**
+ * ir_rcmm_decode() - Decode one RCMM 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_rcmm_decode(struct rc_dev *dev, struct ir_raw_event ev)
+{
+	struct rcmm_dec *data = &dev->raw->rcmm;
+	u32 scancode;
+	u8 toggle;
+	int value;
+
+	if (!(dev->enabled_protocols & (RC_PROTO_BIT_RCMM32 |
+					RC_PROTO_BIT_RCMM24 |
+					RC_PROTO_BIT_RCMM12)))
+		return 0;
+
+	if (!is_timing_event(ev)) {
+		if (ev.overflow)
+			data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	switch (data->state) {
+	case STATE_INACTIVE:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, RCMM_PREFIX_PULSE, RCMM_UNIT))
+			break;
+
+		data->state = STATE_LOW;
+		data->count = 0;
+		data->bits  = 0;
+		return 0;
+
+	case STATE_LOW:
+		if (ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, RCMM_PULSE_0, RCMM_UNIT))
+			break;
+
+		data->state = STATE_BUMP;
+		return 0;
+
+	case STATE_BUMP:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, RCMM_UNIT, RCMM_UNIT / 2))
+			break;
+
+		data->state = STATE_VALUE;
+		return 0;
+
+	case STATE_VALUE:
+		if (ev.pulse)
+			break;
+
+		if (eq_margin(ev.duration, RCMM_PULSE_0, RCMM_UNIT / 2))
+			value = 0;
+		else if (eq_margin(ev.duration, RCMM_PULSE_1, RCMM_UNIT / 2))
+			value = 1;
+		else if (eq_margin(ev.duration, RCMM_PULSE_2, RCMM_UNIT / 2))
+			value = 2;
+		else if (eq_margin(ev.duration, RCMM_PULSE_3, RCMM_UNIT / 2))
+			value = 3;
+		else
+			value = -1;
+
+		if (value == -1) {
+			if (!rcmm_miscmode(dev, data))
+				return 0;
+			break;
+		}
+
+		data->bits <<= 2;
+		data->bits |= value;
+
+		data->count += 2;
+
+		if (data->count < 32)
+			data->state = STATE_BUMP;
+		else
+			data->state = STATE_FINISHED;
+
+		return 0;
+
+	case STATE_FINISHED:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, RCMM_UNIT, RCMM_UNIT / 2))
+			break;
+
+		if (rcmm_mode(data)) {
+			toggle = !!(0x8000 & data->bits);
+			scancode = data->bits & ~0x8000;
+		} else {
+			toggle = 0;
+			scancode = data->bits;
+		}
+
+		if (dev->enabled_protocols & RC_PROTO_BIT_RCMM32) {
+			rc_keydown(dev, RC_PROTO_RCMM32, scancode, toggle);
+			data->state = STATE_INACTIVE;
+			return 0;
+		}
+
+		break;
+	}
+
+	dev_dbg(&dev->dev, "RC-MM 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 int rcmmspace[] = {
+	RCMM_PULSE_0,
+	RCMM_PULSE_1,
+	RCMM_PULSE_2,
+	RCMM_PULSE_3,
+};
+
+static int ir_rcmm_rawencoder(struct ir_raw_event **ev, unsigned int max,
+			      unsigned int n, u32 data)
+{
+	int i;
+	int ret;
+
+	ret = ir_raw_gen_pulse_space(ev, &max, RCMM_PREFIX_PULSE, RCMM_PULSE_0);
+	if (ret)
+		return ret;
+
+	for (i = n - 2; i >= 0; i -= 2) {
+		const unsigned int space = rcmmspace[(data >> i) & 3];
+
+		ret = ir_raw_gen_pulse_space(ev, &max, RCMM_UNIT, space);
+		if (ret)
+			return ret;
+	}
+
+	return ir_raw_gen_pulse_space(ev, &max, RCMM_UNIT, RCMM_PULSE_3 * 2);
+}
+
+static int ir_rcmm_encode(enum rc_proto protocol, u32 scancode,
+			  struct ir_raw_event *events, unsigned int max)
+{
+	struct ir_raw_event *e = events;
+	int ret;
+
+	switch (protocol) {
+	case RC_PROTO_RCMM32:
+		ret = ir_rcmm_rawencoder(&e, max, 32, scancode);
+		break;
+	case RC_PROTO_RCMM24:
+		ret = ir_rcmm_rawencoder(&e, max, 24, scancode);
+		break;
+	case RC_PROTO_RCMM12:
+		ret = ir_rcmm_rawencoder(&e, max, 12, scancode);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret < 0)
+		return ret;
+
+	return e - events;
+}
+
+static struct ir_raw_handler rcmm_handler = {
+	.protocols	= RC_PROTO_BIT_RCMM32 |
+			  RC_PROTO_BIT_RCMM24 |
+			  RC_PROTO_BIT_RCMM12,
+	.decode		= ir_rcmm_decode,
+	.encode         = ir_rcmm_encode,
+	.carrier        = 36000,
+	.min_timeout	= RCMM_PULSE_3 + RCMM_UNIT,
+};
+
+static int __init ir_rcmm_decode_init(void)
+{
+	ir_raw_handler_register(&rcmm_handler);
+
+	pr_info("IR RCMM protocol handler initialized\n");
+	return 0;
+}
+
+static void __exit ir_rcmm_decode_exit(void)
+{
+	ir_raw_handler_unregister(&rcmm_handler);
+}
+
+module_init(ir_rcmm_decode_init);
+module_exit(ir_rcmm_decode_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Patrick Lerda");
+MODULE_DESCRIPTION("RCMM IR protocol decoder");