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, 278 insertions, 0 deletions

diff --git a/drivers/media/rc/ir-nec-decoder.c b/drivers/media/rc/ir-nec-decoder.c
new file mode 100644
index 000000000..37b99432a
--- /dev/null
+++ b/drivers/media/rc/ir-nec-decoder.c
@@ -0,0 +1,278 @@
+// SPDX-License-Identifier: GPL-2.0
+// ir-nec-decoder.c - handle NEC IR Pulse/Space protocol
+//
+// Copyright (C) 2010 by Mauro Carvalho Chehab
+
+#include <linux/bitrev.h>
+#include <linux/module.h>
+#include "rc-core-priv.h"
+
+#define NEC_NBITS		32
+#define NEC_UNIT		563  /* us */
+#define NEC_HEADER_PULSE	(16 * NEC_UNIT)
+#define NECX_HEADER_PULSE	(8  * NEC_UNIT) /* Less common NEC variant */
+#define NEC_HEADER_SPACE	(8  * NEC_UNIT)
+#define NEC_REPEAT_SPACE	(4  * NEC_UNIT)
+#define NEC_BIT_PULSE		(1  * NEC_UNIT)
+#define NEC_BIT_0_SPACE		(1  * NEC_UNIT)
+#define NEC_BIT_1_SPACE		(3  * NEC_UNIT)
+#define	NEC_TRAILER_PULSE	(1  * NEC_UNIT)
+#define	NEC_TRAILER_SPACE	(10 * NEC_UNIT) /* even longer in reality */
+#define NECX_REPEAT_BITS	1
+
+enum nec_state {
+	STATE_INACTIVE,
+	STATE_HEADER_SPACE,
+	STATE_BIT_PULSE,
+	STATE_BIT_SPACE,
+	STATE_TRAILER_PULSE,
+	STATE_TRAILER_SPACE,
+};
+
+/**
+ * ir_nec_decode() - Decode one NEC 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_nec_decode(struct rc_dev *dev, struct ir_raw_event ev)
+{
+	struct nec_dec *data = &dev->raw->nec;
+	u32 scancode;
+	enum rc_proto rc_proto;
+	u8 address, not_address, command, not_command;
+
+	if (!is_timing_event(ev)) {
+		if (ev.overflow)
+			data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	dev_dbg(&dev->dev, "NEC 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, NEC_HEADER_PULSE, NEC_UNIT * 2)) {
+			data->is_nec_x = false;
+			data->necx_repeat = false;
+		} else if (eq_margin(ev.duration, NECX_HEADER_PULSE, NEC_UNIT / 2))
+			data->is_nec_x = true;
+		else
+			break;
+
+		data->count = 0;
+		data->state = STATE_HEADER_SPACE;
+		return 0;
+
+	case STATE_HEADER_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (eq_margin(ev.duration, NEC_HEADER_SPACE, NEC_UNIT)) {
+			data->state = STATE_BIT_PULSE;
+			return 0;
+		} else if (eq_margin(ev.duration, NEC_REPEAT_SPACE, NEC_UNIT / 2)) {
+			data->state = STATE_TRAILER_PULSE;
+			return 0;
+		}
+
+		break;
+
+	case STATE_BIT_PULSE:
+		if (!ev.pulse)
+			break;
+
+		if (!eq_margin(ev.duration, NEC_BIT_PULSE, NEC_UNIT / 2))
+			break;
+
+		data->state = STATE_BIT_SPACE;
+		return 0;
+
+	case STATE_BIT_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (data->necx_repeat && data->count == NECX_REPEAT_BITS &&
+		    geq_margin(ev.duration, NEC_TRAILER_SPACE, NEC_UNIT / 2)) {
+			dev_dbg(&dev->dev, "Repeat last key\n");
+			rc_repeat(dev);
+			data->state = STATE_INACTIVE;
+			return 0;
+		} else if (data->count > NECX_REPEAT_BITS)
+			data->necx_repeat = false;
+
+		data->bits <<= 1;
+		if (eq_margin(ev.duration, NEC_BIT_1_SPACE, NEC_UNIT / 2))
+			data->bits |= 1;
+		else if (!eq_margin(ev.duration, NEC_BIT_0_SPACE, NEC_UNIT / 2))
+			break;
+		data->count++;
+
+		if (data->count == NEC_NBITS)
+			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, NEC_TRAILER_PULSE, NEC_UNIT / 2))
+			break;
+
+		data->state = STATE_TRAILER_SPACE;
+		return 0;
+
+	case STATE_TRAILER_SPACE:
+		if (ev.pulse)
+			break;
+
+		if (!geq_margin(ev.duration, NEC_TRAILER_SPACE, NEC_UNIT / 2))
+			break;
+
+		if (data->count == NEC_NBITS) {
+			address     = bitrev8((data->bits >> 24) & 0xff);
+			not_address = bitrev8((data->bits >> 16) & 0xff);
+			command	    = bitrev8((data->bits >>  8) & 0xff);
+			not_command = bitrev8((data->bits >>  0) & 0xff);
+
+			scancode = ir_nec_bytes_to_scancode(address,
+							    not_address,
+							    command,
+							    not_command,
+							    &rc_proto);
+
+			if (data->is_nec_x)
+				data->necx_repeat = true;
+
+			rc_keydown(dev, rc_proto, scancode, 0);
+		} else {
+			rc_repeat(dev);
+		}
+
+		data->state = STATE_INACTIVE;
+		return 0;
+	}
+
+	dev_dbg(&dev->dev, "NEC 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;
+}
+
+/**
+ * ir_nec_scancode_to_raw() - encode an NEC scancode ready for modulation.
+ * @protocol:	specific protocol to use
+ * @scancode:	a single NEC scancode.
+ */
+static u32 ir_nec_scancode_to_raw(enum rc_proto protocol, u32 scancode)
+{
+	unsigned int addr, addr_inv, data, data_inv;
+
+	data = scancode & 0xff;
+
+	if (protocol == RC_PROTO_NEC32) {
+		/* 32-bit NEC (used by Apple and TiVo remotes) */
+		/* scan encoding: aaAAddDD */
+		addr_inv   = (scancode >> 24) & 0xff;
+		addr       = (scancode >> 16) & 0xff;
+		data_inv   = (scancode >>  8) & 0xff;
+	} else if (protocol == RC_PROTO_NECX) {
+		/* Extended NEC */
+		/* scan encoding AAaaDD */
+		addr       = (scancode >> 16) & 0xff;
+		addr_inv   = (scancode >>  8) & 0xff;
+		data_inv   = data ^ 0xff;
+	} else {
+		/* Normal NEC */
+		/* scan encoding: AADD */
+		addr       = (scancode >>  8) & 0xff;
+		addr_inv   = addr ^ 0xff;
+		data_inv   = data ^ 0xff;
+	}
+
+	/* raw encoding: ddDDaaAA */
+	return data_inv << 24 |
+	       data     << 16 |
+	       addr_inv <<  8 |
+	       addr;
+}
+
+static const struct ir_raw_timings_pd ir_nec_timings = {
+	.header_pulse	= NEC_HEADER_PULSE,
+	.header_space	= NEC_HEADER_SPACE,
+	.bit_pulse	= NEC_BIT_PULSE,
+	.bit_space[0]	= NEC_BIT_0_SPACE,
+	.bit_space[1]	= NEC_BIT_1_SPACE,
+	.trailer_pulse	= NEC_TRAILER_PULSE,
+	.trailer_space	= NEC_TRAILER_SPACE,
+	.msb_first	= 0,
+};
+
+/**
+ * ir_nec_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_nec_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;
+
+	/* Convert a NEC scancode to raw NEC data */
+	raw = ir_nec_scancode_to_raw(protocol, scancode);
+
+	/* Modulate the raw data using a pulse distance modulation */
+	ret = ir_raw_gen_pd(&e, max, &ir_nec_timings, NEC_NBITS, raw);
+	if (ret < 0)
+		return ret;
+
+	return e - events;
+}
+
+static struct ir_raw_handler nec_handler = {
+	.protocols	= RC_PROTO_BIT_NEC | RC_PROTO_BIT_NECX |
+							RC_PROTO_BIT_NEC32,
+	.decode		= ir_nec_decode,
+	.encode		= ir_nec_encode,
+	.carrier	= 38000,
+	.min_timeout	= NEC_TRAILER_SPACE,
+};
+
+static int __init ir_nec_decode_init(void)
+{
+	ir_raw_handler_register(&nec_handler);
+
+	printk(KERN_INFO "IR NEC protocol handler initialized\n");
+	return 0;
+}
+
+static void __exit ir_nec_decode_exit(void)
+{
+	ir_raw_handler_unregister(&nec_handler);
+}
+
+module_init(ir_nec_decode_init);
+module_exit(ir_nec_decode_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Mauro Carvalho Chehab");
+MODULE_AUTHOR("Red Hat Inc. (http://www.redhat.com)");
+MODULE_DESCRIPTION("NEC IR protocol decoder");