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, 331 insertions, 0 deletions

diff --git a/drivers/media/dvb-frontends/ec100.c b/drivers/media/dvb-frontends/ec100.c
new file mode 100644
index 000000000..b7a3572f8
--- /dev/null
+++ b/drivers/media/dvb-frontends/ec100.c
@@ -0,0 +1,331 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * E3C EC100 demodulator driver
+ *
+ * Copyright (C) 2009 Antti Palosaari <crope@iki.fi>
+ */
+
+#include <media/dvb_frontend.h>
+#include "ec100.h"
+
+struct ec100_state {
+	struct i2c_adapter *i2c;
+	struct dvb_frontend frontend;
+	struct ec100_config config;
+
+	u16 ber;
+};
+
+/* write single register */
+static int ec100_write_reg(struct ec100_state *state, u8 reg, u8 val)
+{
+	int ret;
+	u8 buf[2] = {reg, val};
+	struct i2c_msg msg[1] = {
+		{
+			.addr = state->config.demod_address,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf,
+		}
+	};
+
+	ret = i2c_transfer(state->i2c, msg, 1);
+	if (ret == 1) {
+		ret = 0;
+	} else {
+		dev_warn(&state->i2c->dev, "%s: i2c wr failed=%d reg=%02x\n",
+				KBUILD_MODNAME, ret, reg);
+		ret = -EREMOTEIO;
+	}
+
+	return ret;
+}
+
+/* read single register */
+static int ec100_read_reg(struct ec100_state *state, u8 reg, u8 *val)
+{
+	int ret;
+	struct i2c_msg msg[2] = {
+		{
+			.addr = state->config.demod_address,
+			.flags = 0,
+			.len = 1,
+			.buf = &reg
+		}, {
+			.addr = state->config.demod_address,
+			.flags = I2C_M_RD,
+			.len = 1,
+			.buf = val
+		}
+	};
+
+	ret = i2c_transfer(state->i2c, msg, 2);
+	if (ret == 2) {
+		ret = 0;
+	} else {
+		dev_warn(&state->i2c->dev, "%s: i2c rd failed=%d reg=%02x\n",
+				KBUILD_MODNAME, ret, reg);
+		ret = -EREMOTEIO;
+	}
+
+	return ret;
+}
+
+static int ec100_set_frontend(struct dvb_frontend *fe)
+{
+	struct dtv_frontend_properties *c = &fe->dtv_property_cache;
+	struct ec100_state *state = fe->demodulator_priv;
+	int ret;
+	u8 tmp, tmp2;
+
+	dev_dbg(&state->i2c->dev, "%s: frequency=%d bandwidth_hz=%d\n",
+			__func__, c->frequency, c->bandwidth_hz);
+
+	/* program tuner */
+	if (fe->ops.tuner_ops.set_params)
+		fe->ops.tuner_ops.set_params(fe);
+
+	ret = ec100_write_reg(state, 0x04, 0x06);
+	if (ret)
+		goto error;
+	ret = ec100_write_reg(state, 0x67, 0x58);
+	if (ret)
+		goto error;
+	ret = ec100_write_reg(state, 0x05, 0x18);
+	if (ret)
+		goto error;
+
+	/* reg/bw |   6  |   7  |   8
+	   -------+------+------+------
+	   A 0x1b | 0xa1 | 0xe7 | 0x2c
+	   A 0x1c | 0x55 | 0x63 | 0x72
+	   -------+------+------+------
+	   B 0x1b | 0xb7 | 0x00 | 0x49
+	   B 0x1c | 0x55 | 0x64 | 0x72 */
+
+	switch (c->bandwidth_hz) {
+	case 6000000:
+		tmp = 0xb7;
+		tmp2 = 0x55;
+		break;
+	case 7000000:
+		tmp = 0x00;
+		tmp2 = 0x64;
+		break;
+	case 8000000:
+	default:
+		tmp = 0x49;
+		tmp2 = 0x72;
+	}
+
+	ret = ec100_write_reg(state, 0x1b, tmp);
+	if (ret)
+		goto error;
+	ret = ec100_write_reg(state, 0x1c, tmp2);
+	if (ret)
+		goto error;
+
+	ret = ec100_write_reg(state, 0x0c, 0xbb); /* if freq */
+	if (ret)
+		goto error;
+	ret = ec100_write_reg(state, 0x0d, 0x31); /* if freq */
+	if (ret)
+		goto error;
+
+	ret = ec100_write_reg(state, 0x08, 0x24);
+	if (ret)
+		goto error;
+
+	ret = ec100_write_reg(state, 0x00, 0x00); /* go */
+	if (ret)
+		goto error;
+	ret = ec100_write_reg(state, 0x00, 0x20); /* go */
+	if (ret)
+		goto error;
+
+	return ret;
+error:
+	dev_dbg(&state->i2c->dev, "%s: failed=%d\n", __func__, ret);
+	return ret;
+}
+
+static int ec100_get_tune_settings(struct dvb_frontend *fe,
+	struct dvb_frontend_tune_settings *fesettings)
+{
+	fesettings->min_delay_ms = 300;
+	fesettings->step_size = 0;
+	fesettings->max_drift = 0;
+
+	return 0;
+}
+
+static int ec100_read_status(struct dvb_frontend *fe, enum fe_status *status)
+{
+	struct ec100_state *state = fe->demodulator_priv;
+	int ret;
+	u8 tmp;
+	*status = 0;
+
+	ret = ec100_read_reg(state, 0x42, &tmp);
+	if (ret)
+		goto error;
+
+	if (tmp & 0x80) {
+		/* bit7 set - have lock */
+		*status |= FE_HAS_SIGNAL | FE_HAS_CARRIER | FE_HAS_VITERBI |
+			FE_HAS_SYNC | FE_HAS_LOCK;
+	} else {
+		ret = ec100_read_reg(state, 0x01, &tmp);
+		if (ret)
+			goto error;
+
+		if (tmp & 0x10) {
+			/* bit4 set - have signal */
+			*status |= FE_HAS_SIGNAL;
+			if (!(tmp & 0x01)) {
+				/* bit0 clear - have ~valid signal */
+				*status |= FE_HAS_CARRIER |  FE_HAS_VITERBI;
+			}
+		}
+	}
+
+	return ret;
+error:
+	dev_dbg(&state->i2c->dev, "%s: failed=%d\n", __func__, ret);
+	return ret;
+}
+
+static int ec100_read_ber(struct dvb_frontend *fe, u32 *ber)
+{
+	struct ec100_state *state = fe->demodulator_priv;
+	int ret;
+	u8 tmp, tmp2;
+	u16 ber2;
+
+	*ber = 0;
+
+	ret = ec100_read_reg(state, 0x65, &tmp);
+	if (ret)
+		goto error;
+	ret = ec100_read_reg(state, 0x66, &tmp2);
+	if (ret)
+		goto error;
+
+	ber2 = (tmp2 << 8) | tmp;
+
+	/* if counter overflow or clear */
+	if (ber2 < state->ber)
+		*ber = ber2;
+	else
+		*ber = ber2 - state->ber;
+
+	state->ber = ber2;
+
+	return ret;
+error:
+	dev_dbg(&state->i2c->dev, "%s: failed=%d\n", __func__, ret);
+	return ret;
+}
+
+static int ec100_read_signal_strength(struct dvb_frontend *fe, u16 *strength)
+{
+	struct ec100_state *state = fe->demodulator_priv;
+	int ret;
+	u8 tmp;
+
+	ret = ec100_read_reg(state, 0x24, &tmp);
+	if (ret) {
+		*strength = 0;
+		goto error;
+	}
+
+	*strength = ((tmp << 8) | tmp);
+
+	return ret;
+error:
+	dev_dbg(&state->i2c->dev, "%s: failed=%d\n", __func__, ret);
+	return ret;
+}
+
+static int ec100_read_snr(struct dvb_frontend *fe, u16 *snr)
+{
+	*snr = 0;
+	return 0;
+}
+
+static int ec100_read_ucblocks(struct dvb_frontend *fe, u32 *ucblocks)
+{
+	*ucblocks = 0;
+	return 0;
+}
+
+static void ec100_release(struct dvb_frontend *fe)
+{
+	struct ec100_state *state = fe->demodulator_priv;
+	kfree(state);
+}
+
+static const struct dvb_frontend_ops ec100_ops;
+
+struct dvb_frontend *ec100_attach(const struct ec100_config *config,
+	struct i2c_adapter *i2c)
+{
+	int ret;
+	struct ec100_state *state = NULL;
+	u8 tmp;
+
+	/* allocate memory for the internal state */
+	state = kzalloc_obj(struct ec100_state);
+	if (state == NULL)
+		goto error;
+
+	/* setup the state */
+	state->i2c = i2c;
+	memcpy(&state->config, config, sizeof(struct ec100_config));
+
+	/* check if the demod is there */
+	ret = ec100_read_reg(state, 0x33, &tmp);
+	if (ret || tmp != 0x0b)
+		goto error;
+
+	/* create dvb_frontend */
+	memcpy(&state->frontend.ops, &ec100_ops,
+		sizeof(struct dvb_frontend_ops));
+	state->frontend.demodulator_priv = state;
+
+	return &state->frontend;
+error:
+	kfree(state);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ec100_attach);
+
+static const struct dvb_frontend_ops ec100_ops = {
+	.delsys = { SYS_DVBT },
+	.info = {
+		.name = "E3C EC100 DVB-T",
+		.caps =
+			FE_CAN_FEC_1_2 | FE_CAN_FEC_2_3 | FE_CAN_FEC_3_4 |
+			FE_CAN_FEC_5_6 | FE_CAN_FEC_7_8 | FE_CAN_FEC_AUTO |
+			FE_CAN_QPSK | FE_CAN_QAM_16 |
+			FE_CAN_QAM_64 | FE_CAN_QAM_AUTO |
+			FE_CAN_TRANSMISSION_MODE_AUTO |
+			FE_CAN_GUARD_INTERVAL_AUTO |
+			FE_CAN_HIERARCHY_AUTO |
+			FE_CAN_MUTE_TS
+	},
+
+	.release = ec100_release,
+	.set_frontend = ec100_set_frontend,
+	.get_tune_settings = ec100_get_tune_settings,
+	.read_status = ec100_read_status,
+	.read_ber = ec100_read_ber,
+	.read_signal_strength = ec100_read_signal_strength,
+	.read_snr = ec100_read_snr,
+	.read_ucblocks = ec100_read_ucblocks,
+};
+
+MODULE_AUTHOR("Antti Palosaari <crope@iki.fi>");
+MODULE_DESCRIPTION("E3C EC100 DVB-T demodulator driver");
+MODULE_LICENSE("GPL");