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/dvb-frontends/a8293.c b/drivers/media/dvb-frontends/a8293.c
new file mode 100644
index 000000000..52e3dc928
--- /dev/null
+++ b/drivers/media/dvb-frontends/a8293.c
@@ -0,0 +1,278 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Allegro A8293 SEC driver
+ *
+ * Copyright (C) 2011 Antti Palosaari <crope@iki.fi>
+ */
+
+#include "a8293.h"
+
+#define A8293_FLAG_ODT			0x10
+
+struct a8293_dev {
+	struct i2c_client *client;
+	u8 reg[2];
+	int volt_slew_nanos_per_mv;
+};
+
+/*
+ * When increasing voltage, do so in minimal steps over time, minimizing
+ * risk of vIN undervoltage.
+ */
+
+static int a8293_set_voltage_slew(struct a8293_dev *dev,
+				  struct i2c_client *client,
+				  enum fe_sec_voltage fe_sec_voltage,
+				  int min_nanos_per_mv)
+{
+	int ret;
+	u8 reg0, reg1;
+	int new_volt_idx;
+	const int idx_to_mv[] = {
+		0,    12709, 13042, 13375, 14042, 15042, 18042, 18709, 19042
+	};
+	const u8 idx_to_reg[] = {
+		0x00, 0x20,  0x21,  0x22,  0x24,  0x27,  0x28,  0x2A,  0x2B
+	};
+	int this_volt_idx;
+	u8 status;
+	int prev_volt_idx;
+
+	dev_dbg(&client->dev, "set_voltage_slew fe_sec_voltage=%d\n",
+		fe_sec_voltage);
+
+	/* Read status register to clear any stale faults. */
+	ret = i2c_master_recv(client, &status, 1);
+	if (ret < 0)
+		goto err;
+
+	/* Determine previous voltage */
+	switch (dev->reg[0] & 0x2F) {
+	case 0x00:
+		prev_volt_idx = 0;
+		break;
+	case 0x20:
+		prev_volt_idx = 1;
+		break;
+	case 0x21:
+		prev_volt_idx = 2;
+		break;
+	case 0x22:
+		prev_volt_idx = 3;
+		break;
+	case 0x24:
+		prev_volt_idx = 4;
+		break;
+	case 0x27:
+		prev_volt_idx = 5;
+		break;
+	case 0x28:
+		prev_volt_idx = 6;
+		break;
+	case 0x2A:
+		prev_volt_idx = 7;
+		break;
+	case 0x2B:
+		prev_volt_idx = 8;
+		break;
+	default:
+		prev_volt_idx = 0;
+	}
+
+	/* Determine new voltage */
+	switch (fe_sec_voltage) {
+	case SEC_VOLTAGE_OFF:
+		new_volt_idx = 0;
+		break;
+	case SEC_VOLTAGE_13:
+		new_volt_idx = 2;
+		break;
+	case SEC_VOLTAGE_18:
+		new_volt_idx = 6;
+		break;
+	default:
+		ret = -EINVAL;
+		goto err;
+	}
+
+	/* Slew to new voltage if new voltage is greater than current voltage */
+	this_volt_idx = prev_volt_idx;
+	if (this_volt_idx < new_volt_idx) {
+		while (this_volt_idx < new_volt_idx) {
+			int delta_mv = idx_to_mv[this_volt_idx+1] - idx_to_mv[this_volt_idx];
+			int min_wait_time = delta_mv * min_nanos_per_mv;
+
+			reg0 = idx_to_reg[this_volt_idx+1];
+			reg0 |= A8293_FLAG_ODT;
+
+			ret = i2c_master_send(client, &reg0, 1);
+			if (ret < 0)
+				goto err;
+			dev->reg[0] = reg0;
+			this_volt_idx++;
+			usleep_range(min_wait_time, min_wait_time * 2);
+		}
+	} else { /* Else just set the voltage */
+		reg0 = idx_to_reg[new_volt_idx];
+		reg0 |= A8293_FLAG_ODT;
+		ret = i2c_master_send(client, &reg0, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[0] = reg0;
+	}
+
+	/* TMODE=0, TGATE=1 */
+	reg1 = 0x82;
+	if (reg1 != dev->reg[1]) {
+		ret = i2c_master_send(client, &reg1, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[1] = reg1;
+	}
+
+	usleep_range(1500, 5000);
+
+	return 0;
+err:
+	dev_dbg(&client->dev, "failed=%d\n", ret);
+	return ret;
+}
+
+
+static int a8293_set_voltage_noslew(struct dvb_frontend *fe,
+				    enum fe_sec_voltage fe_sec_voltage)
+{
+	struct a8293_dev *dev = fe->sec_priv;
+	struct i2c_client *client = dev->client;
+	int ret;
+	u8 reg0, reg1;
+
+	dev_dbg(&client->dev, "set_voltage_noslew fe_sec_voltage=%d\n",
+		fe_sec_voltage);
+
+	switch (fe_sec_voltage) {
+	case SEC_VOLTAGE_OFF:
+		/* ENB=0 */
+		reg0 = 0x10;
+		break;
+	case SEC_VOLTAGE_13:
+		/* VSEL0=1, VSEL1=0, VSEL2=0, VSEL3=0, ENB=1*/
+		reg0 = 0x31;
+		break;
+	case SEC_VOLTAGE_18:
+		/* VSEL0=0, VSEL1=0, VSEL2=0, VSEL3=1, ENB=1*/
+		reg0 = 0x38;
+		break;
+	default:
+		ret = -EINVAL;
+		goto err;
+	}
+	if (reg0 != dev->reg[0]) {
+		ret = i2c_master_send(client, &reg0, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[0] = reg0;
+	}
+
+	/* TMODE=0, TGATE=1 */
+	reg1 = 0x82;
+	if (reg1 != dev->reg[1]) {
+		ret = i2c_master_send(client, &reg1, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[1] = reg1;
+	}
+
+	usleep_range(1500, 50000);
+	return 0;
+err:
+	dev_dbg(&client->dev, "failed=%d\n", ret);
+	return ret;
+}
+
+static int a8293_set_voltage(struct dvb_frontend *fe,
+			     enum fe_sec_voltage fe_sec_voltage)
+{
+	struct a8293_dev *dev = fe->sec_priv;
+	struct i2c_client *client = dev->client;
+	int volt_slew_nanos_per_mv = dev->volt_slew_nanos_per_mv;
+
+	dev_dbg(&client->dev, "set_voltage volt_slew_nanos_per_mv=%d\n",
+		volt_slew_nanos_per_mv);
+
+	/* Use slew version if slew rate is set to a sane value */
+	if (volt_slew_nanos_per_mv > 0 && volt_slew_nanos_per_mv < 1600)
+		a8293_set_voltage_slew(dev, client, fe_sec_voltage,
+				       volt_slew_nanos_per_mv);
+	else
+		a8293_set_voltage_noslew(fe, fe_sec_voltage);
+
+	return 0;
+}
+
+static int a8293_probe(struct i2c_client *client)
+{
+	struct a8293_dev *dev;
+	struct a8293_platform_data *pdata = client->dev.platform_data;
+	struct dvb_frontend *fe = pdata->dvb_frontend;
+	int ret;
+	u8 buf[2];
+
+	dev = kzalloc_obj(*dev);
+	if (!dev) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	dev->client = client;
+	dev->volt_slew_nanos_per_mv = pdata->volt_slew_nanos_per_mv;
+
+	/* check if the SEC is there */
+	ret = i2c_master_recv(client, buf, 2);
+	if (ret < 0)
+		goto err_kfree;
+
+	/* override frontend ops */
+	fe->ops.set_voltage = a8293_set_voltage;
+	fe->sec_priv = dev;
+	i2c_set_clientdata(client, dev);
+
+	dev_info(&client->dev, "Allegro A8293 SEC successfully attached\n");
+	return 0;
+err_kfree:
+	kfree(dev);
+err:
+	dev_dbg(&client->dev, "failed=%d\n", ret);
+	return ret;
+}
+
+static void a8293_remove(struct i2c_client *client)
+{
+	struct a8293_dev *dev = i2c_get_clientdata(client);
+
+	dev_dbg(&client->dev, "\n");
+
+	kfree(dev);
+}
+
+static const struct i2c_device_id a8293_id_table[] = {
+	{ .name = "a8293" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, a8293_id_table);
+
+static struct i2c_driver a8293_driver = {
+	.driver = {
+		.name	= "a8293",
+		.suppress_bind_attrs = true,
+	},
+	.probe		= a8293_probe,
+	.remove		= a8293_remove,
+	.id_table	= a8293_id_table,
+};
+
+module_i2c_driver(a8293_driver);
+
+MODULE_AUTHOR("Antti Palosaari <crope@iki.fi>");
+MODULE_DESCRIPTION("Allegro A8293 SEC driver");
+MODULE_LICENSE("GPL");