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, 154 insertions, 0 deletions

diff --git a/arch/mips/ralink/timer.c b/arch/mips/ralink/timer.c
new file mode 100644
index 000000000..06bc2c014
--- /dev/null
+++ b/arch/mips/ralink/timer.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Ralink RT2880 timer
+ * Author: John Crispin
+ *
+ * Copyright (C) 2013 John Crispin <john@phrozen.org>
+*/
+
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/platform_device.h>
+#include <linux/timer.h>
+#include <linux/types.h>
+
+#include <asm/mach-ralink/ralink_regs.h>
+
+#define TIMER_REG_TMRSTAT		0x00
+#define TIMER_REG_TMR0LOAD		0x10
+#define TIMER_REG_TMR0CTL		0x18
+
+#define TMRSTAT_TMR0INT			BIT(0)
+
+#define TMR0CTL_ENABLE			BIT(7)
+#define TMR0CTL_MODE_PERIODIC		BIT(4)
+#define TMR0CTL_PRESCALER		1
+#define TMR0CTL_PRESCALE_VAL		(0xf - TMR0CTL_PRESCALER)
+#define TMR0CTL_PRESCALE_DIV		(65536 / BIT(TMR0CTL_PRESCALER))
+
+struct rt_timer {
+	struct device	*dev;
+	void __iomem	*membase;
+	int		irq;
+	unsigned long	timer_freq;
+	unsigned long	timer_div;
+};
+
+static inline void rt_timer_w32(struct rt_timer *rt, u8 reg, u32 val)
+{
+	__raw_writel(val, rt->membase + reg);
+}
+
+static inline u32 rt_timer_r32(struct rt_timer *rt, u8 reg)
+{
+	return __raw_readl(rt->membase + reg);
+}
+
+static irqreturn_t rt_timer_irq(int irq, void *_rt)
+{
+	struct rt_timer *rt =  (struct rt_timer *) _rt;
+
+	rt_timer_w32(rt, TIMER_REG_TMR0LOAD, rt->timer_freq / rt->timer_div);
+	rt_timer_w32(rt, TIMER_REG_TMRSTAT, TMRSTAT_TMR0INT);
+
+	return IRQ_HANDLED;
+}
+
+
+static int rt_timer_request(struct rt_timer *rt)
+{
+	int err = request_irq(rt->irq, rt_timer_irq, 0,
+						dev_name(rt->dev), rt);
+	if (err) {
+		dev_err(rt->dev, "failed to request irq\n");
+	} else {
+		u32 t = TMR0CTL_MODE_PERIODIC | TMR0CTL_PRESCALE_VAL;
+		rt_timer_w32(rt, TIMER_REG_TMR0CTL, t);
+	}
+	return err;
+}
+
+static int rt_timer_config(struct rt_timer *rt, unsigned long divisor)
+{
+	if (rt->timer_freq < divisor)
+		rt->timer_div = rt->timer_freq;
+	else
+		rt->timer_div = divisor;
+
+	rt_timer_w32(rt, TIMER_REG_TMR0LOAD, rt->timer_freq / rt->timer_div);
+
+	return 0;
+}
+
+static int rt_timer_enable(struct rt_timer *rt)
+{
+	u32 t;
+
+	rt_timer_w32(rt, TIMER_REG_TMR0LOAD, rt->timer_freq / rt->timer_div);
+
+	t = rt_timer_r32(rt, TIMER_REG_TMR0CTL);
+	t |= TMR0CTL_ENABLE;
+	rt_timer_w32(rt, TIMER_REG_TMR0CTL, t);
+
+	return 0;
+}
+
+static int rt_timer_probe(struct platform_device *pdev)
+{
+	struct rt_timer *rt;
+	struct clk *clk;
+
+	rt = devm_kzalloc(&pdev->dev, sizeof(*rt), GFP_KERNEL);
+	if (!rt) {
+		dev_err(&pdev->dev, "failed to allocate memory\n");
+		return -ENOMEM;
+	}
+
+	rt->irq = platform_get_irq(pdev, 0);
+	if (rt->irq < 0)
+		return rt->irq;
+
+	rt->membase = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
+	if (IS_ERR(rt->membase))
+		return PTR_ERR(rt->membase);
+
+	clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(&pdev->dev, "failed get clock rate\n");
+		return PTR_ERR(clk);
+	}
+
+	rt->timer_freq = clk_get_rate(clk) / TMR0CTL_PRESCALE_DIV;
+	if (!rt->timer_freq)
+		return -EINVAL;
+
+	rt->dev = &pdev->dev;
+	platform_set_drvdata(pdev, rt);
+
+	rt_timer_request(rt);
+	rt_timer_config(rt, 2);
+	rt_timer_enable(rt);
+
+	dev_info(&pdev->dev, "maximum frequency is %luHz\n", rt->timer_freq);
+
+	return 0;
+}
+
+static const struct of_device_id rt_timer_match[] = {
+	{ .compatible = "ralink,rt2880-timer" },
+	{},
+};
+
+static struct platform_driver rt_timer_driver = {
+	.probe = rt_timer_probe,
+	.driver = {
+		.name			= "rt-timer",
+		.of_match_table		= rt_timer_match,
+		.suppress_bind_attrs	= true,
+	},
+};
+builtin_platform_driver(rt_timer_driver);