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, 178 insertions, 0 deletions

diff --git a/sound/drivers/virmidi.c b/sound/drivers/virmidi.c
new file mode 100644
index 000000000..70e16105f
--- /dev/null
+++ b/sound/drivers/virmidi.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Dummy soundcard for virtual rawmidi devices
+ *
+ *  Copyright (c) 2000 by Takashi Iwai <tiwai@suse.de>
+ */
+
+/*
+ * VIRTUAL RAW MIDI DEVICE CARDS
+ *
+ * This dummy card contains up to 4 virtual rawmidi devices.
+ * They are not real rawmidi devices but just associated with sequencer
+ * clients, so that any input/output sources can be connected as a raw
+ * MIDI device arbitrary.
+ * Also, multiple access is allowed to a single rawmidi device.
+ *
+ * Typical usage is like following:
+ * - Load snd-virmidi module.
+ *	# modprobe snd-virmidi index=2
+ *   Then, sequencer clients 72:0 to 75:0 will be created, which are
+ *   mapped from /dev/snd/midiC1D0 to /dev/snd/midiC1D3, respectively.
+ *
+ * - Connect input/output via aconnect.
+ *	% aconnect 64:0 72:0	# keyboard input redirection 64:0 -> 72:0
+ *	% aconnect 72:0 65:0	# output device redirection 72:0 -> 65:0
+ *
+ * - Run application using a midi device (eg. /dev/snd/midiC1D0)
+ */
+
+#include <linux/init.h>
+#include <linux/wait.h>
+#include <linux/err.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/seq_kernel.h>
+#include <sound/seq_virmidi.h>
+#include <sound/initval.h>
+
+/* hack: OSS defines midi_devs, so undefine it (versioned symbols) */
+#undef midi_devs
+
+MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
+MODULE_DESCRIPTION("Dummy soundcard for virtual rawmidi devices");
+MODULE_LICENSE("GPL");
+
+#define MAX_MIDI_DEVICES	4
+
+static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;	/* Index 0-MAX */
+static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;	/* ID for this card */
+static bool enable[SNDRV_CARDS] = {1, [1 ... (SNDRV_CARDS - 1)] = 0};
+static int midi_devs[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 4};
+
+module_param_array(index, int, NULL, 0444);
+MODULE_PARM_DESC(index, "Index value for virmidi soundcard.");
+module_param_array(id, charp, NULL, 0444);
+MODULE_PARM_DESC(id, "ID string for virmidi soundcard.");
+module_param_array(enable, bool, NULL, 0444);
+MODULE_PARM_DESC(enable, "Enable this soundcard.");
+module_param_array(midi_devs, int, NULL, 0444);
+MODULE_PARM_DESC(midi_devs, "MIDI devices # (1-4)");
+
+struct snd_card_virmidi {
+	struct snd_card *card;
+	struct snd_rawmidi *midi[MAX_MIDI_DEVICES];
+};
+
+static struct platform_device *devices[SNDRV_CARDS];
+
+
+static int snd_virmidi_probe(struct platform_device *devptr)
+{
+	struct snd_card *card;
+	struct snd_card_virmidi *vmidi;
+	int idx, err;
+	int dev = devptr->id;
+
+	if (dev < 0 || dev >= SNDRV_CARDS) {
+		dev_warn(&devptr->dev,
+			 "Invalid card index %d, using default 0\n", dev);
+		dev = 0;
+	}
+
+	err = snd_devm_card_new(&devptr->dev, index[dev], id[dev], THIS_MODULE,
+				sizeof(struct snd_card_virmidi), &card);
+	if (err < 0)
+		return err;
+	vmidi = card->private_data;
+	vmidi->card = card;
+
+	if (midi_devs[dev] > MAX_MIDI_DEVICES) {
+		dev_warn(&devptr->dev,
+			 "too much midi devices for virmidi %d: force to use %d\n",
+			 dev, MAX_MIDI_DEVICES);
+		midi_devs[dev] = MAX_MIDI_DEVICES;
+	}
+	for (idx = 0; idx < midi_devs[dev]; idx++) {
+		struct snd_rawmidi *rmidi;
+
+		err = snd_virmidi_new(card, idx, &rmidi);
+		if (err < 0)
+			return err;
+		vmidi->midi[idx] = rmidi;
+		strscpy(rmidi->name, "Virtual Raw MIDI");
+	}
+
+	strscpy(card->driver, "VirMIDI");
+	strscpy(card->shortname, "VirMIDI");
+	sprintf(card->longname, "Virtual MIDI Card %i", dev + 1);
+
+	err = snd_card_register(card);
+	if (err)
+		return err;
+
+	platform_set_drvdata(devptr, card);
+	return 0;
+}
+
+#define SND_VIRMIDI_DRIVER	"snd_virmidi"
+
+static struct platform_driver snd_virmidi_driver = {
+	.probe		= snd_virmidi_probe,
+	.driver		= {
+		.name	= SND_VIRMIDI_DRIVER,
+	},
+};
+
+static void snd_virmidi_unregister_all(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(devices); ++i)
+		platform_device_unregister(devices[i]);
+	platform_driver_unregister(&snd_virmidi_driver);
+}
+
+static int __init alsa_card_virmidi_init(void)
+{
+	int i, cards, err;
+
+	err = platform_driver_register(&snd_virmidi_driver);
+	if (err < 0)
+		return err;
+
+	cards = 0;
+	for (i = 0; i < SNDRV_CARDS; i++) {
+		struct platform_device *device;
+
+		if (!enable[i])
+			continue;
+		device = platform_device_register_simple(SND_VIRMIDI_DRIVER,
+							 i, NULL, 0);
+		if (IS_ERR(device))
+			continue;
+		if (!platform_get_drvdata(device)) {
+			platform_device_unregister(device);
+			continue;
+		}
+		devices[i] = device;
+		cards++;
+	}
+	if (!cards) {
+#ifdef MODULE
+		pr_err("Card-VirMIDI soundcard not found or device busy\n");
+#endif
+		snd_virmidi_unregister_all();
+		return -ENODEV;
+	}
+	return 0;
+}
+
+static void __exit alsa_card_virmidi_exit(void)
+{
+	snd_virmidi_unregister_all();
+}
+
+module_init(alsa_card_virmidi_init)
+module_exit(alsa_card_virmidi_exit)