kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 408 insertions, 0 deletions

diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
new file mode 100644
index 000000000..82404b6e2
--- /dev/null
+++ b/drivers/hid/hid-u2fzero.c
@@ -0,0 +1,408 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * U2F Zero LED and RNG driver
+ *
+ * Copyright 2018 Andrej Shadura <andrew@shadura.me>
+ * Loosely based on drivers/hid/hid-led.c
+ *              and drivers/usb/misc/chaoskey.c
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2.
+ */
+
+#include <linux/hid.h>
+#include <linux/hidraw.h>
+#include <linux/hw_random.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/usb.h>
+
+#include "usbhid/usbhid.h"
+#include "hid-ids.h"
+
+#define DRIVER_SHORT		"u2fzero"
+
+#define HID_REPORT_SIZE		64
+
+enum hw_revision {
+	HW_U2FZERO,
+	HW_NITROKEY_U2F,
+};
+
+struct hw_revision_config {
+	u8 rng_cmd;
+	u8 wink_cmd;
+	const char *name;
+};
+
+static const struct hw_revision_config hw_configs[] = {
+	[HW_U2FZERO] = {
+		.rng_cmd  = 0x21,
+		.wink_cmd = 0x24,
+		.name = "U2F Zero",
+	},
+	[HW_NITROKEY_U2F] = {
+		.rng_cmd  = 0xc0,
+		.wink_cmd = 0xc2,
+		.name = "NitroKey U2F",
+	},
+};
+
+/* We only use broadcast (CID-less) messages */
+#define CID_BROADCAST		0xffffffff
+
+struct u2f_hid_msg {
+	u32 cid;
+	union {
+		struct {
+			u8 cmd;
+			u8 bcnth;
+			u8 bcntl;
+			u8 data[HID_REPORT_SIZE - 7];
+		} init;
+		struct {
+			u8 seq;
+			u8 data[HID_REPORT_SIZE - 5];
+		} cont;
+	};
+} __packed;
+
+struct u2f_hid_report {
+	u8 report_type;
+	struct u2f_hid_msg msg;
+} __packed;
+
+#define U2F_HID_MSG_LEN(f)	(size_t)(((f).init.bcnth << 8) + (f).init.bcntl)
+
+struct u2fzero_device {
+	struct hid_device	*hdev;
+	struct urb		*urb;	    /* URB for the RNG data */
+	struct led_classdev	ldev;	    /* Embedded struct for led */
+	struct hwrng		hwrng;	    /* Embedded struct for hwrng */
+	char			*led_name;
+	char			*rng_name;
+	u8			*buf_out;
+	u8			*buf_in;
+	struct mutex		lock;
+	bool			present;
+	kernel_ulong_t		hw_revision;
+};
+
+static int u2fzero_send(struct u2fzero_device *dev, struct u2f_hid_report *req)
+{
+	int ret;
+
+	mutex_lock(&dev->lock);
+
+	memcpy(dev->buf_out, req, sizeof(struct u2f_hid_report));
+
+	ret = hid_hw_output_report(dev->hdev, dev->buf_out,
+				   sizeof(struct u2f_hid_msg));
+
+	mutex_unlock(&dev->lock);
+
+	if (ret < 0)
+		return ret;
+
+	return ret == sizeof(struct u2f_hid_msg) ? 0 : -EMSGSIZE;
+}
+
+struct u2fzero_transfer_context {
+	struct completion done;
+	int status;
+};
+
+static void u2fzero_read_callback(struct urb *urb)
+{
+	struct u2fzero_transfer_context *ctx = urb->context;
+
+	ctx->status = urb->status;
+	complete(&ctx->done);
+}
+
+static int u2fzero_recv(struct u2fzero_device *dev,
+			struct u2f_hid_report *req,
+			struct u2f_hid_msg *resp)
+{
+	int ret;
+	struct hid_device *hdev = dev->hdev;
+	struct u2fzero_transfer_context ctx;
+
+	mutex_lock(&dev->lock);
+
+	memcpy(dev->buf_out, req, sizeof(struct u2f_hid_report));
+
+	dev->urb->context = &ctx;
+	init_completion(&ctx.done);
+
+	ret = usb_submit_urb(dev->urb, GFP_NOIO);
+	if (unlikely(ret)) {
+		hid_err(hdev, "usb_submit_urb failed: %d", ret);
+		goto err;
+	}
+
+	ret = hid_hw_output_report(dev->hdev, dev->buf_out,
+				   sizeof(struct u2f_hid_msg));
+
+	if (ret < 0) {
+		hid_err(hdev, "hid_hw_output_report failed: %d", ret);
+		goto err;
+	}
+
+	ret = (wait_for_completion_timeout(
+		&ctx.done, msecs_to_jiffies(USB_CTRL_SET_TIMEOUT)));
+	if (ret == 0) {
+		usb_kill_urb(dev->urb);
+		hid_err(hdev, "urb submission timed out");
+	} else {
+		ret = dev->urb->actual_length;
+		memcpy(resp, dev->buf_in, ret);
+	}
+
+err:
+	mutex_unlock(&dev->lock);
+
+	return ret;
+}
+
+static int u2fzero_blink(struct led_classdev *ldev)
+{
+	struct u2fzero_device *dev = container_of(ldev,
+		struct u2fzero_device, ldev);
+	struct u2f_hid_report req = {
+		.report_type = 0,
+		.msg.cid = CID_BROADCAST,
+		.msg.init = {
+			.cmd = hw_configs[dev->hw_revision].wink_cmd,
+			.bcnth = 0,
+			.bcntl = 0,
+			.data  = {0},
+		}
+	};
+	return u2fzero_send(dev, &req);
+}
+
+static int u2fzero_brightness_set(struct led_classdev *ldev,
+				  enum led_brightness brightness)
+{
+	ldev->brightness = LED_OFF;
+	if (brightness)
+		return u2fzero_blink(ldev);
+	else
+		return 0;
+}
+
+static int u2fzero_rng_read(struct hwrng *rng, void *data,
+			    size_t max, bool wait)
+{
+	struct u2fzero_device *dev = container_of(rng,
+		struct u2fzero_device, hwrng);
+	struct u2f_hid_report req = {
+		.report_type = 0,
+		.msg.cid = CID_BROADCAST,
+		.msg.init = {
+			.cmd = hw_configs[dev->hw_revision].rng_cmd,
+			.bcnth = 0,
+			.bcntl = 0,
+			.data  = {0},
+		}
+	};
+	struct u2f_hid_msg resp;
+	int ret;
+	size_t actual_length;
+	/* valid packets must have a correct header */
+	int min_length = offsetof(struct u2f_hid_msg, init.data);
+
+	if (!dev->present) {
+		hid_dbg(dev->hdev, "device not present");
+		return 0;
+	}
+
+	ret = u2fzero_recv(dev, &req, &resp);
+
+	/* ignore errors or packets without data */
+	if (ret < min_length)
+		return 0;
+
+	/* only take the minimum amount of data it is safe to take */
+	actual_length = min3((size_t)ret - min_length,
+		U2F_HID_MSG_LEN(resp), max);
+
+	memcpy(data, resp.init.data, actual_length);
+
+	return actual_length;
+}
+
+static int u2fzero_init_led(struct u2fzero_device *dev,
+			    unsigned int minor)
+{
+	dev->led_name = devm_kasprintf(&dev->hdev->dev, GFP_KERNEL,
+		"%s%u", DRIVER_SHORT, minor);
+	if (dev->led_name == NULL)
+		return -ENOMEM;
+
+	dev->ldev.name = dev->led_name;
+	dev->ldev.max_brightness = LED_ON;
+	dev->ldev.flags = LED_HW_PLUGGABLE;
+	dev->ldev.brightness_set_blocking = u2fzero_brightness_set;
+
+	return devm_led_classdev_register(&dev->hdev->dev, &dev->ldev);
+}
+
+static int u2fzero_init_hwrng(struct u2fzero_device *dev,
+			      unsigned int minor)
+{
+	dev->rng_name = devm_kasprintf(&dev->hdev->dev, GFP_KERNEL,
+		"%s-rng%u", DRIVER_SHORT, minor);
+	if (dev->rng_name == NULL)
+		return -ENOMEM;
+
+	dev->hwrng.name = dev->rng_name;
+	dev->hwrng.read = u2fzero_rng_read;
+
+	return devm_hwrng_register(&dev->hdev->dev, &dev->hwrng);
+}
+
+static int u2fzero_fill_in_urb(struct u2fzero_device *dev)
+{
+	struct hid_device *hdev = dev->hdev;
+	struct usb_device *udev;
+	struct usbhid_device *usbhid = hdev->driver_data;
+	unsigned int pipe_in;
+	struct usb_host_endpoint *ep;
+
+	if (dev->hdev->bus != BUS_USB)
+		return -EINVAL;
+
+	udev = hid_to_usb_dev(hdev);
+
+	if (!usbhid->urbout || !usbhid->urbin)
+		return -ENODEV;
+
+	ep = usb_pipe_endpoint(udev, usbhid->urbin->pipe);
+	if (!ep)
+		return -ENODEV;
+
+	dev->urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!dev->urb)
+		return -ENOMEM;
+
+	pipe_in = (usbhid->urbin->pipe & ~(3 << 30)) | (PIPE_INTERRUPT << 30);
+
+	usb_fill_int_urb(dev->urb,
+		udev,
+		pipe_in,
+		dev->buf_in,
+		HID_REPORT_SIZE,
+		u2fzero_read_callback,
+		NULL,
+		ep->desc.bInterval);
+
+	return 0;
+}
+
+static int u2fzero_probe(struct hid_device *hdev,
+			 const struct hid_device_id *id)
+{
+	struct u2fzero_device *dev;
+	unsigned int minor;
+	int ret;
+
+	if (!hid_is_usb(hdev))
+		return -EINVAL;
+
+	dev = devm_kzalloc(&hdev->dev, sizeof(*dev), GFP_KERNEL);
+	if (dev == NULL)
+		return -ENOMEM;
+
+	dev->hw_revision = id->driver_data;
+
+	dev->buf_out = devm_kmalloc(&hdev->dev,
+		sizeof(struct u2f_hid_report), GFP_KERNEL);
+	if (dev->buf_out == NULL)
+		return -ENOMEM;
+
+	dev->buf_in = devm_kmalloc(&hdev->dev,
+		sizeof(struct u2f_hid_msg), GFP_KERNEL);
+	if (dev->buf_in == NULL)
+		return -ENOMEM;
+
+	ret = hid_parse(hdev);
+	if (ret)
+		return ret;
+
+	dev->hdev = hdev;
+	hid_set_drvdata(hdev, dev);
+	mutex_init(&dev->lock);
+
+	ret = hid_hw_start(hdev, HID_CONNECT_HIDRAW);
+	if (ret)
+		return ret;
+
+	ret = u2fzero_fill_in_urb(dev);
+	if (ret)
+		goto err_hid_hw_stop;
+
+	dev->present = true;
+
+	minor = ((struct hidraw *) hdev->hidraw)->minor;
+
+	ret = u2fzero_init_led(dev, minor);
+	if (ret)
+		goto err_free_urb;
+
+	hid_info(hdev, "%s LED initialised\n", hw_configs[dev->hw_revision].name);
+
+	ret = u2fzero_init_hwrng(dev, minor);
+	if (ret)
+		goto err_free_urb;
+
+	hid_info(hdev, "%s RNG initialised\n", hw_configs[dev->hw_revision].name);
+
+	return 0;
+
+err_free_urb:
+	usb_free_urb(dev->urb);
+err_hid_hw_stop:
+	hid_hw_stop(hdev);
+	return ret;
+}
+
+static void u2fzero_remove(struct hid_device *hdev)
+{
+	struct u2fzero_device *dev = hid_get_drvdata(hdev);
+
+	mutex_lock(&dev->lock);
+	dev->present = false;
+	mutex_unlock(&dev->lock);
+
+	hid_hw_stop(hdev);
+	usb_poison_urb(dev->urb);
+	usb_free_urb(dev->urb);
+}
+
+static const struct hid_device_id u2fzero_table[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_CYGNAL,
+	  USB_DEVICE_ID_U2F_ZERO),
+	  .driver_data = HW_U2FZERO },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_CLAY_LOGIC,
+	  USB_DEVICE_ID_NITROKEY_U2F),
+	  .driver_data = HW_NITROKEY_U2F },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, u2fzero_table);
+
+static struct hid_driver u2fzero_driver = {
+	.name = "hid-" DRIVER_SHORT,
+	.probe = u2fzero_probe,
+	.remove = u2fzero_remove,
+	.id_table = u2fzero_table,
+};
+
+module_hid_driver(u2fzero_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Andrej Shadura <andrew@shadura.me>");
+MODULE_DESCRIPTION("U2F Zero LED and RNG driver");