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, 259 insertions, 0 deletions

diff --git a/drivers/crypto/ccp/dbc.c b/drivers/crypto/ccp/dbc.c
new file mode 100644
index 000000000..410084a90
--- /dev/null
+++ b/drivers/crypto/ccp/dbc.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AMD Secure Processor Dynamic Boost Control interface
+ *
+ * Copyright (C) 2023 Advanced Micro Devices, Inc.
+ *
+ * Author: Mario Limonciello <mario.limonciello@amd.com>
+ */
+
+#include <linux/mutex.h>
+
+#include "dbc.h"
+
+#define DBC_DEFAULT_TIMEOUT		(10 * MSEC_PER_SEC)
+struct error_map {
+	u32 psp;
+	int ret;
+};
+
+#define DBC_ERROR_ACCESS_DENIED		0x0001
+#define DBC_ERROR_EXCESS_DATA		0x0004
+#define DBC_ERROR_BAD_PARAMETERS	0x0006
+#define DBC_ERROR_BAD_STATE		0x0007
+#define DBC_ERROR_NOT_IMPLEMENTED	0x0009
+#define DBC_ERROR_BUSY			0x000D
+#define DBC_ERROR_MESSAGE_FAILURE	0x0307
+#define DBC_ERROR_OVERFLOW		0x300F
+#define DBC_ERROR_SIGNATURE_INVALID	0x3072
+
+static struct error_map error_codes[] = {
+	{DBC_ERROR_ACCESS_DENIED,	-EACCES},
+	{DBC_ERROR_EXCESS_DATA,		-E2BIG},
+	{DBC_ERROR_BAD_PARAMETERS,	-EINVAL},
+	{DBC_ERROR_BAD_STATE,		-EAGAIN},
+	{DBC_ERROR_MESSAGE_FAILURE,	-ENOENT},
+	{DBC_ERROR_NOT_IMPLEMENTED,	-ENOENT},
+	{DBC_ERROR_BUSY,		-EBUSY},
+	{DBC_ERROR_OVERFLOW,		-ENFILE},
+	{DBC_ERROR_SIGNATURE_INVALID,	-EPERM},
+	{0x0,	0x0},
+};
+
+static inline int send_dbc_cmd_thru_ext(struct psp_dbc_device *dbc_dev, int msg)
+{
+	dbc_dev->mbox->ext_req.header.sub_cmd_id = msg;
+
+	return psp_extended_mailbox_cmd(dbc_dev->psp,
+					DBC_DEFAULT_TIMEOUT,
+					(struct psp_ext_request *)dbc_dev->mbox);
+}
+
+static inline int send_dbc_cmd_thru_pa(struct psp_dbc_device *dbc_dev, int msg)
+{
+	return psp_send_platform_access_msg(msg,
+					    (struct psp_request *)dbc_dev->mbox);
+}
+
+static int send_dbc_cmd(struct psp_dbc_device *dbc_dev, int msg)
+{
+	int ret;
+
+	*dbc_dev->result = 0;
+	ret = dbc_dev->use_ext ? send_dbc_cmd_thru_ext(dbc_dev, msg) :
+				 send_dbc_cmd_thru_pa(dbc_dev, msg);
+	if (ret == -EIO) {
+		int i;
+
+		dev_dbg(dbc_dev->dev,
+			 "msg 0x%x failed with PSP error: 0x%x\n",
+			 msg, *dbc_dev->result);
+
+		for (i = 0; error_codes[i].psp; i++) {
+			if (*dbc_dev->result == error_codes[i].psp)
+				return error_codes[i].ret;
+		}
+	}
+
+	return ret;
+}
+
+static int send_dbc_nonce(struct psp_dbc_device *dbc_dev)
+{
+	int ret;
+
+	*dbc_dev->payload_size = dbc_dev->header_size + sizeof(struct dbc_user_nonce);
+	ret = send_dbc_cmd(dbc_dev, PSP_DYNAMIC_BOOST_GET_NONCE);
+	if (ret == -EAGAIN) {
+		dev_dbg(dbc_dev->dev, "retrying get nonce\n");
+		ret = send_dbc_cmd(dbc_dev, PSP_DYNAMIC_BOOST_GET_NONCE);
+	}
+
+	return ret;
+}
+
+static int send_dbc_parameter(struct psp_dbc_device *dbc_dev)
+{
+	struct dbc_user_param *user_param = (struct dbc_user_param *)dbc_dev->payload;
+
+	switch (user_param->msg_index) {
+	case PARAM_SET_FMAX_CAP:
+	case PARAM_SET_PWR_CAP:
+	case PARAM_SET_GFX_MODE:
+		return send_dbc_cmd(dbc_dev, PSP_DYNAMIC_BOOST_SET_PARAMETER);
+	case PARAM_GET_FMAX_CAP:
+	case PARAM_GET_PWR_CAP:
+	case PARAM_GET_CURR_TEMP:
+	case PARAM_GET_FMAX_MAX:
+	case PARAM_GET_FMAX_MIN:
+	case PARAM_GET_SOC_PWR_MAX:
+	case PARAM_GET_SOC_PWR_MIN:
+	case PARAM_GET_SOC_PWR_CUR:
+	case PARAM_GET_GFX_MODE:
+		return send_dbc_cmd(dbc_dev, PSP_DYNAMIC_BOOST_GET_PARAMETER);
+	}
+
+	return -EINVAL;
+}
+
+void dbc_dev_destroy(struct psp_device *psp)
+{
+	struct psp_dbc_device *dbc_dev = psp->dbc_data;
+
+	if (!dbc_dev)
+		return;
+
+	misc_deregister(&dbc_dev->char_dev);
+	mutex_destroy(&dbc_dev->ioctl_mutex);
+	psp->dbc_data = NULL;
+}
+
+static long dbc_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	struct psp_device *psp_master = psp_get_master_device();
+	void __user *argp = (void __user *)arg;
+	struct psp_dbc_device *dbc_dev;
+	int ret;
+
+	if (!psp_master || !psp_master->dbc_data)
+		return -ENODEV;
+	dbc_dev = psp_master->dbc_data;
+
+	guard(mutex)(&dbc_dev->ioctl_mutex);
+
+	switch (cmd) {
+	case DBCIOCNONCE:
+		if (copy_from_user(dbc_dev->payload, argp, sizeof(struct dbc_user_nonce)))
+			return -EFAULT;
+
+		ret = send_dbc_nonce(dbc_dev);
+		if (ret)
+			return ret;
+
+		if (copy_to_user(argp, dbc_dev->payload, sizeof(struct dbc_user_nonce)))
+			return -EFAULT;
+		break;
+	case DBCIOCUID:
+		if (copy_from_user(dbc_dev->payload, argp, sizeof(struct dbc_user_setuid)))
+			return -EFAULT;
+
+		*dbc_dev->payload_size = dbc_dev->header_size + sizeof(struct dbc_user_setuid);
+		ret = send_dbc_cmd(dbc_dev, PSP_DYNAMIC_BOOST_SET_UID);
+		if (ret)
+			return ret;
+
+		if (copy_to_user(argp, dbc_dev->payload, sizeof(struct dbc_user_setuid)))
+			return -EFAULT;
+		break;
+	case DBCIOCPARAM:
+		if (copy_from_user(dbc_dev->payload, argp, sizeof(struct dbc_user_param)))
+			return -EFAULT;
+
+		*dbc_dev->payload_size = dbc_dev->header_size + sizeof(struct dbc_user_param);
+		ret = send_dbc_parameter(dbc_dev);
+		if (ret)
+			return ret;
+
+		if (copy_to_user(argp, dbc_dev->payload, sizeof(struct dbc_user_param)))
+			return -EFAULT;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct file_operations dbc_fops = {
+	.owner	= THIS_MODULE,
+	.unlocked_ioctl = dbc_ioctl,
+};
+
+int dbc_dev_init(struct psp_device *psp)
+{
+	struct device *dev = psp->dev;
+	struct psp_dbc_device *dbc_dev;
+	int ret;
+
+	dbc_dev = devm_kzalloc(dev, sizeof(*dbc_dev), GFP_KERNEL);
+	if (!dbc_dev)
+		return -ENOMEM;
+
+	BUILD_BUG_ON(sizeof(union dbc_buffer) > PAGE_SIZE);
+	dbc_dev->mbox = (void *)devm_get_free_pages(dev, GFP_KERNEL | __GFP_ZERO, 0);
+	if (!dbc_dev->mbox) {
+		ret = -ENOMEM;
+		goto cleanup_dev;
+	}
+
+	psp->dbc_data = dbc_dev;
+	dbc_dev->dev = dev;
+	dbc_dev->psp = psp;
+
+	if (psp->capability.dbc_thru_ext) {
+		dbc_dev->use_ext = true;
+		dbc_dev->payload_size = &dbc_dev->mbox->ext_req.header.payload_size;
+		dbc_dev->result = &dbc_dev->mbox->ext_req.header.status;
+		dbc_dev->payload = &dbc_dev->mbox->ext_req.buf;
+		dbc_dev->header_size = sizeof(struct psp_ext_req_buffer_hdr);
+	} else {
+		dbc_dev->payload_size = &dbc_dev->mbox->pa_req.header.payload_size;
+		dbc_dev->result = &dbc_dev->mbox->pa_req.header.status;
+		dbc_dev->payload = &dbc_dev->mbox->pa_req.buf;
+		dbc_dev->header_size = sizeof(struct psp_req_buffer_hdr);
+	}
+
+	ret = send_dbc_nonce(dbc_dev);
+	if (ret == -EACCES) {
+		dev_dbg(dbc_dev->dev,
+			"dynamic boost control was previously authenticated\n");
+		ret = 0;
+	}
+	dev_dbg(dbc_dev->dev, "dynamic boost control is %savailable\n",
+		ret ? "un" : "");
+	if (ret) {
+		ret = 0;
+		goto cleanup_mbox;
+	}
+
+	dbc_dev->char_dev.minor = MISC_DYNAMIC_MINOR;
+	dbc_dev->char_dev.name = "dbc";
+	dbc_dev->char_dev.fops = &dbc_fops;
+	dbc_dev->char_dev.mode = 0600;
+	ret = misc_register(&dbc_dev->char_dev);
+	if (ret)
+		goto cleanup_mbox;
+
+	mutex_init(&dbc_dev->ioctl_mutex);
+
+	return 0;
+
+cleanup_mbox:
+	devm_free_pages(dev, (unsigned long)dbc_dev->mbox);
+
+cleanup_dev:
+	psp->dbc_data = NULL;
+	devm_kfree(dev, dbc_dev);
+
+	return ret;
+}