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, 342 insertions, 0 deletions

diff --git a/drivers/firmware/efi/capsule-loader.c b/drivers/firmware/efi/capsule-loader.c
new file mode 100644
index 000000000..8e8f81f0a
--- /dev/null
+++ b/drivers/firmware/efi/capsule-loader.c
@@ -0,0 +1,342 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * EFI capsule loader driver.
+ *
+ * Copyright 2015 Intel Corporation
+ */
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/miscdevice.h>
+#include <linux/highmem.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <linux/efi.h>
+#include <linux/vmalloc.h>
+
+#define NO_FURTHER_WRITE_ACTION -1
+
+/**
+ * efi_free_all_buff_pages - free all previous allocated buffer pages
+ * @cap_info: pointer to current instance of capsule_info structure
+ *
+ *	In addition to freeing buffer pages, it flags NO_FURTHER_WRITE_ACTION
+ *	to cease processing data in subsequent write(2) calls until close(2)
+ *	is called.
+ **/
+static void efi_free_all_buff_pages(struct capsule_info *cap_info)
+{
+	while (cap_info->index > 0)
+		__free_page(cap_info->pages[--cap_info->index]);
+
+	cap_info->index = NO_FURTHER_WRITE_ACTION;
+}
+
+int __efi_capsule_setup_info(struct capsule_info *cap_info)
+{
+	size_t pages_needed;
+	int ret;
+	void *temp_page;
+
+	pages_needed = ALIGN(cap_info->total_size, PAGE_SIZE) / PAGE_SIZE;
+
+	if (pages_needed == 0) {
+		pr_err("invalid capsule size\n");
+		return -EINVAL;
+	}
+
+	/* Check if the capsule binary supported */
+	ret = efi_capsule_supported(cap_info->header.guid,
+				    cap_info->header.flags,
+				    cap_info->header.imagesize,
+				    &cap_info->reset_type);
+	if (ret) {
+		pr_err("capsule not supported\n");
+		return ret;
+	}
+
+	temp_page = krealloc(cap_info->pages,
+			     pages_needed * sizeof(void *),
+			     GFP_KERNEL | __GFP_ZERO);
+	if (!temp_page)
+		return -ENOMEM;
+
+	cap_info->pages = temp_page;
+
+	temp_page = krealloc(cap_info->phys,
+			     pages_needed * sizeof(phys_addr_t),
+			     GFP_KERNEL | __GFP_ZERO);
+	if (!temp_page)
+		return -ENOMEM;
+
+	cap_info->phys = temp_page;
+
+	return 0;
+}
+
+/**
+ * efi_capsule_setup_info - obtain the efi capsule header in the binary and
+ *			    setup capsule_info structure
+ * @cap_info: pointer to current instance of capsule_info structure
+ * @kbuff: a mapped first page buffer pointer
+ * @hdr_bytes: the total received number of bytes for efi header
+ *
+ * Platforms with non-standard capsule update mechanisms can override
+ * this __weak function so they can perform any required capsule
+ * image munging. See quark_quirk_function() for an example.
+ **/
+int __weak efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
+				  size_t hdr_bytes)
+{
+	/* Only process data block that is larger than efi header size */
+	if (hdr_bytes < sizeof(efi_capsule_header_t))
+		return 0;
+
+	memcpy(&cap_info->header, kbuff, sizeof(cap_info->header));
+	cap_info->total_size = cap_info->header.imagesize;
+
+	return __efi_capsule_setup_info(cap_info);
+}
+
+/**
+ * efi_capsule_submit_update - invoke the efi_capsule_update API once binary
+ *			       upload done
+ * @cap_info: pointer to current instance of capsule_info structure
+ **/
+static ssize_t efi_capsule_submit_update(struct capsule_info *cap_info)
+{
+	bool do_vunmap = false;
+	int ret;
+
+	/*
+	 * cap_info->capsule may have been assigned already by a quirk
+	 * handler, so only overwrite it if it is NULL
+	 */
+	if (!cap_info->capsule) {
+		cap_info->capsule = vmap(cap_info->pages, cap_info->index,
+					 VM_MAP, PAGE_KERNEL);
+		if (!cap_info->capsule)
+			return -ENOMEM;
+		do_vunmap = true;
+	}
+
+	ret = efi_capsule_update(cap_info->capsule, cap_info->phys);
+	if (do_vunmap)
+		vunmap(cap_info->capsule);
+	if (ret) {
+		pr_err("capsule update failed\n");
+		return ret;
+	}
+
+	/* Indicate capsule binary uploading is done */
+	cap_info->index = NO_FURTHER_WRITE_ACTION;
+
+	if (cap_info->header.flags & EFI_CAPSULE_PERSIST_ACROSS_RESET) {
+		pr_info("Successfully uploaded capsule file with reboot type '%s'\n",
+			!cap_info->reset_type ? "RESET_COLD" :
+			cap_info->reset_type == 1 ? "RESET_WARM" :
+			"RESET_SHUTDOWN");
+	} else {
+		pr_info("Successfully processed capsule file\n");
+	}
+
+	return 0;
+}
+
+/**
+ * efi_capsule_write - store the capsule binary and pass it to
+ *		       efi_capsule_update() API
+ * @file: file pointer
+ * @buff: buffer pointer
+ * @count: number of bytes in @buff
+ * @offp: not used
+ *
+ *	Expectation:
+ *	- A user space tool should start at the beginning of capsule binary and
+ *	  pass data in sequentially.
+ *	- Users should close and re-open this file note in order to upload more
+ *	  capsules.
+ *	- After an error returned, user should close the file and restart the
+ *	  operation for the next try otherwise -EIO will be returned until the
+ *	  file is closed.
+ *	- An EFI capsule header must be located at the beginning of capsule
+ *	  binary file and passed in as first block data of write operation.
+ **/
+static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
+				 size_t count, loff_t *offp)
+{
+	int ret;
+	struct capsule_info *cap_info = file->private_data;
+	struct page *page;
+	void *kbuff = NULL;
+	size_t write_byte;
+
+	if (count == 0)
+		return 0;
+
+	/* Return error while NO_FURTHER_WRITE_ACTION is flagged */
+	if (cap_info->index < 0)
+		return -EIO;
+
+	/* Only alloc a new page when previous page is full */
+	if (!cap_info->page_bytes_remain) {
+		page = alloc_page(GFP_KERNEL);
+		if (!page) {
+			ret = -ENOMEM;
+			goto failed;
+		}
+
+		cap_info->pages[cap_info->index] = page;
+		cap_info->phys[cap_info->index] = page_to_phys(page);
+		cap_info->page_bytes_remain = PAGE_SIZE;
+		cap_info->index++;
+	} else {
+		page = cap_info->pages[cap_info->index - 1];
+	}
+
+	kbuff = kmap(page);
+	kbuff += PAGE_SIZE - cap_info->page_bytes_remain;
+
+	/* Copy capsule binary data from user space to kernel space buffer */
+	write_byte = min_t(size_t, count, cap_info->page_bytes_remain);
+	if (copy_from_user(kbuff, buff, write_byte)) {
+		ret = -EFAULT;
+		goto fail_unmap;
+	}
+	cap_info->page_bytes_remain -= write_byte;
+
+	/* Setup capsule binary info structure */
+	if (cap_info->header.headersize == 0) {
+		ret = efi_capsule_setup_info(cap_info, kbuff - cap_info->count,
+					     cap_info->count + write_byte);
+		if (ret)
+			goto fail_unmap;
+	}
+
+	cap_info->count += write_byte;
+	kunmap(page);
+
+	/* Submit the full binary to efi_capsule_update() API */
+	if (cap_info->header.headersize > 0 &&
+	    cap_info->count >= cap_info->total_size) {
+		if (cap_info->count > cap_info->total_size) {
+			pr_err("capsule upload size exceeded header defined size\n");
+			ret = -EINVAL;
+			goto failed;
+		}
+
+		ret = efi_capsule_submit_update(cap_info);
+		if (ret)
+			goto failed;
+	}
+
+	return write_byte;
+
+fail_unmap:
+	kunmap(page);
+failed:
+	efi_free_all_buff_pages(cap_info);
+	return ret;
+}
+
+/**
+ * efi_capsule_release - called by file close
+ * @inode: not used
+ * @file: file pointer
+ *
+ *	We will not free successfully submitted pages since efi update
+ *	requires data to be maintained across system reboot.
+ **/
+static int efi_capsule_release(struct inode *inode, struct file *file)
+{
+	struct capsule_info *cap_info = file->private_data;
+
+	if (cap_info->index > 0 &&
+	    (cap_info->header.headersize == 0 ||
+	     cap_info->count < cap_info->total_size)) {
+		pr_err("capsule upload not complete\n");
+		efi_free_all_buff_pages(cap_info);
+	}
+
+	kfree(cap_info->pages);
+	kfree(cap_info->phys);
+	kfree(file->private_data);
+	file->private_data = NULL;
+	return 0;
+}
+
+/**
+ * efi_capsule_open - called by file open
+ * @inode: not used
+ * @file: file pointer
+ *
+ *	Will allocate each capsule_info memory for each file open call.
+ *	This provided the capability to support multiple file open feature
+ *	where user is not needed to wait for others to finish in order to
+ *	upload their capsule binary.
+ **/
+static int efi_capsule_open(struct inode *inode, struct file *file)
+{
+	struct capsule_info *cap_info;
+
+	cap_info = kzalloc_obj(*cap_info);
+	if (!cap_info)
+		return -ENOMEM;
+
+	cap_info->pages = kzalloc(sizeof(void *), GFP_KERNEL);
+	if (!cap_info->pages) {
+		kfree(cap_info);
+		return -ENOMEM;
+	}
+
+	cap_info->phys = kzalloc_obj(phys_addr_t);
+	if (!cap_info->phys) {
+		kfree(cap_info->pages);
+		kfree(cap_info);
+		return -ENOMEM;
+	}
+
+	file->private_data = cap_info;
+
+	return 0;
+}
+
+static const struct file_operations efi_capsule_fops = {
+	.owner = THIS_MODULE,
+	.open = efi_capsule_open,
+	.write = efi_capsule_write,
+	.release = efi_capsule_release,
+};
+
+static struct miscdevice efi_capsule_misc = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "efi_capsule_loader",
+	.fops = &efi_capsule_fops,
+};
+
+static int __init efi_capsule_loader_init(void)
+{
+	int ret;
+
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return -ENODEV;
+
+	ret = misc_register(&efi_capsule_misc);
+	if (ret)
+		pr_err("Unable to register capsule loader device\n");
+
+	return ret;
+}
+module_init(efi_capsule_loader_init);
+
+static void __exit efi_capsule_loader_exit(void)
+{
+	misc_deregister(&efi_capsule_misc);
+}
+module_exit(efi_capsule_loader_exit);
+
+MODULE_DESCRIPTION("EFI capsule firmware binary loader");
+MODULE_LICENSE("GPL v2");