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, 242 insertions, 0 deletions

diff --git a/security/tomoyo/mount.c b/security/tomoyo/mount.c
new file mode 100644
index 000000000..322dfd188
--- /dev/null
+++ b/security/tomoyo/mount.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * security/tomoyo/mount.c
+ *
+ * Copyright (C) 2005-2011  NTT DATA CORPORATION
+ */
+
+#include <linux/slab.h>
+#include <uapi/linux/mount.h>
+#include "common.h"
+
+/* String table for special mount operations. */
+static const char * const tomoyo_mounts[TOMOYO_MAX_SPECIAL_MOUNT] = {
+	[TOMOYO_MOUNT_BIND]            = "--bind",
+	[TOMOYO_MOUNT_MOVE]            = "--move",
+	[TOMOYO_MOUNT_REMOUNT]         = "--remount",
+	[TOMOYO_MOUNT_MAKE_UNBINDABLE] = "--make-unbindable",
+	[TOMOYO_MOUNT_MAKE_PRIVATE]    = "--make-private",
+	[TOMOYO_MOUNT_MAKE_SLAVE]      = "--make-slave",
+	[TOMOYO_MOUNT_MAKE_SHARED]     = "--make-shared",
+};
+
+/**
+ * tomoyo_audit_mount_log - Audit mount log.
+ *
+ * @r: Pointer to "struct tomoyo_request_info".
+ *
+ * Returns 0 on success, negative value otherwise.
+ */
+static int tomoyo_audit_mount_log(struct tomoyo_request_info *r)
+	__must_hold_shared(&tomoyo_ss)
+{
+	return tomoyo_supervisor(r, "file mount %s %s %s 0x%lX\n",
+				 r->param.mount.dev->name,
+				 r->param.mount.dir->name,
+				 r->param.mount.type->name,
+				 r->param.mount.flags);
+}
+
+/**
+ * tomoyo_check_mount_acl - Check permission for path path path number operation.
+ *
+ * @r:   Pointer to "struct tomoyo_request_info".
+ * @ptr: Pointer to "struct tomoyo_acl_info".
+ *
+ * Returns true if granted, false otherwise.
+ */
+static bool tomoyo_check_mount_acl(struct tomoyo_request_info *r,
+				   const struct tomoyo_acl_info *ptr)
+{
+	const struct tomoyo_mount_acl *acl =
+		container_of(ptr, typeof(*acl), head);
+
+	return tomoyo_compare_number_union(r->param.mount.flags,
+					   &acl->flags) &&
+		tomoyo_compare_name_union(r->param.mount.type,
+					  &acl->fs_type) &&
+		tomoyo_compare_name_union(r->param.mount.dir,
+					  &acl->dir_name) &&
+		(!r->param.mount.need_dev ||
+		 tomoyo_compare_name_union(r->param.mount.dev,
+					   &acl->dev_name));
+}
+
+/**
+ * tomoyo_mount_acl - Check permission for mount() operation.
+ *
+ * @r:        Pointer to "struct tomoyo_request_info".
+ * @dev_name: Name of device file. Maybe NULL.
+ * @dir:      Pointer to "struct path".
+ * @type:     Name of filesystem type.
+ * @flags:    Mount options.
+ *
+ * Returns 0 on success, negative value otherwise.
+ *
+ * Caller holds tomoyo_read_lock().
+ */
+static int tomoyo_mount_acl(struct tomoyo_request_info *r,
+			    const char *dev_name,
+			    const struct path *dir, const char *type,
+			    unsigned long flags)
+	__must_hold_shared(&tomoyo_ss)
+{
+	struct tomoyo_obj_info obj = { };
+	struct path path;
+	struct file_system_type *fstype = NULL;
+	const char *requested_type = NULL;
+	const char *requested_dir_name = NULL;
+	const char *requested_dev_name = NULL;
+	struct tomoyo_path_info rtype;
+	struct tomoyo_path_info rdev;
+	struct tomoyo_path_info rdir;
+	int need_dev = 0;
+	int error = -ENOMEM;
+
+	r->obj = &obj;
+
+	/* Get fstype. */
+	requested_type = tomoyo_encode(type);
+	if (!requested_type)
+		goto out;
+	rtype.name = requested_type;
+	tomoyo_fill_path_info(&rtype);
+
+	/* Get mount point. */
+	obj.path2 = *dir;
+	requested_dir_name = tomoyo_realpath_from_path(dir);
+	if (!requested_dir_name) {
+		error = -ENOMEM;
+		goto out;
+	}
+	rdir.name = requested_dir_name;
+	tomoyo_fill_path_info(&rdir);
+
+	/* Compare fs name. */
+	if (type == tomoyo_mounts[TOMOYO_MOUNT_REMOUNT]) {
+		/* dev_name is ignored. */
+	} else if (type == tomoyo_mounts[TOMOYO_MOUNT_MAKE_UNBINDABLE] ||
+		   type == tomoyo_mounts[TOMOYO_MOUNT_MAKE_PRIVATE] ||
+		   type == tomoyo_mounts[TOMOYO_MOUNT_MAKE_SLAVE] ||
+		   type == tomoyo_mounts[TOMOYO_MOUNT_MAKE_SHARED]) {
+		/* dev_name is ignored. */
+	} else if (type == tomoyo_mounts[TOMOYO_MOUNT_BIND] ||
+		   type == tomoyo_mounts[TOMOYO_MOUNT_MOVE]) {
+		need_dev = -1; /* dev_name is a directory */
+	} else {
+		fstype = get_fs_type(type);
+		if (!fstype) {
+			error = -ENODEV;
+			goto out;
+		}
+		if (fstype->fs_flags & FS_REQUIRES_DEV)
+			/* dev_name is a block device file. */
+			need_dev = 1;
+	}
+	if (need_dev) {
+		/* Get mount point or device file. */
+		if (!dev_name || kern_path(dev_name, LOOKUP_FOLLOW, &path)) {
+			error = -ENOENT;
+			goto out;
+		}
+		obj.path1 = path;
+		requested_dev_name = tomoyo_realpath_from_path(&path);
+		if (!requested_dev_name) {
+			error = -ENOENT;
+			goto out;
+		}
+	} else {
+		/* Map dev_name to "<NULL>" if no dev_name given. */
+		if (!dev_name)
+			dev_name = "<NULL>";
+		requested_dev_name = tomoyo_encode(dev_name);
+		if (!requested_dev_name) {
+			error = -ENOMEM;
+			goto out;
+		}
+	}
+	rdev.name = requested_dev_name;
+	tomoyo_fill_path_info(&rdev);
+	r->param_type = TOMOYO_TYPE_MOUNT_ACL;
+	r->param.mount.need_dev = need_dev;
+	r->param.mount.dev = &rdev;
+	r->param.mount.dir = &rdir;
+	r->param.mount.type = &rtype;
+	r->param.mount.flags = flags;
+	do {
+		tomoyo_check_acl(r, tomoyo_check_mount_acl);
+		error = tomoyo_audit_mount_log(r);
+	} while (error == TOMOYO_RETRY_REQUEST);
+ out:
+	kfree(requested_dev_name);
+	kfree(requested_dir_name);
+	if (fstype)
+		put_filesystem(fstype);
+	kfree(requested_type);
+	/* Drop refcount obtained by kern_path(). */
+	if (obj.path1.dentry)
+		path_put(&obj.path1);
+	return error;
+}
+
+/**
+ * tomoyo_mount_permission - Check permission for mount() operation.
+ *
+ * @dev_name:  Name of device file. Maybe NULL.
+ * @path:      Pointer to "struct path".
+ * @type:      Name of filesystem type. Maybe NULL.
+ * @flags:     Mount options.
+ * @data_page: Optional data. Maybe NULL.
+ *
+ * Returns 0 on success, negative value otherwise.
+ */
+int tomoyo_mount_permission(const char *dev_name, const struct path *path,
+			    const char *type, unsigned long flags,
+			    void *data_page)
+{
+	struct tomoyo_request_info r;
+	int error;
+	int idx;
+
+	if (tomoyo_init_request_info(&r, NULL, TOMOYO_MAC_FILE_MOUNT)
+	    == TOMOYO_CONFIG_DISABLED)
+		return 0;
+	if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
+		flags &= ~MS_MGC_MSK;
+	if (flags & MS_REMOUNT) {
+		type = tomoyo_mounts[TOMOYO_MOUNT_REMOUNT];
+		flags &= ~MS_REMOUNT;
+	} else if (flags & MS_BIND) {
+		type = tomoyo_mounts[TOMOYO_MOUNT_BIND];
+		flags &= ~MS_BIND;
+	} else if (flags & MS_SHARED) {
+		if (flags & (MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
+			return -EINVAL;
+		type = tomoyo_mounts[TOMOYO_MOUNT_MAKE_SHARED];
+		flags &= ~MS_SHARED;
+	} else if (flags & MS_PRIVATE) {
+		if (flags & (MS_SHARED | MS_SLAVE | MS_UNBINDABLE))
+			return -EINVAL;
+		type = tomoyo_mounts[TOMOYO_MOUNT_MAKE_PRIVATE];
+		flags &= ~MS_PRIVATE;
+	} else if (flags & MS_SLAVE) {
+		if (flags & (MS_SHARED | MS_PRIVATE | MS_UNBINDABLE))
+			return -EINVAL;
+		type = tomoyo_mounts[TOMOYO_MOUNT_MAKE_SLAVE];
+		flags &= ~MS_SLAVE;
+	} else if (flags & MS_UNBINDABLE) {
+		if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE))
+			return -EINVAL;
+		type = tomoyo_mounts[TOMOYO_MOUNT_MAKE_UNBINDABLE];
+		flags &= ~MS_UNBINDABLE;
+	} else if (flags & MS_MOVE) {
+		type = tomoyo_mounts[TOMOYO_MOUNT_MOVE];
+		flags &= ~MS_MOVE;
+	}
+	if (!type)
+		type = "<NULL>";
+	idx = tomoyo_read_lock();
+	error = tomoyo_mount_acl(&r, dev_name, path, type, flags);
+	tomoyo_read_unlock(idx);
+	return error;
+}