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, 161 insertions, 0 deletions

diff --git a/fs/fuse/acl.c b/fs/fuse/acl.c
new file mode 100644
index 000000000..31fb50e16
--- /dev/null
+++ b/fs/fuse/acl.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FUSE: Filesystem in Userspace
+ * Copyright (C) 2016 Canonical Ltd. <seth.forshee@canonical.com>
+ */
+
+#include "fuse_i.h"
+
+#include <linux/posix_acl.h>
+#include <linux/posix_acl_xattr.h>
+
+static struct posix_acl *__fuse_get_acl(struct fuse_conn *fc,
+					struct inode *inode, int type, bool rcu)
+{
+	int size;
+	const char *name;
+	void *value = NULL;
+	struct posix_acl *acl;
+
+	if (rcu)
+		return ERR_PTR(-ECHILD);
+
+	if (fuse_is_bad(inode))
+		return ERR_PTR(-EIO);
+
+	if (fc->no_getxattr)
+		return NULL;
+
+	if (type == ACL_TYPE_ACCESS)
+		name = XATTR_NAME_POSIX_ACL_ACCESS;
+	else if (type == ACL_TYPE_DEFAULT)
+		name = XATTR_NAME_POSIX_ACL_DEFAULT;
+	else
+		return ERR_PTR(-EOPNOTSUPP);
+
+	value = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!value)
+		return ERR_PTR(-ENOMEM);
+	size = fuse_getxattr(inode, name, value, PAGE_SIZE);
+	if (size > 0)
+		acl = posix_acl_from_xattr(fc->user_ns, value, size);
+	else if ((size == 0) || (size == -ENODATA) ||
+		 (size == -EOPNOTSUPP && fc->no_getxattr))
+		acl = NULL;
+	else if (size == -ERANGE)
+		acl = ERR_PTR(-E2BIG);
+	else
+		acl = ERR_PTR(size);
+
+	kfree(value);
+	return acl;
+}
+
+static inline bool fuse_no_acl(const struct fuse_conn *fc,
+			       const struct inode *inode)
+{
+	/*
+	 * Refuse interacting with POSIX ACLs for daemons that
+	 * don't support FUSE_POSIX_ACL and are not mounted on
+	 * the host to retain backwards compatibility.
+	 */
+	return !fc->posix_acl && (i_user_ns(inode) != &init_user_ns);
+}
+
+struct posix_acl *fuse_get_acl(struct mnt_idmap *idmap,
+			       struct dentry *dentry, int type)
+{
+	struct inode *inode = d_inode(dentry);
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	if (fuse_no_acl(fc, inode))
+		return ERR_PTR(-EOPNOTSUPP);
+
+	return __fuse_get_acl(fc, inode, type, false);
+}
+
+struct posix_acl *fuse_get_inode_acl(struct inode *inode, int type, bool rcu)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	/*
+	 * FUSE daemons before FUSE_POSIX_ACL was introduced could get and set
+	 * POSIX ACLs without them being used for permission checking by the
+	 * vfs. Retain that behavior for backwards compatibility as there are
+	 * filesystems that do all permission checking for acls in the daemon
+	 * and not in the kernel.
+	 */
+	if (!fc->posix_acl)
+		return NULL;
+	return __fuse_get_acl(fc,  inode, type, rcu);
+}
+
+int fuse_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
+		 struct posix_acl *acl, int type)
+{
+	struct inode *inode = d_inode(dentry);
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	const char *name;
+	int ret;
+
+	if (fuse_is_bad(inode))
+		return -EIO;
+
+	if (fc->no_setxattr || fuse_no_acl(fc, inode))
+		return -EOPNOTSUPP;
+
+	if (type == ACL_TYPE_ACCESS)
+		name = XATTR_NAME_POSIX_ACL_ACCESS;
+	else if (type == ACL_TYPE_DEFAULT)
+		name = XATTR_NAME_POSIX_ACL_DEFAULT;
+	else
+		return -EINVAL;
+
+	if (acl) {
+		unsigned int extra_flags = 0;
+		/*
+		 * Fuse userspace is responsible for updating access
+		 * permissions in the inode, if needed. fuse_setxattr
+		 * invalidates the inode attributes, which will force
+		 * them to be refreshed the next time they are used,
+		 * and it also updates i_ctime.
+		 */
+		size_t size;
+		void *value;
+
+		value = posix_acl_to_xattr(fc->user_ns, acl, &size, GFP_KERNEL);
+		if (!value)
+			return -ENOMEM;
+
+		if (size > PAGE_SIZE) {
+			kfree(value);
+			return -E2BIG;
+		}
+
+		/*
+		 * Fuse daemons without FUSE_POSIX_ACL never changed the passed
+		 * through POSIX ACLs. Such daemons don't expect setgid bits to
+		 * be stripped.
+		 */
+		if (fc->posix_acl &&
+		    !in_group_or_capable(idmap, inode,
+					 i_gid_into_vfsgid(idmap, inode)))
+			extra_flags |= FUSE_SETXATTR_ACL_KILL_SGID;
+
+		ret = fuse_setxattr(inode, name, value, size, 0, extra_flags);
+		kfree(value);
+	} else {
+		ret = fuse_removexattr(inode, name);
+	}
+
+	if (fc->posix_acl) {
+		/*
+		 * Fuse daemons without FUSE_POSIX_ACL never cached POSIX ACLs
+		 * and didn't invalidate attributes. Retain that behavior.
+		 */
+		forget_all_cached_acls(inode);
+		fuse_invalidate_attr(inode);
+	}
+
+	return ret;
+}