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, 154 insertions, 0 deletions

diff --git a/security/selinux/genheaders.c b/security/selinux/genheaders.c
new file mode 100644
index 000000000..3834d7eb0
--- /dev/null
+++ b/security/selinux/genheaders.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+
+struct security_class_mapping {
+	const char *name;
+	const char *perms[sizeof(unsigned) * 8 + 1];
+};
+
+#include "classmap.h"
+#include "initial_sid_to_string.h"
+
+const char *progname;
+
+static void usage(void)
+{
+	printf("usage: %s flask.h av_permissions.h\n", progname);
+	exit(1);
+}
+
+static char *stoupperx(const char *s)
+{
+	char *s2 = strdup(s);
+	char *p;
+
+	if (!s2) {
+		fprintf(stderr, "%s:  out of memory\n", progname);
+		exit(3);
+	}
+
+	for (p = s2; *p; p++)
+		*p = toupper(*p);
+	return s2;
+}
+
+int main(int argc, char *argv[])
+{
+	int i, j;
+	int isids_len;
+	FILE *fout;
+
+	progname = argv[0];
+
+	if (argc < 3)
+		usage();
+
+	fout = fopen(argv[1], "w");
+	if (!fout) {
+		fprintf(stderr, "Could not open %s for writing:  %s\n",
+			argv[1], strerror(errno));
+		exit(2);
+	}
+
+	fprintf(fout, "/* This file is automatically generated.  Do not edit. */\n");
+	fprintf(fout, "#ifndef _SELINUX_FLASK_H_\n#define _SELINUX_FLASK_H_\n\n");
+
+	for (i = 0; secclass_map[i].name; i++) {
+		char *name = stoupperx(secclass_map[i].name);
+
+		fprintf(fout, "#define SECCLASS_%-39s %2d\n", name, i+1);
+		free(name);
+	}
+
+	fprintf(fout, "\n");
+
+	isids_len = sizeof(initial_sid_to_string) / sizeof(char *);
+	for (i = 1; i < isids_len; i++) {
+		const char *s = initial_sid_to_string[i];
+		if (s) {
+			char *sidname = stoupperx(s);
+
+			fprintf(fout, "#define SECINITSID_%-39s %2d\n", sidname, i);
+			free(sidname);
+		}
+	}
+	fprintf(fout, "\n#define SECINITSID_NUM %d\n", i-1);
+	fprintf(fout, "\nstatic inline bool security_is_socket_class(u16 kern_tclass)\n");
+	fprintf(fout, "{\n");
+	fprintf(fout, "\tbool sock = false;\n\n");
+	fprintf(fout, "\tswitch (kern_tclass) {\n");
+	for (i = 0; secclass_map[i].name; i++) {
+		static char s[] = "SOCKET";
+		int len, l;
+		char *name = stoupperx(secclass_map[i].name);
+
+		len = strlen(name);
+		l = sizeof(s) - 1;
+		if (len >= l && memcmp(name + len - l, s, l) == 0)
+			fprintf(fout, "\tcase SECCLASS_%s:\n", name);
+		free(name);
+	}
+	fprintf(fout, "\t\tsock = true;\n");
+	fprintf(fout, "\t\tbreak;\n");
+	fprintf(fout, "\tdefault:\n");
+	fprintf(fout, "\t\tbreak;\n");
+	fprintf(fout, "\t}\n\n");
+	fprintf(fout, "\treturn sock;\n");
+	fprintf(fout, "}\n");
+
+	fprintf(fout, "\n#endif\n");
+
+	if (fclose(fout) != 0) {
+		fprintf(stderr, "Could not successfully close %s:  %s\n",
+			argv[1], strerror(errno));
+		exit(4);
+	}
+
+	fout = fopen(argv[2], "w");
+	if (!fout) {
+		fprintf(stderr, "Could not open %s for writing:  %s\n",
+			argv[2], strerror(errno));
+		exit(5);
+	}
+
+	fprintf(fout, "/* This file is automatically generated.  Do not edit. */\n");
+	fprintf(fout, "#ifndef _SELINUX_AV_PERMISSIONS_H_\n#define _SELINUX_AV_PERMISSIONS_H_\n\n");
+
+	for (i = 0; secclass_map[i].name; i++) {
+		const struct security_class_mapping *map = &secclass_map[i];
+		int len;
+		char *name = stoupperx(map->name);
+
+		len = strlen(name);
+		for (j = 0; map->perms[j]; j++) {
+			char *permname;
+
+			if (j >= 32) {
+				fprintf(stderr, "Too many permissions to fit into an access vector at (%s, %s).\n",
+					map->name, map->perms[j]);
+				exit(5);
+			}
+			permname = stoupperx(map->perms[j]);
+			fprintf(fout, "#define %s__%-*s 0x%08xU\n", name,
+				39-len, permname, 1U<<j);
+			free(permname);
+		}
+		free(name);
+	}
+
+	fprintf(fout, "\n#endif\n");
+
+	if (fclose(fout) != 0) {
+		fprintf(stderr, "Could not successfully close %s:  %s\n",
+			argv[2], strerror(errno));
+		exit(6);
+	}
+
+	exit(0);
+}