linux-kernel - [tip: x86/core] objtool: Add --cfi to generate the .cfi

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Date:   Wed, 02 Nov 2022 09:20:01 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/core] objtool: Add --cfi to generate the .cfi_sites section

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     9a479f766be1dd777e12e3e57b6ee4c3028a40a5
Gitweb:        https://git.kernel.org/tip/9a479f766be1dd777e12e3e57b6ee4c3028a40a5
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 27 Oct 2022 11:28:13 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 01 Nov 2022 13:44:10 +01:00

objtool: Add --cfi to generate the .cfi_sites section

Add the location of all __cfi_##name symbols (as generated by kCFI) to
a section such that we might re-write things at kernel boot.

Notably; boot time re-hashing and FineIBT are the intended use of
this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20221027092842.568039454@infradead.org
---
 tools/objtool/builtin-check.c           |  1 +-
 tools/objtool/check.c                   | 69 ++++++++++++++++++++++++-
 tools/objtool/include/objtool/builtin.h |  1 +-
 3 files changed, 71 insertions(+)

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 95fcece..868e3e3 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -80,6 +80,7 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate frame pointer rules"),
 	OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
 	OPT_BOOLEAN('u', "uaccess", &opts.uaccess, "validate uaccess rules for SMAP"),
+	OPT_BOOLEAN(0  , "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
 	OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
 
 	OPT_GROUP("Options:"),
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 27f35f5..55066c4 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -861,6 +861,68 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 	return 0;
 }
 
+static int create_cfi_sections(struct objtool_file *file)
+{
+	struct section *sec, *s;
+	struct symbol *sym;
+	unsigned int *loc;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".cfi_sites");
+	if (sec) {
+		INIT_LIST_HEAD(&file->call_list);
+		WARN("file already has .cfi_sites section, skipping");
+		return 0;
+	}
+
+	idx = 0;
+	for_each_sec(file, s) {
+		if (!s->text)
+			continue;
+
+		list_for_each_entry(sym, &s->symbol_list, list) {
+			if (sym->type != STT_FUNC)
+				continue;
+
+			if (strncmp(sym->name, "__cfi_", 6))
+				continue;
+
+			idx++;
+		}
+	}
+
+	sec = elf_create_section(file->elf, ".cfi_sites", 0, sizeof(unsigned int), idx);
+	if (!sec)
+		return -1;
+
+	idx = 0;
+	for_each_sec(file, s) {
+		if (!s->text)
+			continue;
+
+		list_for_each_entry(sym, &s->symbol_list, list) {
+			if (sym->type != STT_FUNC)
+				continue;
+
+			if (strncmp(sym->name, "__cfi_", 6))
+				continue;
+
+			loc = (unsigned int *)sec->data->d_buf + idx;
+			memset(loc, 0, sizeof(unsigned int));
+
+			if (elf_add_reloc_to_insn(file->elf, sec,
+						  idx * sizeof(unsigned int),
+						  R_X86_64_PC32,
+						  s, sym->offset))
+				return -1;
+
+			idx++;
+		}
+	}
+
+	return 0;
+}
+
 static int create_mcount_loc_sections(struct objtool_file *file)
 {
 	struct section *sec;
@@ -4430,6 +4492,13 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
+	if (opts.cfi) {
+		ret = create_cfi_sections(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
+	}
+
 	if (opts.rethunk) {
 		ret = create_return_sites_sections(file);
 		if (ret < 0)
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index f341b62..c44ff39 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -27,6 +27,7 @@ struct opts {
 	bool static_call;
 	bool uaccess;
 	int prefix;
+	bool cfi;
 
 	/* options: */
 	bool backtrace;