linux-kernel - Re: [PATCH 1/3] objtool: Add --backup

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Message-ID: <YD4obT3aoXPWl7Ax@hirez.programming.kicks-ass.net>
Date:   Tue, 2 Mar 2021 12:58:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     jpoimboe@...hat.com, mbenes@...e.cz, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 1/3] objtool: Add --backup

On Fri, Feb 26, 2021 at 12:48:19PM +0100, Borislav Petkov wrote:
> Yah, as mentioned on IRC and let me paste it here too, you need to
> supply mode with O_CREAT:
> 
> 	d = open(name, O_CREAT|O_RDWR|O_TRUNC,S_IRUSR);
> 
> or so. Also you could add perror("open") to those error paths so that it
> can say why it failed creating the backup file.

Patch now reads like:

---
Subject: objtool: Add --backup
From: Peter Zijlstra <peterz@...radead.org>
Date: Fri Feb 26 10:59:59 CET 2021

Teach objtool to write backups files, such that it becomes easier to
see what objtool did to the object file.

Backup files will be ${name}bj, such that file.o becomes file.obj.

Suggested-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Borislav Petkov <bp@...e.de>
---
 tools/objtool/builtin-check.c           |    4 +-
 tools/objtool/include/objtool/builtin.h |    3 +
 tools/objtool/objtool.c                 |   64 ++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+), 2 deletions(-)

--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -18,7 +18,8 @@
 #include <objtool/builtin.h>
 #include <objtool/objtool.h>
 
-bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux, mcount, noinstr;
+bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
+     validate_dup, vmlinux, mcount, noinstr, backup;
 
 static const char * const check_usage[] = {
 	"objtool check [<options>] file.o",
@@ -37,6 +38,7 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('n', "noinstr", &noinstr, "noinstr validation for vmlinux.o"),
 	OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
 	OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),
+	OPT_BOOLEAN('B', "backup", &backup, "create .obj files before modification"),
 	OPT_END(),
 };
 
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -8,7 +8,8 @@
 #include <subcmd/parse-options.h>
 
 extern const struct option check_options[];
-extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux, mcount, noinstr;
+extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
+            validate_dup, vmlinux, mcount, noinstr, backup;
 
 extern int cmd_check(int argc, const char **argv);
 extern int cmd_orc(int argc, const char **argv);
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -17,6 +17,7 @@
 #include <stdbool.h>
 #include <string.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <subcmd/exec-cmd.h>
 #include <subcmd/pager.h>
 #include <linux/kernel.h>
@@ -44,6 +45,64 @@ bool help;
 const char *objname;
 static struct objtool_file file;
 
+static bool objtool_create_backup(const char *_objname)
+{
+	int len = strlen(_objname);
+	char *buf, *base, *name = malloc(len+3);
+	int s, d, l, t;
+
+	if (!name) {
+		perror("failed backup name malloc");
+		return false;
+	}
+
+	strcpy(name, _objname);
+	strcpy(name + len, "bj");
+
+	d = open(name, O_CREAT|O_WRONLY|O_TRUNC, 0644);
+	if (d < 0) {
+		perror("failed to create backup file");
+		return false;
+	}
+
+	s = open(_objname, O_RDONLY);
+	if (s < 0) {
+		perror("failed to open orig file");
+		return false;
+	}
+
+	buf = malloc(4096);
+	if (!buf) {
+		perror("failed backup data malloc");
+		return false;
+	}
+
+	while ((l = read(s, buf, 4096)) > 0) {
+		base = buf;
+		do {
+			t = write(d, base, l);
+			if (t < 0) {
+				perror("failed backup write");
+				return false;
+			}
+			base += t;
+			l -= t;
+		} while (l);
+	}
+
+	if (l < 0) {
+		perror("failed backup read");
+		return false;
+	}
+
+	free(name);
+	free(buf);
+	close(d);
+	close(s);
+
+	return true;
+}
+
 struct objtool_file *objtool_open_read(const char *_objname)
 {
 	if (objname) {
@@ -59,6 +118,11 @@ struct objtool_file *objtool_open_read(c
 	if (!file.elf)
 		return NULL;
 
+	if (backup && !objtool_create_backup(objname)) {
+		WARN("can't create backup file");
+		return NULL;
+	}
+
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
 	INIT_LIST_HEAD(&file.static_call_list);