omitrbp

commit 5c021778106dc47481a2e2c57bb6d9a15325126e
Author: Christos Margiolis <christos@margiolis.net>
Date:   Sat, 18 Mar 2023 20:19:04 +0200

initial commit

Diffstat:
A
LICENSE
 | 
20
++++++++++++++++++++
A
Makefile
 | 
8
++++++++
A
README
 | 
4
++++
A
omitrbp.1
 | 
23
+++++++++++++++++++++++
A
omitrbp.c
 | 
184
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

5 files changed, 239 insertions(+), 0 deletions(-)
diff --git a/LICENSE b/LICENSE
@@ -0,0 +1,20 @@
+MIT License
+
+(c) 2023-Present Christos Margiolis <christos@FreeBSD.org>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the “Software”), to deal in
+the Software without restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+Software, and to permit persons to whom the Software is furnished to do so, 
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/Makefile b/Makefile
@@ -0,0 +1,8 @@
+# $FreeBSD$
+
+PROG=		omitrbp
+SRCS=		${PROG}.c
+MAN=		${PROG}.1
+LDFLAGS+=	-lelf
+
+.include <bsd.prog.mk>
diff --git a/README b/README
@@ -0,0 +1,4 @@
+omitrbp
+=======
+
+omitrbp prints all kernel functions that omit their frame pointer (rbp).
diff --git a/omitrbp.1 b/omitrbp.1
@@ -0,0 +1,23 @@
+.Dd March 18, 2023
+.Dt OMITRBP 1
+.Os
+.Sh NAME
+.Nm omitrbp
+.Nd find kernel functions that omit the frame pointer
+.Sh SYNOPSIS
+.Nm
+.Op Fl f
+.Sh DESCRIPTION
+.Nm
+uses the kernel bootfile's ELF info to find all functions that omit the frame
+pointer (rbp). If the
+.Fl f
+option is specified,
+.Nm
+will print only the functions that do not push the frame pointer in the the
+first instruction.
+.Sh SEE ALSO
+.Xr elf 3 ,
+.Xr gelf 3
+.Sh AUTHORS
+.An Christos Margiolis Aq Mt christos@FreeBSD.org
diff --git a/omitrbp.c b/omitrbp.c
@@ -0,0 +1,184 @@
+#include <sys/param.h>
+#include <sys/sysctl.h>
+
+#include <err.h>
+#include <fcntl.h>
+#include <gelf.h>
+#include <libelf.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+struct section {
+	GElf_Shdr	sh;
+	Elf_Scn		*scn;
+	const char	*name;
+};
+
+static struct section *sl;
+static size_t shnum;
+static int first_instr = 0;
+
+static void
+print_rbp_ommited(const char *func, uint64_t lo, uint64_t hi)
+{
+	Elf_Data *d;
+	struct section *s;
+	uint8_t *buf;
+	uint64_t addr;
+	int i;
+
+	for (i = 1; i < shnum; i++) {
+		s = &sl[i];
+		if (strcmp(s->name, ".text") != 0 ||
+		    s->sh.sh_type != SHT_PROGBITS)
+			continue;
+		(void)elf_errno();
+		if ((d = elf_getdata(s->scn, NULL)) == NULL) {
+			if (elf_errno() != 0)
+				warnx("elf_getdata(): %s", elf_errmsg(-1));
+			continue;
+		}
+		if (d->d_size <= 0 || d->d_buf == NULL)
+			continue;
+		buf = d->d_buf;
+		addr = s->sh.sh_addr + d->d_off;
+		while (addr != lo) {
+			addr++;
+			buf++;
+		}
+		if (first_instr) {
+			if (*buf != 0x55)
+				puts(func);
+		} else {
+			int found = 0;
+
+			while (addr != hi) {
+				if (*buf == 0x55)
+					found = 1;
+				addr++;
+				buf++;
+			}
+			if (!found)
+				puts(func);
+		}
+		return;
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	Elf *elf;
+	Elf_Scn *scn;
+	Elf_Data *d;
+	GElf_Shdr sh;
+	GElf_Sym sym;
+	struct section *s;
+	uint64_t lo, hi;
+	uint32_t stab;
+	const char *name, *func;
+	char bootfile[BUFSIZ];
+	size_t shstrndx, ndx, slen;
+	int fd, len, i, j, ch;
+
+	while ((ch = getopt(argc, argv, "f")) != -1) {
+		switch (ch) {
+		case 'f':
+			first_instr = 1;
+			break;
+		case '?':
+		default:
+			fprintf(stderr, "usage: %s [-f]\n", argv[0]);
+			exit(1);
+		}
+	}
+	argc -= optind;
+	argv += optind;
+
+	slen = sizeof(bootfile);
+	if (sysctlbyname("kern.bootfile", bootfile, &slen, NULL, 0) != 0)
+		strlcpy(bootfile, "/boot/kernel/kernel", sizeof(bootfile));
+
+	if (elf_version(EV_CURRENT) == EV_NONE)
+		errx(1, "elf_version(): %s", elf_errmsg(-1));
+	if ((fd = open(bootfile, O_RDONLY)) < 0)
+		err(1, "open(%s)", bootfile);
+	if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL)
+		errx(1, "elf_begin(): %s", elf_errmsg(-1));
+	if (elf_kind(elf) == ELF_K_NONE)
+		errx(1, "not an ELF file: %s", bootfile);
+
+	if (!elf_getshnum(elf, &shnum))
+		errx(1, "elf_getshnum(): %s", elf_errmsg(-1));
+	if ((sl = malloc(shnum * sizeof(struct section))) == NULL)
+		err(1, "malloc");
+	if (!elf_getshstrndx(elf, &shstrndx))
+		errx(1, "elf_getshstrndx(): %s", elf_errmsg(-1));
+	if ((scn = elf_getscn(elf, 0)) == NULL)
+		errx(1, "elf_getscn(): %s", elf_errmsg(-1));
+	(void)elf_errno();
+
+	do {
+		if (gelf_getshdr(scn, &sh) == NULL) {
+			warnx("gelf_getshdr(): %s", elf_errmsg(-1));
+			(void)elf_errno();
+			continue;
+		}
+		if ((name = elf_strptr(elf, shstrndx, sh.sh_name)) == NULL)
+			(void)elf_errno();
+		if ((ndx = elf_ndxscn(scn)) == SHN_UNDEF && elf_errno() != 0) {
+			warnx("elf_ndxscn(): %s", elf_errmsg(-1));
+			continue;
+		}
+		if (ndx >= shnum)
+			continue;
+		s = &sl[ndx];
+		s->scn = scn;
+		s->sh = sh;
+		s->name = name;
+	} while ((scn = elf_nextscn(elf, scn)) != NULL);
+	if (elf_errno() != 0)
+		warnx("elf_nextscn(): %s", elf_errmsg(-1));
+
+	for (i = 1; i < shnum; i++) {
+		s = &sl[i];
+		if (s->sh.sh_type != SHT_SYMTAB && s->sh.sh_type != SHT_DYNSYM)
+			continue;
+		if (s->sh.sh_link >= shnum)
+			continue;
+		stab = s->sh.sh_link;
+		(void)elf_errno();
+		if ((d = elf_getdata(s->scn, NULL)) == NULL) {
+			if (elf_errno() != 0)
+				warnx("elf_getdata(): %s", elf_errmsg(-1));
+			continue;
+		}
+		if (d->d_size <= 0)
+			continue;
+		if (s->sh.sh_entsize == 0)
+			continue;
+		len = (int)(s->sh.sh_size / s->sh.sh_entsize);
+		if (len > INT_MAX)
+			continue;
+		for (j = 0; j < len; j++) {
+			if (gelf_getsym(d, j, &sym) != &sym) {
+				warnx("gelf_getsym(): %s", elf_errmsg(-1));
+				continue;
+			}
+			if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
+				continue;
+			lo = sym.st_value;
+			hi = sym.st_value + sym.st_size;
+			if ((func = elf_strptr(elf, stab, sym.st_name)) != NULL)
+				print_rbp_ommited(func, lo, hi);
+		}
+	}
+
+	free(sl);
+	close(fd);
+	elf_end(elf);
+
+	return (0);
+}