From 4a27bf128b108d90412190c06a54ebac36a8ca2e Mon Sep 17 00:00:00 2001
From: Marcin Wojtas <mw@FreeBSD.org>
Date: Fri, 21 May 2021 11:19:31 +0200
Subject: [PATCH] usr.bin/elfctl: Allow for cross-endian operations.

Detect if host endian is different than target endian and swap
byte order of ELF note fields instead of failing.

Submitted by: Dawid Gorecki <dgr@semihalf.com>
Reviewed by: imp
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D29550
---
 usr.bin/elfctl/elfctl.c | 55 +++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 19 deletions(-)

diff --git a/usr.bin/elfctl/elfctl.c b/usr.bin/elfctl/elfctl.c
index bcdd1be394a9..41660fc4acd5 100644
--- a/usr.bin/elfctl/elfctl.c
+++ b/usr.bin/elfctl/elfctl.c
@@ -52,10 +52,10 @@
 __FBSDID("$FreeBSD$");
 
 static bool convert_to_feature_val(char *, uint32_t *);
-static bool edit_file_features(Elf *, int, int, char *);
-static bool get_file_features(Elf *, int, int, uint32_t *, uint64_t *);
+static bool edit_file_features(Elf *, int, int, char *, bool);
+static bool get_file_features(Elf *, int, int, uint32_t *, uint64_t *, bool);
 static void print_features(void);
-static bool print_file_features(Elf *, int, int, char *);
+static bool print_file_features(Elf *, int, int, char *, bool);
 static void usage(void);
 
 struct ControlFeatures {
@@ -81,9 +81,11 @@ static struct option long_opts[] = {
 };
 
 #if BYTE_ORDER == LITTLE_ENDIAN
-#define SUPPORTED_ENDIAN ELFDATA2LSB
+#define	HOST_ENDIAN	ELFDATA2LSB
+#define	SWAP_ENDIAN	ELFDATA2MSB
 #else
-#define SUPPORTED_ENDIAN ELFDATA2MSB
+#define	HOST_ENDIAN 	ELFDATA2MSB
+#define	SWAP_ENDIAN	ELFDATA2LSB
 #endif
 
 static bool iflag;
@@ -96,7 +98,7 @@ main(int argc, char **argv)
 	Elf_Kind kind;
 	int ch, fd, retval;
 	char *features;
-	bool editfeatures, lflag;
+	bool editfeatures, lflag, endian_swap;
 
 	lflag = 0;
 	editfeatures = false;
@@ -165,24 +167,25 @@ main(int argc, char **argv)
 			retval = 1;
 			goto fail;
 		}
-		/*
-		 * XXX need to support cross-endian operation, but for now
-		 * exit on error rather than misbehaving.
-		 */
-		if (ehdr.e_ident[EI_DATA] != SUPPORTED_ENDIAN) {
-			warnx("file endianness must match host");
+
+		if (ehdr.e_ident[EI_DATA] == HOST_ENDIAN) {
+			endian_swap = false;
+		} else if (ehdr.e_ident[EI_DATA] == SWAP_ENDIAN) {
+			endian_swap = true;
+		} else {
+			warnx("file endianness unknown");
 			retval = 1;
 			goto fail;
 		}
 
 		if (!editfeatures) {
 			if (!print_file_features(elf, ehdr.e_phnum, fd,
-			    argv[0])) {
+			    argv[0], endian_swap)) {
 				retval = 1;
 				goto fail;
 			}
 		} else if (!edit_file_features(elf, ehdr.e_phnum, fd,
-		    features)) {
+		    features, endian_swap)) {
 			retval = 1;
 			goto fail;
 		}
@@ -286,12 +289,13 @@ convert_to_feature_val(char *feature_str, uint32_t *feature_val)
 }
 
 static bool
-edit_file_features(Elf *elf, int phcount, int fd, char *val)
+edit_file_features(Elf *elf, int phcount, int fd, char *val, bool endian_swap)
 {
 	uint32_t features;
 	uint64_t off;
 
-	if (!get_file_features(elf, phcount, fd, &features, &off)) {
+	if (!get_file_features(elf, phcount, fd, &features, &off,
+	    endian_swap)) {
 		warnx("NT_FREEBSD_FEATURE_CTL note not found");
 		return (false);
 	}
@@ -299,6 +303,9 @@ edit_file_features(Elf *elf, int phcount, int fd, char *val)
 	if (!convert_to_feature_val(val, &features))
 		return (false);
 
+	if (endian_swap)
+		features = bswap32(features);
+
 	if (lseek(fd, off, SEEK_SET) == -1 ||
 	    write(fd, &features, sizeof(features)) <
 	    (ssize_t)sizeof(features)) {
@@ -320,12 +327,14 @@ print_features(void)
 }
 
 static bool
-print_file_features(Elf *elf, int phcount, int fd, char *filename)
+print_file_features(Elf *elf, int phcount, int fd, char *filename,
+    bool endian_swap)
 {
 	uint32_t features;
 	unsigned long i;
 
-	if (!get_file_features(elf, phcount, fd, &features, NULL)) {
+	if (!get_file_features(elf, phcount, fd, &features, NULL,
+	    endian_swap)) {
 		return (false);
 	}
 
@@ -344,7 +353,7 @@ print_file_features(Elf *elf, int phcount, int fd, char *filename)
 
 static bool
 get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
-    uint64_t *off)
+    uint64_t *off, bool endian_swap)
 {
 	GElf_Phdr phdr;
 	Elf_Note note;
@@ -379,6 +388,12 @@ get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 			}
 			read_total += sizeof(note);
 
+			if (endian_swap) {
+				note.n_namesz = bswap32(note.n_namesz);
+				note.n_descsz = bswap32(note.n_descsz);
+				note.n_type = bswap32(note.n_type);
+			}
+
 			/*
 			 * XXX: Name and descriptor are 4 byte aligned, however,
 			 * 	the size given doesn't include the padding.
@@ -430,6 +445,8 @@ get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 				free(name);
 				return (false);
 			}
+			if (endian_swap)
+				*features = bswap32(*features);
 			if (off != NULL)
 				*off = phdr.p_offset + read_total;
 			free(name);