Make sure FreeBSD binaries without .note.ABI-tag section work

correctly and do not match a colliding Debian GNU/kFreeBSD
brandinfo statements.
For this mark the Debian GNU/kFreeBSD brandinfo that it must have
an .note.ABI-tag section and ignore the old EI_OSABI brandinfo
when comparing a possibly colliding set of options.

Due to SYSINIT we add the brandinfo in a non-deterministic order,
so native FreeBSD is not always first. We may want to consider
to force native FreeBSD to come first as well.

The only way a problem could currently be noticed is when running an
i386 binary without the .note.ABI-tag on amd64 and the Debian GNU/kFreeBSD
brandinfo  was matched first,  as the fallback to ld-elf32.so.1 does
not exist in that case.

Reported and tested by:	ticso
In collaboration with:	kib
MFC after:		3 days

5 files changed, 19 insertions, 10 deletions

diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
index ea48b25..d5e7a6e 100644
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -118,7 +118,7 @@ static Elf64_Brandinfo kfreebsd_brand_info = {
 	.sysvec		= &elf64_freebsd_sysvec,
 	.interp_newpath	= NULL,
 	.brand_note	= &elf64_kfreebsd_brandnote,
-	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE
+	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE_MANDATORY
 };
 
 SYSINIT(kelf64, SI_SUB_EXEC, SI_ORDER_ANY,
diff --git a/sys/compat/ia32/ia32_sysvec.c b/sys/compat/ia32/ia32_sysvec.c
index 5c2c571..46e0b80 100644
--- a/sys/compat/ia32/ia32_sysvec.c
+++ b/sys/compat/ia32/ia32_sysvec.c
@@ -180,7 +180,7 @@ static Elf32_Brandinfo kia32_brand_info = {
 	.interp_path	= "/lib/ld.so.1",
 	.sysvec		= &ia32_freebsd_sysvec,
 	.brand_note	= &elf32_kfreebsd_brandnote,
-	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE
+	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE_MANDATORY
 };
 
 SYSINIT(kia32, SI_SUB_EXEC, SI_ORDER_ANY,
diff --git a/sys/i386/i386/elf_machdep.c b/sys/i386/i386/elf_machdep.c
index a4ff9e2..abfe147 100644
--- a/sys/i386/i386/elf_machdep.c
+++ b/sys/i386/i386/elf_machdep.c
@@ -117,7 +117,7 @@ static Elf32_Brandinfo kfreebsd_brand_info = {
 	.sysvec		= &elf32_freebsd_sysvec,
 	.interp_newpath	= NULL,
 	.brand_note	= &elf32_kfreebsd_brandnote,
-	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE
+	.flags		= BI_CAN_EXEC_DYN | BI_BRAND_NOTE_MANDATORY
 };
 
 SYSINIT(kelf32, SI_SUB_EXEC, SI_ORDER_ANY,
diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index 6803523..ba5833a 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -238,8 +238,10 @@ __elfN(get_brandinfo)(struct image_params *imgp, const char *interp,
 	/* Look for an ".note.ABI-tag" ELF section */
 	for (i = 0; i < MAX_BRANDS; i++) {
 		bi = elf_brand_list[i];
-		if (bi != NULL && hdr->e_machine == bi->machine &&
-		    (bi->flags & BI_BRAND_NOTE) != 0) {
+		if (bi == NULL)
+			continue;
+		if (hdr->e_machine == bi->machine && (bi->flags &
+		    (BI_BRAND_NOTE|BI_BRAND_NOTE_MANDATORY)) != 0) {
 			ret = __elfN(check_note)(imgp, bi->brand_note, osrel);
 			if (ret)
 				return (bi);
@@ -249,7 +251,9 @@ __elfN(get_brandinfo)(struct image_params *imgp, const char *interp,
 	/* If the executable has a brand, search for it in the brand list. */
 	for (i = 0; i < MAX_BRANDS; i++) {
 		bi = elf_brand_list[i];
-		if (bi != NULL && hdr->e_machine == bi->machine &&
+		if (bi == NULL || bi->flags & BI_BRAND_NOTE_MANDATORY)
+			continue;
+		if (hdr->e_machine == bi->machine &&
 		    (hdr->e_ident[EI_OSABI] == bi->brand ||
 		    strncmp((const char *)&hdr->e_ident[OLD_EI_BRAND],
 		    bi->compat_3_brand, strlen(bi->compat_3_brand)) == 0))
@@ -260,7 +264,9 @@ __elfN(get_brandinfo)(struct image_params *imgp, const char *interp,
 	if (interp != NULL) {
 		for (i = 0; i < MAX_BRANDS; i++) {
 			bi = elf_brand_list[i];
-			if (bi != NULL && hdr->e_machine == bi->machine &&
+			if (bi == NULL || bi->flags & BI_BRAND_NOTE_MANDATORY)
+				continue;
+			if (hdr->e_machine == bi->machine &&
 			    strcmp(interp, bi->interp_path) == 0)
 				return (bi);
 		}
@@ -269,7 +275,9 @@ __elfN(get_brandinfo)(struct image_params *imgp, const char *interp,
 	/* Lacking a recognized interpreter, try the default brand */
 	for (i = 0; i < MAX_BRANDS; i++) {
 		bi = elf_brand_list[i];
-		if (bi != NULL && hdr->e_machine == bi->machine &&
+		if (bi == NULL || bi->flags & BI_BRAND_NOTE_MANDATORY)
+			continue;
+		if (hdr->e_machine == bi->machine &&
 		    __elfN(fallback_brand) == bi->brand)
 			return (bi);
 	}
diff --git a/sys/sys/imgact_elf.h b/sys/sys/imgact_elf.h
index 3eecf85..4ccee5d 100644
--- a/sys/sys/imgact_elf.h
+++ b/sys/sys/imgact_elf.h
@@ -74,8 +74,9 @@ typedef struct {
 	const char *interp_newpath;
 	int flags;
 	Elf_Brandnote *brand_note;
-#define	BI_CAN_EXEC_DYN	0x0001
-#define	BI_BRAND_NOTE	0x0002
+#define	BI_CAN_EXEC_DYN		0x0001
+#define	BI_BRAND_NOTE		0x0002	/* May have note.ABI-tag section. */
+#define	BI_BRAND_NOTE_MANDATORY	0x0004	/* Must have note.ABI-tag section. */
 } __ElfN(Brandinfo);
 
 __ElfType(Auxargs);