binfmt_flat: Remove shared library support

In a recent discussion[1] it was reported that the binfmt_flat library
support was only ever used on m68k and even on m68k has not been used
in a very long time.

The structure of binfmt_flat is different from all of the other binfmt
implementations because of this shared library support and it made
life and code review more effort when I refactored the code in fs/exec.c.

Since in practice the code is dead remove the binfmt_flat shared library
support and make maintenance of the code easier.

[1] https://lkml.kernel.org/r/81788b56-5b15-7308-38c7-c7f2502c4e15@linux-m68k.org

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Acked-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARM
Tested-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/87levzzts4.fsf_-_@email.froward.int.ebiederm.org

arch/arm/configs/lpc18xx_defconfig

@@ -30,7 +30,6 @@ CONFIG_ARM_APPENDED_DTB=y
 # CONFIG_BLK_DEV_BSG is not set
 CONFIG_BINFMT_FLAT=y
 CONFIG_BINFMT_ZFLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 # CONFIG_COREDUMP is not set
 CONFIG_NET=y
 CONFIG_PACKET=y

arch/arm/configs/mps2_defconfig

@@ -23,7 +23,6 @@ CONFIG_PREEMPT_VOLUNTARY=y
 CONFIG_ZBOOT_ROM_TEXT=0x0
 CONFIG_ZBOOT_ROM_BSS=0x0
 CONFIG_BINFMT_FLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 # CONFIG_COREDUMP is not set
 # CONFIG_SUSPEND is not set
 CONFIG_NET=y

arch/arm/configs/stm32_defconfig

@@ -28,7 +28,6 @@ CONFIG_ZBOOT_ROM_BSS=0x0
 CONFIG_XIP_KERNEL=y
 CONFIG_XIP_PHYS_ADDR=0x08008000
 CONFIG_BINFMT_FLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 # CONFIG_COREDUMP is not set
 CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y

arch/arm/configs/vf610m4_defconfig

@@ -18,7 +18,6 @@ CONFIG_XIP_KERNEL=y
 CONFIG_XIP_PHYS_ADDR=0x0f000080
 CONFIG_BINFMT_FLAT=y
 CONFIG_BINFMT_ZFLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 # CONFIG_SUSPEND is not set
 # CONFIG_UEVENT_HELPER is not set
 # CONFIG_STANDALONE is not set

arch/sh/configs/rsk7201_defconfig

@@ -25,7 +25,6 @@ CONFIG_CMDLINE_OVERWRITE=y
 CONFIG_CMDLINE="console=ttySC0,115200 earlyprintk=serial ignore_loglevel"
 CONFIG_BINFMT_FLAT=y
 CONFIG_BINFMT_ZFLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 CONFIG_PM=y
 CONFIG_CPU_IDLE=y
 # CONFIG_STANDALONE is not set

arch/sh/configs/rsk7203_defconfig

@@ -30,7 +30,6 @@ CONFIG_CMDLINE_OVERWRITE=y
 CONFIG_CMDLINE="console=ttySC0,115200 earlyprintk=serial ignore_loglevel"
 CONFIG_BINFMT_FLAT=y
 CONFIG_BINFMT_ZFLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 CONFIG_PM=y
 CONFIG_CPU_IDLE=y
 CONFIG_NET=y

arch/sh/configs/se7206_defconfig

@@ -40,7 +40,6 @@ CONFIG_CMDLINE_OVERWRITE=y
 CONFIG_CMDLINE="console=ttySC3,115200 ignore_loglevel earlyprintk=serial"
 CONFIG_BINFMT_FLAT=y
 CONFIG_BINFMT_ZFLAT=y
-CONFIG_BINFMT_SHARED_FLAT=y
 CONFIG_BINFMT_MISC=y
 CONFIG_NET=y
 CONFIG_PACKET=y

fs/Kconfig.binfmt

@@ -142,12 +142,6 @@ config BINFMT_ZFLAT
 	help
 	  Support FLAT format compressed binaries
 
-config BINFMT_SHARED_FLAT
-	bool "Enable shared FLAT support"
-	depends on BINFMT_FLAT
-	help
-	  Support FLAT shared libraries
-
 config HAVE_AOUT
        def_bool n
 

fs/binfmt_flat.c

@@ -68,11 +68,7 @@
 #define RELOC_FAILED 0xff00ff01		/* Relocation incorrect somewhere */
 #define UNLOADED_LIB 0x7ff000ff		/* Placeholder for unused library */
 
-#ifdef CONFIG_BINFMT_SHARED_FLAT
+#define MAX_SHARED_LIBS			(1)
-#define	MAX_SHARED_LIBS			(4)
-#else
-#define	MAX_SHARED_LIBS			(1)
-#endif
 
 #ifdef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
 #define DATA_START_OFFSET_WORDS		(0)
@@ -92,10 +88,6 @@ struct lib_info {
 	} lib_list[MAX_SHARED_LIBS];
 };
 
-#ifdef CONFIG_BINFMT_SHARED_FLAT
-static int load_flat_shared_library(int id, struct lib_info *p);
-#endif
-
 static int load_flat_binary(struct linux_binprm *);
 
 static struct linux_binfmt flat_format = {
@@ -307,51 +299,18 @@ out_free:
 /****************************************************************************/
 
 static unsigned long
-calc_reloc(unsigned long r, struct lib_info *p, int curid, int internalp)
+calc_reloc(unsigned long r, struct lib_info *p)
 {
 	unsigned long addr;
-	int id;
 	unsigned long start_brk;
 	unsigned long start_data;
 	unsigned long text_len;
 	unsigned long start_code;
 
-#ifdef CONFIG_BINFMT_SHARED_FLAT
+	start_brk = p->lib_list[0].start_brk;
-	if (r == 0)
+	start_data = p->lib_list[0].start_data;
-		id = curid;	/* Relocs of 0 are always self referring */
+	start_code = p->lib_list[0].start_code;
-	else {
+	text_len = p->lib_list[0].text_len;
-		id = (r >> 24) & 0xff;	/* Find ID for this reloc */
-		r &= 0x00ffffff;	/* Trim ID off here */
-	}
-	if (id >= MAX_SHARED_LIBS) {
-		pr_err("reference 0x%lx to shared library %d", r, id);
-		goto failed;
-	}
-	if (curid != id) {
-		if (internalp) {
-			pr_err("reloc address 0x%lx not in same module "
-			       "(%d != %d)", r, curid, id);
-			goto failed;
-		} else if (!p->lib_list[id].loaded &&
-			   load_flat_shared_library(id, p) < 0) {
-			pr_err("failed to load library %d", id);
-			goto failed;
-		}
-		/* Check versioning information (i.e. time stamps) */
-		if (p->lib_list[id].build_date && p->lib_list[curid].build_date &&
-				p->lib_list[curid].build_date < p->lib_list[id].build_date) {
-			pr_err("library %d is younger than %d", id, curid);
-			goto failed;
-		}
-	}
-#else
-	id = 0;
-#endif
-
-	start_brk = p->lib_list[id].start_brk;
-	start_data = p->lib_list[id].start_data;
-	start_code = p->lib_list[id].start_code;
-	text_len = p->lib_list[id].text_len;
 
 	if (r > start_brk - start_data + text_len) {
 		pr_err("reloc outside program 0x%lx (0 - 0x%lx/0x%lx)",
@@ -443,7 +402,7 @@ static inline u32 __user *skip_got_header(u32 __user *rp)
 }
 
 static int load_flat_file(struct linux_binprm *bprm,
-		struct lib_info *libinfo, int id, unsigned long *extra_stack)
+		struct lib_info *libinfo, unsigned long *extra_stack)
 {
 	struct flat_hdr *hdr;
 	unsigned long textpos, datapos, realdatastart;
@@ -495,14 +454,6 @@ static int load_flat_file(struct linux_binprm *bprm,
 		goto err;
 	}
 
-	/* Don't allow old format executables to use shared libraries */
-	if (rev == OLD_FLAT_VERSION && id != 0) {
-		pr_err("shared libraries are not available before rev 0x%lx\n",
-		       FLAT_VERSION);
-		ret = -ENOEXEC;
-		goto err;
-	}
-
 	/*
 	 * fix up the flags for the older format,  there were all kinds
 	 * of endian hacks,  this only works for the simple cases
@@ -553,15 +504,13 @@ static int load_flat_file(struct linux_binprm *bprm,
 	}
 
 	/* Flush all traces of the currently running executable */
-	if (id == 0) {
+	ret = begin_new_exec(bprm);
-		ret = begin_new_exec(bprm);
+	if (ret)
-		if (ret)
+		goto err;
-			goto err;
 
-		/* OK, This is the point of no return */
+	/* OK, This is the point of no return */
-		set_personality(PER_LINUX_32BIT);
+	set_personality(PER_LINUX_32BIT);
-		setup_new_exec(bprm);
+	setup_new_exec(bprm);
-	}
 
 	/*
 	 * calculate the extra space we need to map in
@@ -741,42 +690,40 @@ static int load_flat_file(struct linux_binprm *bprm,
 	text_len -= sizeof(struct flat_hdr); /* the real code len */
 
 	/* The main program needs a little extra setup in the task structure */
-	if (id == 0) {
+	current->mm->start_code = start_code;
-		current->mm->start_code = start_code;
+	current->mm->end_code = end_code;
-		current->mm->end_code = end_code;
+	current->mm->start_data = datapos;
-		current->mm->start_data = datapos;
+	current->mm->end_data = datapos + data_len;
-		current->mm->end_data = datapos + data_len;
+	/*
-		/*
+	 * set up the brk stuff, uses any slack left in data/bss/stack
-		 * set up the brk stuff, uses any slack left in data/bss/stack
+	 * allocation.  We put the brk after the bss (between the bss
-		 * allocation.  We put the brk after the bss (between the bss
+	 * and stack) like other platforms.
-		 * and stack) like other platforms.
+	 * Userspace code relies on the stack pointer starting out at
-		 * Userspace code relies on the stack pointer starting out at
+	 * an address right at the end of a page.
-		 * an address right at the end of a page.
+	 */
-		 */
+	current->mm->start_brk = datapos + data_len + bss_len;
-		current->mm->start_brk = datapos + data_len + bss_len;
+	current->mm->brk = (current->mm->start_brk + 3) & ~3;
-		current->mm->brk = (current->mm->start_brk + 3) & ~3;
 #ifndef CONFIG_MMU
-		current->mm->context.end_brk = memp + memp_size - stack_len;
+	current->mm->context.end_brk = memp + memp_size - stack_len;
 #endif
-	}
 
 	if (flags & FLAT_FLAG_KTRACE) {
 		pr_info("Mapping is %lx, Entry point is %x, data_start is %x\n",
 			textpos, 0x00ffffff&ntohl(hdr->entry), ntohl(hdr->data_start));
 		pr_info("%s %s: TEXT=%lx-%lx DATA=%lx-%lx BSS=%lx-%lx\n",
-			id ? "Lib" : "Load", bprm->filename,
+			"Load", bprm->filename,
 			start_code, end_code, datapos, datapos + data_len,
 			datapos + data_len, (datapos + data_len + bss_len + 3) & ~3);
 	}
 
 	/* Store the current module values into the global library structure */
-	libinfo->lib_list[id].start_code = start_code;
+	libinfo->lib_list[0].start_code = start_code;
-	libinfo->lib_list[id].start_data = datapos;
+	libinfo->lib_list[0].start_data = datapos;
-	libinfo->lib_list[id].start_brk = datapos + data_len + bss_len;
+	libinfo->lib_list[0].start_brk = datapos + data_len + bss_len;
-	libinfo->lib_list[id].text_len = text_len;
+	libinfo->lib_list[0].text_len = text_len;
-	libinfo->lib_list[id].loaded = 1;
+	libinfo->lib_list[0].loaded = 1;
-	libinfo->lib_list[id].entry = (0x00ffffff & ntohl(hdr->entry)) + textpos;
+	libinfo->lib_list[0].entry = (0x00ffffff & ntohl(hdr->entry)) + textpos;
-	libinfo->lib_list[id].build_date = ntohl(hdr->build_date);
+	libinfo->lib_list[0].build_date = ntohl(hdr->build_date);
 
 	/*
 	 * We just load the allocations into some temporary memory to
@@ -799,7 +746,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 			if (rp_val == 0xffffffff)
 				break;
 			if (rp_val) {
-				addr = calc_reloc(rp_val, libinfo, id, 0);
+				addr = calc_reloc(rp_val, libinfo);
 				if (addr == RELOC_FAILED) {
 					ret = -ENOEXEC;
 					goto err;
@@ -835,7 +782,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 				return -EFAULT;
 			relval = ntohl(tmp);
 			addr = flat_get_relocate_addr(relval);
-			rp = (u32 __user *)calc_reloc(addr, libinfo, id, 1);
+			rp = (u32 __user *)calc_reloc(addr, libinfo);
 			if (rp == (u32 __user *)RELOC_FAILED) {
 				ret = -ENOEXEC;
 				goto err;
@@ -858,7 +805,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 					 */
 					addr = ntohl((__force __be32)addr);
 				}
-				addr = calc_reloc(addr, libinfo, id, 0);
+				addr = calc_reloc(addr, libinfo);
 				if (addr == RELOC_FAILED) {
 					ret = -ENOEXEC;
 					goto err;
@@ -886,7 +833,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 	/* zero the BSS,  BRK and stack areas */
 	if (clear_user((void __user *)(datapos + data_len), bss_len +
 		       (memp + memp_size - stack_len -		/* end brk */
-		       libinfo->lib_list[id].start_brk) +	/* start brk */
+		       libinfo->lib_list[0].start_brk) +	/* start brk */
 		       stack_len))
 		return -EFAULT;
 
@@ -896,49 +843,6 @@ err:
 }
 
 
-/****************************************************************************/
-#ifdef CONFIG_BINFMT_SHARED_FLAT
-
-/*
- * Load a shared library into memory.  The library gets its own data
- * segment (including bss) but not argv/argc/environ.
- */
-
-static int load_flat_shared_library(int id, struct lib_info *libs)
-{
-	/*
-	 * This is a fake bprm struct; only the members "buf", "file" and
-	 * "filename" are actually used.
-	 */
-	struct linux_binprm bprm;
-	int res;
-	char buf[16];
-	loff_t pos = 0;
-
-	memset(&bprm, 0, sizeof(bprm));
-
-	/* Create the file name */
-	sprintf(buf, "/lib/lib%d.so", id);
-
-	/* Open the file up */
-	bprm.filename = buf;
-	bprm.file = open_exec(bprm.filename);
-	res = PTR_ERR(bprm.file);
-	if (IS_ERR(bprm.file))
-		return res;
-
-	res = kernel_read(bprm.file, bprm.buf, BINPRM_BUF_SIZE, &pos);
-
-	if (res >= 0)
-		res = load_flat_file(&bprm, libs, id, NULL);
-
-	allow_write_access(bprm.file);
-	fput(bprm.file);
-
-	return res;
-}
-
-#endif /* CONFIG_BINFMT_SHARED_FLAT */
 /****************************************************************************/
 
 /*
@@ -971,7 +875,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
 	stack_len += (bprm->envc + 1) * sizeof(char *);   /* the envp array */
 	stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN);
 
-	res = load_flat_file(bprm, &libinfo, 0, &stack_len);
+	res = load_flat_file(bprm, &libinfo, &stack_len);
 	if (res < 0)
 		return res;
 
@@ -1016,20 +920,6 @@ static int load_flat_binary(struct linux_binprm *bprm)
 	 */
 	start_addr = libinfo.lib_list[0].entry;
 
-#ifdef CONFIG_BINFMT_SHARED_FLAT
-	for (i = MAX_SHARED_LIBS-1; i > 0; i--) {
-		if (libinfo.lib_list[i].loaded) {
-			/* Push previos first to call address */
-			unsigned long __user *sp;
-			current->mm->start_stack -= sizeof(unsigned long);
-			sp = (unsigned long __user *)current->mm->start_stack;
-			if (put_user(start_addr, sp))
-				return -EFAULT;
-			start_addr = libinfo.lib_list[i].entry;
-		}
-	}
-#endif
-
 #ifdef FLAT_PLAT_INIT
 	FLAT_PLAT_INIT(regs);
 #endif