Re: [PATCH] x86: Deprecate a.out support

[Linus Torvalds]

On Tue, Mar 5, 2019 at 6:59 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> We can at least deprecate it on x86...

I'd prefer to try to deprecate a.out core dumping first.. That's the
part that is actually broken, no?

In fact, I'd be happy to deprecate a.out entirely, but if somebody
_does_ complain, I'd like to be able to bring it back without the core
dumping.

Because I think the likeliihood that anybody cares about a.out core
dumps is basically zero. While the likelihood that we have some odd
old binary that is still a.out is slightly above zero.

So I'd be much happier with this if it was a two-stage thing where we
just delete a.out core dumping entirely first, and then deprecate even
running a.out binaries separately.

Because I think all the known *bugs* we had were with the core dumping
code, weren't they?

Removing it looks trivial. Untested patch attached.

Then I'd be much happier with your "let's deprecate a.out entirely" as
a second patch, because I think it's a unrelated issue and much more
likely to have somebody pipe up and say "hey, I have this sequence
that generates executables dynamically, and I use a.out because it's
much simpler than ELF, and now it's broken". Or something.

           Linus
 arch/x86/ia32/ia32_aout.c | 159 ----------------------------------------------
 fs/binfmt_aout.c          |  82 ------------------------
 2 files changed, 241 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index 7dbbe9ffda17..3c135084e1eb 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -39,82 +39,10 @@
 static int load_aout_binary(struct linux_binprm *);
 static int load_aout_library(struct file *);
 
-#ifdef CONFIG_COREDUMP
-static int aout_core_dump(struct coredump_params *);
-
-static unsigned long get_dr(int n)
-{
-	struct perf_event *bp = current->thread.ptrace_bps[n];
-	return bp ? bp->hw.info.address : 0;
-}
-
-/*
- * fill in the user structure for a core dump..
- */
-static void fill_dump(struct pt_regs *regs, struct user32 *dump)
-{
-	u32 fs, gs;
-	memset(dump, 0, sizeof(*dump));
-
-/* changed the size calculations - should hopefully work better. lbt */
-	dump->magic = CMAGIC;
-	dump->start_code = 0;
-	dump->start_stack = regs->sp & ~(PAGE_SIZE - 1);
-	dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
-	dump->u_dsize = ((unsigned long)
-			 (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
-	dump->u_dsize -= dump->u_tsize;
-	dump->u_debugreg[0] = get_dr(0);
-	dump->u_debugreg[1] = get_dr(1);
-	dump->u_debugreg[2] = get_dr(2);
-	dump->u_debugreg[3] = get_dr(3);
-	dump->u_debugreg[6] = current->thread.debugreg6;
-	dump->u_debugreg[7] = current->thread.ptrace_dr7;
-
-	if (dump->start_stack < 0xc0000000) {
-		unsigned long tmp;
-
-		tmp = (unsigned long) (0xc0000000 - dump->start_stack);
-		dump->u_ssize = tmp >> PAGE_SHIFT;
-	}
-
-	dump->regs.ebx = regs->bx;
-	dump->regs.ecx = regs->cx;
-	dump->regs.edx = regs->dx;
-	dump->regs.esi = regs->si;
-	dump->regs.edi = regs->di;
-	dump->regs.ebp = regs->bp;
-	dump->regs.eax = regs->ax;
-	dump->regs.ds = current->thread.ds;
-	dump->regs.es = current->thread.es;
-	savesegment(fs, fs);
-	dump->regs.fs = fs;
-	savesegment(gs, gs);
-	dump->regs.gs = gs;
-	dump->regs.orig_eax = regs->orig_ax;
-	dump->regs.eip = regs->ip;
-	dump->regs.cs = regs->cs;
-	dump->regs.eflags = regs->flags;
-	dump->regs.esp = regs->sp;
-	dump->regs.ss = regs->ss;
-
-#if 1 /* FIXME */
-	dump->u_fpvalid = 0;
-#else
-	dump->u_fpvalid = dump_fpu(regs, &dump->i387);
-#endif
-}
-
-#endif
-
 static struct linux_binfmt aout_format = {
 	.module		= THIS_MODULE,
 	.load_binary	= load_aout_binary,
 	.load_shlib	= load_aout_library,
-#ifdef CONFIG_COREDUMP
-	.core_dump	= aout_core_dump,
-#endif
-	.min_coredump	= PAGE_SIZE
 };
 
 static int set_brk(unsigned long start, unsigned long end)
@@ -126,93 +54,6 @@ static int set_brk(unsigned long start, unsigned long end)
 	return vm_brk(start, end - start);
 }
 
-#ifdef CONFIG_COREDUMP
-/*
- * These are the only things you should do on a core-file: use only these
- * macros to write out all the necessary info.
- */
-
-#include <linux/coredump.h>
-
-#define START_DATA(u)	(u.u_tsize << PAGE_SHIFT)
-#define START_STACK(u)	(u.start_stack)
-
-/*
- * Routine writes a core dump image in the current directory.
- * Currently only a stub-function.
- *
- * Note that setuid/setgid files won't make a core-dump if the uid/gid
- * changed due to the set[u|g]id. It's enforced by the "current->mm->dumpable"
- * field, which also makes sure the core-dumps won't be recursive if the
- * dumping of the process results in another error..
- */
-
-static int aout_core_dump(struct coredump_params *cprm)
-{
-	mm_segment_t fs;
-	int has_dumped = 0;
-	unsigned long dump_start, dump_size;
-	struct user32 dump;
-
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-	has_dumped = 1;
-
-	fill_dump(cprm->regs, &dump);
-
-	strncpy(dump.u_comm, current->comm, sizeof(current->comm));
-	dump.u_ar0 = offsetof(struct user32, regs);
-	dump.signal = cprm->siginfo->si_signo;
-
-	/*
-	 * If the size of the dump file exceeds the rlimit, then see
-	 * what would happen if we wrote the stack, but not the data
-	 * area.
-	 */
-	if ((dump.u_dsize + dump.u_ssize + 1) * PAGE_SIZE > cprm->limit)
-		dump.u_dsize = 0;
-
-	/* Make sure we have enough room to write the stack and data areas. */
-	if ((dump.u_ssize + 1) * PAGE_SIZE > cprm->limit)
-		dump.u_ssize = 0;
-
-	/* make sure we actually have a data and stack area to dump */
-	set_fs(USER_DS);
-	if (!access_ok((void *) (unsigned long)START_DATA(dump),
-		       dump.u_dsize << PAGE_SHIFT))
-		dump.u_dsize = 0;
-	if (!access_ok((void *) (unsigned long)START_STACK(dump),
-		       dump.u_ssize << PAGE_SHIFT))
-		dump.u_ssize = 0;
-
-	set_fs(KERNEL_DS);
-	/* struct user */
-	if (!dump_emit(cprm, &dump, sizeof(dump)))
-		goto end_coredump;
-	/* Now dump all of the user data.  Include malloced stuff as well */
-	if (!dump_skip(cprm, PAGE_SIZE - sizeof(dump)))
-		goto end_coredump;
-	/* now we start writing out the user space info */
-	set_fs(USER_DS);
-	/* Dump the data area */
-	if (dump.u_dsize != 0) {
-		dump_start = START_DATA(dump);
-		dump_size = dump.u_dsize << PAGE_SHIFT;
-		if (!dump_emit(cprm, (void *)dump_start, dump_size))
-			goto end_coredump;
-	}
-	/* Now prepare to dump the stack area */
-	if (dump.u_ssize != 0) {
-		dump_start = START_STACK(dump);
-		dump_size = dump.u_ssize << PAGE_SHIFT;
-		if (!dump_emit(cprm, (void *)dump_start, dump_size))
-			goto end_coredump;
-	}
-end_coredump:
-	set_fs(fs);
-	return has_dumped;
-}
-#endif
 
 /*
  * create_aout_tables() parses the env- and arg-strings in new user
diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index ca9725f18e00..aa0f1e53113f 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -34,92 +34,10 @@
 static int load_aout_binary(struct linux_binprm *);
 static int load_aout_library(struct file*);
 
-#ifdef CONFIG_COREDUMP
-/*
- * Routine writes a core dump image in the current directory.
- * Currently only a stub-function.
- *
- * Note that setuid/setgid files won't make a core-dump if the uid/gid
- * changed due to the set[u|g]id. It's enforced by the "current->mm->dumpable"
- * field, which also makes sure the core-dumps won't be recursive if the
- * dumping of the process results in another error..
- */
-static int aout_core_dump(struct coredump_params *cprm)
-{
-	mm_segment_t fs;
-	int has_dumped = 0;
-	void __user *dump_start;
-	int dump_size;
-	struct user dump;
-#ifdef __alpha__
-#       define START_DATA(u)	((void __user *)u.start_data)
-#else
-#	define START_DATA(u)	((void __user *)((u.u_tsize << PAGE_SHIFT) + \
-				 u.start_code))
-#endif
-#       define START_STACK(u)   ((void __user *)u.start_stack)
-
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-	has_dumped = 1;
-       	strncpy(dump.u_comm, current->comm, sizeof(dump.u_comm));
-	dump.u_ar0 = offsetof(struct user, regs);
-	dump.signal = cprm->siginfo->si_signo;
-	aout_dump_thread(cprm->regs, &dump);
-
-/* If the size of the dump file exceeds the rlimit, then see what would happen
-   if we wrote the stack, but not the data area.  */
-	if ((dump.u_dsize + dump.u_ssize+1) * PAGE_SIZE > cprm->limit)
-		dump.u_dsize = 0;
-
-/* Make sure we have enough room to write the stack and data areas. */
-	if ((dump.u_ssize + 1) * PAGE_SIZE > cprm->limit)
-		dump.u_ssize = 0;
-
-/* make sure we actually have a data and stack area to dump */
-	set_fs(USER_DS);
-	if (!access_ok(START_DATA(dump), dump.u_dsize << PAGE_SHIFT))
-		dump.u_dsize = 0;
-	if (!access_ok(START_STACK(dump), dump.u_ssize << PAGE_SHIFT))
-		dump.u_ssize = 0;
-
-	set_fs(KERNEL_DS);
-/* struct user */
-	if (!dump_emit(cprm, &dump, sizeof(dump)))
-		goto end_coredump;
-/* Now dump all of the user data.  Include malloced stuff as well */
-	if (!dump_skip(cprm, PAGE_SIZE - sizeof(dump)))
-		goto end_coredump;
-/* now we start writing out the user space info */
-	set_fs(USER_DS);
-/* Dump the data area */
-	if (dump.u_dsize != 0) {
-		dump_start = START_DATA(dump);
-		dump_size = dump.u_dsize << PAGE_SHIFT;
-		if (!dump_emit(cprm, dump_start, dump_size))
-			goto end_coredump;
-	}
-/* Now prepare to dump the stack area */
-	if (dump.u_ssize != 0) {
-		dump_start = START_STACK(dump);
-		dump_size = dump.u_ssize << PAGE_SHIFT;
-		if (!dump_emit(cprm, dump_start, dump_size))
-			goto end_coredump;
-	}
-end_coredump:
-	set_fs(fs);
-	return has_dumped;
-}
-#else
-#define aout_core_dump NULL
-#endif
-
 static struct linux_binfmt aout_format = {
 	.module		= THIS_MODULE,
 	.load_binary	= load_aout_binary,
 	.load_shlib	= load_aout_library,
-	.core_dump	= aout_core_dump,
-	.min_coredump	= PAGE_SIZE
 };
 
 #define BAD_ADDR(x)	((unsigned long)(x) >= TASK_SIZE)