Message-ID: <0b31b1d3-852d-6cab-82ae-5eecaec05679@theinnocuous.com>
Date:   Sat, 12 Mar 2022 18:06:26 +0000
From:   James Jones <linux@...innocuous.com>
To:     bp@...en8.de, keescook@...omium.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Remove a.out support

On 3/12/22 9:54 AM, James Jones wrote:
>> From: Borislav Petkov <bp@...e.de>
>>
>> Commit
>>
>>    eac616557050 ("x86: Deprecate a.out support")
>>
>> deprecated a.out support with the promise to remove it a couple of
>> releases later. That commit landed in v5.1.
>>
>> Now it is more than a couple of releases later, no one has complained so
>> remove it.
>
> Sorry for taking so long to complain, but I have been meaning to note
> that I and a few others are still using a.out. I saw it go by in my
> morning Google news skim that this went in, and figured it was now or
> never. The use case is running an old set of tools to build programs for
> the Atari Jaguar. Namely, Atari's assembler (mac) and linker (aln). The
> alternative is running windows versions in dosbox, or using some
> replacements that have been developed based on an even older,
> less-featureful version of the source code for mac and aln, but which
> still haven't managed to add back in all the features needed to build
> some programs or use the Atari debugging tools (Also available in a.out
> only).
>
> I've been running with a few local patches to fix the a.out build and
> add the Kconfig options back for the last year or so to enable this on a
> few of my machines, and it's been working fine. I know of at least one
> other person doing this. If the code itself and supporting
> syscalls/other code go away though, it'll probably become impractical.
> If others are open to it, I can share my small local patches along with
> a revert of this change. I'd also like to ask whether much is gained by
> deleting this code as far as reducing maintenance burden. It has
> survived nearly untouched since the deprecation notice and still works
> modulo a broken preprocessor macro in fs/exec.c.
>
> For the curious, or if anyone wants proof I'm not making this up and
> really do spend time on these things, my amalgamation of Jaguar tools &
> docs, including copies of the old mac and aln a.out binaries, is
> available here:
>
> https://github.com/cubanismo/jaguar-sdk

Apologies, fixing x86 maintainer alias address.

> Thanks,
> -James
>
>> Signed-off-by: Borislav Petkov <bp@...e.de>
>> ---
>>   arch/x86/Kconfig          |   7 -
>>   arch/x86/ia32/Makefile    |   2 -
>>   arch/x86/ia32/ia32_aout.c | 325 --------------------------------------
>>   3 files changed, 334 deletions(-)
>>   delete mode 100644 arch/x86/ia32/ia32_aout.c
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 976dd6b532bf..6f3d63dbbddf 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2835,13 +2835,6 @@ config IA32_EMULATION
>>   	  64-bit kernel. You should likely turn this on, unless you're
>>   	  100% sure that you don't have any 32-bit programs left.
>>
>> -config IA32_AOUT
>> -	tristate "IA32 a.out support"
>> -	depends on IA32_EMULATION
>> -	depends on BROKEN
>> -	help
>> -	  Support old a.out binaries in the 32bit emulation.
>> -
>>   config X86_X32
>>   	bool "x32 ABI for 64-bit mode"
>>   	depends on X86_64
>> diff --git a/arch/x86/ia32/Makefile b/arch/x86/ia32/Makefile
>> index 8e4d0391ff6c..e481056698de 100644
>> --- a/arch/x86/ia32/Makefile
>> +++ b/arch/x86/ia32/Makefile
>> @@ -5,7 +5,5 @@
>>
>>   obj-$(CONFIG_IA32_EMULATION) := ia32_signal.o
>>
>> -obj-$(CONFIG_IA32_AOUT) += ia32_aout.o
>> -
>>   audit-class-$(CONFIG_AUDIT) := audit.o
>>   obj-$(CONFIG_IA32_EMULATION) += $(audit-class-y)
>> diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
>> deleted file mode 100644
>> index 9bd15241fadb..000000000000
>> --- a/arch/x86/ia32/ia32_aout.c
>> +++ /dev/null
>> @@ -1,325 +0,0 @@
>> -// SPDX-License-Identifier: GPL-2.0-only
>> -/*
>> - *  a.out loader for x86-64
>> - *
>> - *  Copyright (C) 1991, 1992, 1996  Linus Torvalds
>> - *  Hacked together by Andi Kleen
>> - */
>> -
>> -#include <linux/module.h>
>> -
>> -#include <linux/time.h>
>> -#include <linux/kernel.h>
>> -#include <linux/mm.h>
>> -#include <linux/mman.h>
>> -#include <linux/a.out.h>
>> -#include <linux/errno.h>
>> -#include <linux/signal.h>
>> -#include <linux/string.h>
>> -#include <linux/fs.h>
>> -#include <linux/file.h>
>> -#include <linux/stat.h>
>> -#include <linux/fcntl.h>
>> -#include <linux/ptrace.h>
>> -#include <linux/user.h>
>> -#include <linux/binfmts.h>
>> -#include <linux/personality.h>
>> -#include <linux/init.h>
>> -#include <linux/jiffies.h>
>> -#include <linux/perf_event.h>
>> -#include <linux/sched/task_stack.h>
>> -
>> -#include <linux/uaccess.h>
>> -#include <asm/cacheflush.h>
>> -#include <asm/user32.h>
>> -#include <asm/ia32.h>
>> -
>> -#undef WARN_OLD
>> -
>> -static int load_aout_binary(struct linux_binprm *);
>> -static int load_aout_library(struct file *);
>> -
>> -static struct linux_binfmt aout_format = {
>> -	.module		= THIS_MODULE,
>> -	.load_binary	= load_aout_binary,
>> -	.load_shlib	= load_aout_library,
>> -};
>> -
>> -static int set_brk(unsigned long start, unsigned long end)
>> -{
>> -	start = PAGE_ALIGN(start);
>> -	end = PAGE_ALIGN(end);
>> -	if (end <= start)
>> -		return 0;
>> -	return vm_brk(start, end - start);
>> -}
>> -
>> -
>> -/*
>> - * create_aout_tables() parses the env- and arg-strings in new user
>> - * memory and creates the pointer tables from them, and puts their
>> - * addresses on the "stack", returning the new stack pointer value.
>> - */
>> -static u32 __user *create_aout_tables(char __user *p, struct linux_binprm *bprm)
>> -{
>> -	u32 __user *argv, *envp, *sp;
>> -	int argc = bprm->argc, envc = bprm->envc;
>> -
>> -	sp = (u32 __user *) ((-(unsigned long)sizeof(u32)) & (unsigned long) p);
>> -	sp -= envc+1;
>> -	envp = sp;
>> -	sp -= argc+1;
>> -	argv = sp;
>> -	put_user((unsigned long) envp, --sp);
>> -	put_user((unsigned long) argv, --sp);
>> -	put_user(argc, --sp);
>> -	current->mm->arg_start = (unsigned long) p;
>> -	while (argc-- > 0) {
>> -		char c;
>> -
>> -		put_user((u32)(unsigned long)p, argv++);
>> -		do {
>> -			get_user(c, p++);
>> -		} while (c);
>> -	}
>> -	put_user(0, argv);
>> -	current->mm->arg_end = current->mm->env_start = (unsigned long) p;
>> -	while (envc-- > 0) {
>> -		char c;
>> -
>> -		put_user((u32)(unsigned long)p, envp++);
>> -		do {
>> -			get_user(c, p++);
>> -		} while (c);
>> -	}
>> -	put_user(0, envp);
>> -	current->mm->env_end = (unsigned long) p;
>> -	return sp;
>> -}
>> -
>> -/*
>> - * These are the functions used to load a.out style executables and shared
>> - * libraries.  There is no binary dependent code anywhere else.
>> - */
>> -static int load_aout_binary(struct linux_binprm *bprm)
>> -{
>> -	unsigned long error, fd_offset, rlim;
>> -	struct pt_regs *regs = current_pt_regs();
>> -	struct exec ex;
>> -	int retval;
>> -
>> -	ex = *((struct exec *) bprm->buf);		/* exec-header */
>> -	if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != OMAGIC &&
>> -	     N_MAGIC(ex) != QMAGIC && N_MAGIC(ex) != NMAGIC) ||
>> -	    N_TRSIZE(ex) || N_DRSIZE(ex) ||
>> -	    i_size_read(file_inode(bprm->file)) <
>> -	    ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
>> -		return -ENOEXEC;
>> -	}
>> -
>> -	fd_offset = N_TXTOFF(ex);
>> -
>> -	/* Check initial limits. This avoids letting people circumvent
>> -	 * size limits imposed on them by creating programs with large
>> -	 * arrays in the data or bss.
>> -	 */
>> -	rlim = rlimit(RLIMIT_DATA);
>> -	if (rlim >= RLIM_INFINITY)
>> -		rlim = ~0;
>> -	if (ex.a_data + ex.a_bss > rlim)
>> -		return -ENOMEM;
>> -
>> -	/* Flush all traces of the currently running executable */
>> -	retval = begin_new_exec(bprm);
>> -	if (retval)
>> -		return retval;
>> -
>> -	/* OK, This is the point of no return */
>> -	set_personality(PER_LINUX);
>> -	set_personality_ia32(false);
>> -
>> -	setup_new_exec(bprm);
>> -
>> -	regs->cs = __USER32_CS;
>> -	regs->r8 = regs->r9 = regs->r10 = regs->r11 = regs->r12 =
>> -		regs->r13 = regs->r14 = regs->r15 = 0;
>> -
>> -	current->mm->end_code = ex.a_text +
>> -		(current->mm->start_code = N_TXTADDR(ex));
>> -	current->mm->end_data = ex.a_data +
>> -		(current->mm->start_data = N_DATADDR(ex));
>> -	current->mm->brk = ex.a_bss +
>> -		(current->mm->start_brk = N_BSSADDR(ex));
>> -
>> -	retval = setup_arg_pages(bprm, IA32_STACK_TOP, EXSTACK_DEFAULT);
>> -	if (retval < 0)
>> -		return retval;
>> -
>> -	if (N_MAGIC(ex) == OMAGIC) {
>> -		unsigned long text_addr, map_size;
>> -
>> -		text_addr = N_TXTADDR(ex);
>> -		map_size = ex.a_text+ex.a_data;
>> -
>> -		error = vm_brk(text_addr & PAGE_MASK, map_size);
>> -
>> -		if (error)
>> -			return error;
>> -
>> -		error = read_code(bprm->file, text_addr, 32,
>> -				  ex.a_text + ex.a_data);
>> -		if ((signed long)error < 0)
>> -			return error;
>> -	} else {
>> -#ifdef WARN_OLD
>> -		static unsigned long error_time, error_time2;
>> -		if ((ex.a_text & 0xfff || ex.a_data & 0xfff) &&
>> -		    (N_MAGIC(ex) != NMAGIC) &&
>> -				time_after(jiffies, error_time2 + 5*HZ)) {
>> -			printk(KERN_NOTICE "executable not page aligned\n");
>> -			error_time2 = jiffies;
>> -		}
>> -
>> -		if ((fd_offset & ~PAGE_MASK) != 0 &&
>> -			    time_after(jiffies, error_time + 5*HZ)) {
>> -			printk(KERN_WARNING
>> -			       "fd_offset is not page aligned. Please convert "
>> -			       "program: %pD\n",
>> -			       bprm->file);
>> -			error_time = jiffies;
>> -		}
>> -#endif
>> -
>> -		if (!bprm->file->f_op->mmap || (fd_offset & ~PAGE_MASK) != 0) {
>> -			error = vm_brk(N_TXTADDR(ex), ex.a_text+ex.a_data);
>> -			if (error)
>> -				return error;
>> -
>> -			read_code(bprm->file, N_TXTADDR(ex), fd_offset,
>> -					ex.a_text+ex.a_data);
>> -			goto beyond_if;
>> -		}
>> -
>> -		error = vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
>> -				PROT_READ | PROT_EXEC,
>> -				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -				fd_offset);
>> -
>> -		if (error != N_TXTADDR(ex))
>> -			return error;
>> -
>> -		error = vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
>> -				PROT_READ | PROT_WRITE | PROT_EXEC,
>> -				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -				fd_offset + ex.a_text);
>> -		if (error != N_DATADDR(ex))
>> -			return error;
>> -	}
>> -
>> -beyond_if:
>> -	error = set_brk(current->mm->start_brk, current->mm->brk);
>> -	if (error)
>> -		return error;
>> -
>> -	set_binfmt(&aout_format);
>> -
>> -	current->mm->start_stack =
>> -		(unsigned long)create_aout_tables((char __user *)bprm->p, bprm);
>> -	/* start thread */
>> -	loadsegment(fs, 0);
>> -	loadsegment(ds, __USER32_DS);
>> -	loadsegment(es, __USER32_DS);
>> -	load_gs_index(0);
>> -	(regs)->ip = ex.a_entry;
>> -	(regs)->sp = current->mm->start_stack;
>> -	(regs)->flags = 0x200;
>> -	(regs)->cs = __USER32_CS;
>> -	(regs)->ss = __USER32_DS;
>> -	regs->r8 = regs->r9 = regs->r10 = regs->r11 =
>> -	regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;
>> -	return 0;
>> -}
>> -
>> -static int load_aout_library(struct file *file)
>> -{
>> -	unsigned long bss, start_addr, len, error;
>> -	int retval;
>> -	struct exec ex;
>> -	loff_t pos = 0;
>> -
>> -	retval = -ENOEXEC;
>> -	error = kernel_read(file, &ex, sizeof(ex), &pos);
>> -	if (error != sizeof(ex))
>> -		goto out;
>> -
>> -	/* We come in here for the regular a.out style of shared libraries */
>> -	if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != QMAGIC) || N_TRSIZE(ex) ||
>> -	    N_DRSIZE(ex) || ((ex.a_entry & 0xfff) && N_MAGIC(ex) == ZMAGIC) ||
>> -	    i_size_read(file_inode(file)) <
>> -	    ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
>> -		goto out;
>> -	}
>> -
>> -	if (N_FLAGS(ex))
>> -		goto out;
>> -
>> -	/* For  QMAGIC, the starting address is 0x20 into the page.  We mask
>> -	   this off to get the starting address for the page */
>> -
>> -	start_addr =  ex.a_entry & 0xfffff000;
>> -
>> -	if ((N_TXTOFF(ex) & ~PAGE_MASK) != 0) {
>> -#ifdef WARN_OLD
>> -		static unsigned long error_time;
>> -		if (time_after(jiffies, error_time + 5*HZ)) {
>> -			printk(KERN_WARNING
>> -			       "N_TXTOFF is not page aligned. Please convert "
>> -			       "library: %pD\n",
>> -			       file);
>> -			error_time = jiffies;
>> -		}
>> -#endif
>> -		retval = vm_brk(start_addr, ex.a_text + ex.a_data + ex.a_bss);
>> -		if (retval)
>> -			goto out;
>> -
>> -		read_code(file, start_addr, N_TXTOFF(ex),
>> -			  ex.a_text + ex.a_data);
>> -		retval = 0;
>> -		goto out;
>> -	}
>> -	/* Now use mmap to map the library into memory. */
>> -	error = vm_mmap(file, start_addr, ex.a_text + ex.a_data,
>> -			PROT_READ | PROT_WRITE | PROT_EXEC,
>> -			MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -			N_TXTOFF(ex));
>> -	retval = error;
>> -	if (error != start_addr)
>> -		goto out;
>> -
>> -	len = PAGE_ALIGN(ex.a_text + ex.a_data);
>> -	bss = ex.a_text + ex.a_data + ex.a_bss;
>> -	if (bss > len) {
>> -		retval = vm_brk(start_addr + len, bss - len);
>> -		if (retval)
>> -			goto out;
>> -	}
>> -	retval = 0;
>> -out:
>> -	return retval;
>> -}
>> -
>> -static int __init init_aout_binfmt(void)
>> -{
>> -	register_binfmt(&aout_format);
>> -	return 0;
>> -}
>> -
>> -static void __exit exit_aout_binfmt(void)
>> -{
>> -	unregister_binfmt(&aout_format);
>> -}
>> -
>> -module_init(init_aout_binfmt);
>> -module_exit(exit_aout_binfmt);
>> -MODULE_LICENSE("GPL");
>> --
>> 2.29.2
>

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