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Date:   Sat, 12 Mar 2022 18:06:26 +0000
To:     bp@alien8.de, keescook@chromium.org
From:   James Jones <linux@theinnocuous.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org
Reply-To: James Jones <linux@theinnocuous.com>
Subject: Re: [PATCH] x86: Remove a.out support
Message-ID: <0b31b1d3-852d-6cab-82ae-5eecaec05679@theinnocuous.com>
In-Reply-To: <4c449fab-8135-5057-7d2c-7b948ce130cc@theinnocuous.com>
References: <4c449fab-8135-5057-7d2c-7b948ce130cc@theinnocuous.com>
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On 3/12/22 9:54 AM, James Jones wrote:
>> From: Borislav Petkov <bp@suse.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@suse.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
>>   =09  64-bit kernel. You should likely turn this on, unless you're
>>   =09  100% sure that you don't have any 32-bit programs left.
>>
>> -config IA32_AOUT
>> -=09tristate "IA32 a.out support"
>> -=09depends on IA32_EMULATION
>> -=09depends on BROKEN
>> -=09help
>> -=09  Support old a.out binaries in the 32bit emulation.
>> -
>>   config X86_X32
>>   =09bool "x32 ABI for 64-bit mode"
>>   =09depends 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-$(CONFIG_IA32_EMULATION) :=3D ia32_signal.o
>>
>> -obj-$(CONFIG_IA32_AOUT) +=3D ia32_aout.o
>> -
>>   audit-class-$(CONFIG_AUDIT) :=3D audit.o
>>   obj-$(CONFIG_IA32_EMULATION) +=3D $(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 =3D {
>> -=09.module=09=09=3D THIS_MODULE,
>> -=09.load_binary=09=3D load_aout_binary,
>> -=09.load_shlib=09=3D load_aout_library,
>> -};
>> -
>> -static int set_brk(unsigned long start, unsigned long end)
>> -{
>> -=09start =3D PAGE_ALIGN(start);
>> -=09end =3D PAGE_ALIGN(end);
>> -=09if (end <=3D start)
>> -=09=09return 0;
>> -=09return 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_binp=
rm *bprm)
>> -{
>> -=09u32 __user *argv, *envp, *sp;
>> -=09int argc =3D bprm->argc, envc =3D bprm->envc;
>> -
>> -=09sp =3D (u32 __user *) ((-(unsigned long)sizeof(u32)) & (unsigned lon=
g) p);
>> -=09sp -=3D envc+1;
>> -=09envp =3D sp;
>> -=09sp -=3D argc+1;
>> -=09argv =3D sp;
>> -=09put_user((unsigned long) envp, --sp);
>> -=09put_user((unsigned long) argv, --sp);
>> -=09put_user(argc, --sp);
>> -=09current->mm->arg_start =3D (unsigned long) p;
>> -=09while (argc-- > 0) {
>> -=09=09char c;
>> -
>> -=09=09put_user((u32)(unsigned long)p, argv++);
>> -=09=09do {
>> -=09=09=09get_user(c, p++);
>> -=09=09} while (c);
>> -=09}
>> -=09put_user(0, argv);
>> -=09current->mm->arg_end =3D current->mm->env_start =3D (unsigned long) =
p;
>> -=09while (envc-- > 0) {
>> -=09=09char c;
>> -
>> -=09=09put_user((u32)(unsigned long)p, envp++);
>> -=09=09do {
>> -=09=09=09get_user(c, p++);
>> -=09=09} while (c);
>> -=09}
>> -=09put_user(0, envp);
>> -=09current->mm->env_end =3D (unsigned long) p;
>> -=09return sp;
>> -}
>> -
>> -/*
>> - * These are the functions used to load a.out style executables and sha=
red
>> - * libraries.  There is no binary dependent code anywhere else.
>> - */
>> -static int load_aout_binary(struct linux_binprm *bprm)
>> -{
>> -=09unsigned long error, fd_offset, rlim;
>> -=09struct pt_regs *regs =3D current_pt_regs();
>> -=09struct exec ex;
>> -=09int retval;
>> -
>> -=09ex =3D *((struct exec *) bprm->buf);=09=09/* exec-header */
>> -=09if ((N_MAGIC(ex) !=3D ZMAGIC && N_MAGIC(ex) !=3D OMAGIC &&
>> -=09     N_MAGIC(ex) !=3D QMAGIC && N_MAGIC(ex) !=3D NMAGIC) ||
>> -=09    N_TRSIZE(ex) || N_DRSIZE(ex) ||
>> -=09    i_size_read(file_inode(bprm->file)) <
>> -=09    ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
>> -=09=09return -ENOEXEC;
>> -=09}
>> -
>> -=09fd_offset =3D N_TXTOFF(ex);
>> -
>> -=09/* Check initial limits. This avoids letting people circumvent
>> -=09 * size limits imposed on them by creating programs with large
>> -=09 * arrays in the data or bss.
>> -=09 */
>> -=09rlim =3D rlimit(RLIMIT_DATA);
>> -=09if (rlim >=3D RLIM_INFINITY)
>> -=09=09rlim =3D ~0;
>> -=09if (ex.a_data + ex.a_bss > rlim)
>> -=09=09return -ENOMEM;
>> -
>> -=09/* Flush all traces of the currently running executable */
>> -=09retval =3D begin_new_exec(bprm);
>> -=09if (retval)
>> -=09=09return retval;
>> -
>> -=09/* OK, This is the point of no return */
>> -=09set_personality(PER_LINUX);
>> -=09set_personality_ia32(false);
>> -
>> -=09setup_new_exec(bprm);
>> -
>> -=09regs->cs =3D __USER32_CS;
>> -=09regs->r8 =3D regs->r9 =3D regs->r10 =3D regs->r11 =3D regs->r12 =3D
>> -=09=09regs->r13 =3D regs->r14 =3D regs->r15 =3D 0;
>> -
>> -=09current->mm->end_code =3D ex.a_text +
>> -=09=09(current->mm->start_code =3D N_TXTADDR(ex));
>> -=09current->mm->end_data =3D ex.a_data +
>> -=09=09(current->mm->start_data =3D N_DATADDR(ex));
>> -=09current->mm->brk =3D ex.a_bss +
>> -=09=09(current->mm->start_brk =3D N_BSSADDR(ex));
>> -
>> -=09retval =3D setup_arg_pages(bprm, IA32_STACK_TOP, EXSTACK_DEFAULT);
>> -=09if (retval < 0)
>> -=09=09return retval;
>> -
>> -=09if (N_MAGIC(ex) =3D=3D OMAGIC) {
>> -=09=09unsigned long text_addr, map_size;
>> -
>> -=09=09text_addr =3D N_TXTADDR(ex);
>> -=09=09map_size =3D ex.a_text+ex.a_data;
>> -
>> -=09=09error =3D vm_brk(text_addr & PAGE_MASK, map_size);
>> -
>> -=09=09if (error)
>> -=09=09=09return error;
>> -
>> -=09=09error =3D read_code(bprm->file, text_addr, 32,
>> -=09=09=09=09  ex.a_text + ex.a_data);
>> -=09=09if ((signed long)error < 0)
>> -=09=09=09return error;
>> -=09} else {
>> -#ifdef WARN_OLD
>> -=09=09static unsigned long error_time, error_time2;
>> -=09=09if ((ex.a_text & 0xfff || ex.a_data & 0xfff) &&
>> -=09=09    (N_MAGIC(ex) !=3D NMAGIC) &&
>> -=09=09=09=09time_after(jiffies, error_time2 + 5*HZ)) {
>> -=09=09=09printk(KERN_NOTICE "executable not page aligned\n");
>> -=09=09=09error_time2 =3D jiffies;
>> -=09=09}
>> -
>> -=09=09if ((fd_offset & ~PAGE_MASK) !=3D 0 &&
>> -=09=09=09    time_after(jiffies, error_time + 5*HZ)) {
>> -=09=09=09printk(KERN_WARNING
>> -=09=09=09       "fd_offset is not page aligned. Please convert "
>> -=09=09=09       "program: %pD\n",
>> -=09=09=09       bprm->file);
>> -=09=09=09error_time =3D jiffies;
>> -=09=09}
>> -#endif
>> -
>> -=09=09if (!bprm->file->f_op->mmap || (fd_offset & ~PAGE_MASK) !=3D 0) {
>> -=09=09=09error =3D vm_brk(N_TXTADDR(ex), ex.a_text+ex.a_data);
>> -=09=09=09if (error)
>> -=09=09=09=09return error;
>> -
>> -=09=09=09read_code(bprm->file, N_TXTADDR(ex), fd_offset,
>> -=09=09=09=09=09ex.a_text+ex.a_data);
>> -=09=09=09goto beyond_if;
>> -=09=09}
>> -
>> -=09=09error =3D vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
>> -=09=09=09=09PROT_READ | PROT_EXEC,
>> -=09=09=09=09MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -=09=09=09=09fd_offset);
>> -
>> -=09=09if (error !=3D N_TXTADDR(ex))
>> -=09=09=09return error;
>> -
>> -=09=09error =3D vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
>> -=09=09=09=09PROT_READ | PROT_WRITE | PROT_EXEC,
>> -=09=09=09=09MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -=09=09=09=09fd_offset + ex.a_text);
>> -=09=09if (error !=3D N_DATADDR(ex))
>> -=09=09=09return error;
>> -=09}
>> -
>> -beyond_if:
>> -=09error =3D set_brk(current->mm->start_brk, current->mm->brk);
>> -=09if (error)
>> -=09=09return error;
>> -
>> -=09set_binfmt(&aout_format);
>> -
>> -=09current->mm->start_stack =3D
>> -=09=09(unsigned long)create_aout_tables((char __user *)bprm->p, bprm);
>> -=09/* start thread */
>> -=09loadsegment(fs, 0);
>> -=09loadsegment(ds, __USER32_DS);
>> -=09loadsegment(es, __USER32_DS);
>> -=09load_gs_index(0);
>> -=09(regs)->ip =3D ex.a_entry;
>> -=09(regs)->sp =3D current->mm->start_stack;
>> -=09(regs)->flags =3D 0x200;
>> -=09(regs)->cs =3D __USER32_CS;
>> -=09(regs)->ss =3D __USER32_DS;
>> -=09regs->r8 =3D regs->r9 =3D regs->r10 =3D regs->r11 =3D
>> -=09regs->r12 =3D regs->r13 =3D regs->r14 =3D regs->r15 =3D 0;
>> -=09return 0;
>> -}
>> -
>> -static int load_aout_library(struct file *file)
>> -{
>> -=09unsigned long bss, start_addr, len, error;
>> -=09int retval;
>> -=09struct exec ex;
>> -=09loff_t pos =3D 0;
>> -
>> -=09retval =3D -ENOEXEC;
>> -=09error =3D kernel_read(file, &ex, sizeof(ex), &pos);
>> -=09if (error !=3D sizeof(ex))
>> -=09=09goto out;
>> -
>> -=09/* We come in here for the regular a.out style of shared libraries *=
/
>> -=09if ((N_MAGIC(ex) !=3D ZMAGIC && N_MAGIC(ex) !=3D QMAGIC) || N_TRSIZE=
(ex) ||
>> -=09    N_DRSIZE(ex) || ((ex.a_entry & 0xfff) && N_MAGIC(ex) =3D=3D ZMAG=
IC) ||
>> -=09    i_size_read(file_inode(file)) <
>> -=09    ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
>> -=09=09goto out;
>> -=09}
>> -
>> -=09if (N_FLAGS(ex))
>> -=09=09goto out;
>> -
>> -=09/* For  QMAGIC, the starting address is 0x20 into the page.  We mask
>> -=09   this off to get the starting address for the page */
>> -
>> -=09start_addr =3D  ex.a_entry & 0xfffff000;
>> -
>> -=09if ((N_TXTOFF(ex) & ~PAGE_MASK) !=3D 0) {
>> -#ifdef WARN_OLD
>> -=09=09static unsigned long error_time;
>> -=09=09if (time_after(jiffies, error_time + 5*HZ)) {
>> -=09=09=09printk(KERN_WARNING
>> -=09=09=09       "N_TXTOFF is not page aligned. Please convert "
>> -=09=09=09       "library: %pD\n",
>> -=09=09=09       file);
>> -=09=09=09error_time =3D jiffies;
>> -=09=09}
>> -#endif
>> -=09=09retval =3D vm_brk(start_addr, ex.a_text + ex.a_data + ex.a_bss);
>> -=09=09if (retval)
>> -=09=09=09goto out;
>> -
>> -=09=09read_code(file, start_addr, N_TXTOFF(ex),
>> -=09=09=09  ex.a_text + ex.a_data);
>> -=09=09retval =3D 0;
>> -=09=09goto out;
>> -=09}
>> -=09/* Now use mmap to map the library into memory. */
>> -=09error =3D vm_mmap(file, start_addr, ex.a_text + ex.a_data,
>> -=09=09=09PROT_READ | PROT_WRITE | PROT_EXEC,
>> -=09=09=09MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>> -=09=09=09N_TXTOFF(ex));
>> -=09retval =3D error;
>> -=09if (error !=3D start_addr)
>> -=09=09goto out;
>> -
>> -=09len =3D PAGE_ALIGN(ex.a_text + ex.a_data);
>> -=09bss =3D ex.a_text + ex.a_data + ex.a_bss;
>> -=09if (bss > len) {
>> -=09=09retval =3D vm_brk(start_addr + len, bss - len);
>> -=09=09if (retval)
>> -=09=09=09goto out;
>> -=09}
>> -=09retval =3D 0;
>> -out:
>> -=09return retval;
>> -}
>> -
>> -static int __init init_aout_binfmt(void)
>> -{
>> -=09register_binfmt(&aout_format);
>> -=09return 0;
>> -}
>> -
>> -static void __exit exit_aout_binfmt(void)
>> -{
>> -=09unregister_binfmt(&aout_format);
>> -}
>> -
>> -module_init(init_aout_binfmt);
>> -module_exit(exit_aout_binfmt);
>> -MODULE_LICENSE("GPL");
>> --
>> 2.29.2
>