linux-kernel - Re: [PATCH 2/6] exec: simplify the compat syscall handling

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Message-ID: <20200615141239.GA12951@lst.de>
Date:   Mon, 15 Jun 2020 16:12:39 +0200
From:   Christoph Hellwig <hch@....de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] exec: simplify the compat syscall handling

On Mon, Jun 15, 2020 at 03:31:35PM +0200, Arnd Bergmann wrote:
> >  #ifdef CONFIG_COMPAT
> > -       if (unlikely(argv.is_compat)) {
> > +       if (in_compat_syscall()) {
> > +               const compat_uptr_t __user *compat_argv =
> > +                       compat_ptr((unsigned long)argv);
> >                 compat_uptr_t compat;
> >
> > -               if (get_user(compat, argv.ptr.compat + nr))
> > +               if (get_user(compat, compat_argv + nr))
> >                         return ERR_PTR(-EFAULT);
> >
> >                 return compat_ptr(compat);
> >         }
> >  #endif
> 
> I would expect that the "#ifdef CONFIG_COMPAT" can be removed
> now, since compat_ptr() and in_compat_syscall() are now defined
> unconditionally. I have not tried that though.

True, I'll give it a spin.

> > +/*
> > + * x32 syscalls are listed in the same table as x86_64 ones, so we need to
> > + * define compat syscalls that are exactly the same as the native version for
> > + * the syscall table machinery to work.  Sigh..
> > + */
> > +#ifdef CONFIG_X86_X32
> >  COMPAT_SYSCALL_DEFINE3(execve, const char __user *, filename,
> > -       const compat_uptr_t __user *, argv,
> > -       const compat_uptr_t __user *, envp)
> > +                      const char __user *const __user *, argv,
> > +                      const char __user *const __user *, envp)
> >  {
> > -       return do_compat_execve(AT_FDCWD, getname(filename), argv, envp, 0);
> > +       return do_execveat(AT_FDCWD, getname(filename), argv, envp, 0, NULL);
> >  }
> 
> Maybe move it to arch/x86/kernel/process_64.c or arch/x86/entry/syscall_x32.c
> to keep it out of the common code if this is needed.

I'd rather keep it in common code as that allows all the low-level
exec stuff to be marked static, and avoid us growing new pointless
compat variants through copy and paste.
smart compiler to d

> I don't really understand
> the comment, why can't this just use this?

That errors out with:

ld: arch/x86/entry/syscall_x32.o:(.rodata+0x1040): undefined reference to
`__x32_sys_execve'
ld: arch/x86/entry/syscall_x32.o:(.rodata+0x1108): undefined reference to
`__x32_sys_execveat'
make: *** [Makefile:1139: vmlinux] Error 1