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

Christoph Hellwig
2020-06-15T14:12:39Z

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