Re: + fully-honor-vdso_enabled.patch added to -mm tree

[Oleg Nesterov <oleg@tv-sign.ru>]

John Reiser wrote:
>
> --- a/arch/i386/kernel/sysenter.c~fully-honor-vdso_enabled
> +++ a/arch/i386/kernel/sysenter.c
> @@ -22,6 +22,8 @@
>  #include <asm/msr.h>
>  #include <asm/pgtable.h>
>  #include <asm/unistd.h>
> +#include <asm/a.out.h>
> +#include <asm/mman.h>
>
>  /*
>   * Should the kernel map a VDSO page into processes and pass its
> @@ -105,10 +107,25 @@ int arch_setup_additional_pages(struct l
>  {
>  	struct mm_struct *mm = current->mm;
>  	unsigned long addr;
> +	unsigned long flags;
>  	int ret;
>
> +	switch (vdso_enabled) {
> +	case 0:  /* none */
> +		return 0;

This means we don't initialize mm->context.vdso and ->sysenter_return.

Is it ok? For example, setup_rt_frame() uses VDSO_SYM(&__kernel_rt_sigreturn),
sysenter_past_esp pushes ->sysenter_return on stack.

Note also that load_elf_binary does

	arch_setup_additional_pages()
	create_elf_tables()

, looks like application can crash after exec if vdso_enabled changes from 0
to 1 in between.

Could you please explain if I missed something?

Oleg.