linux-kernel - Re: [PATCH] x86/vdso: ensure vdso32_enabled gets set to valid values only

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Date:   Mon, 10 Apr 2017 15:13:59 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mathias Krause <minipli@...glemail.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH] x86/vdso: ensure vdso32_enabled gets set to valid values
 only

On Wed, 5 Apr 2017, Mathias Krause wrote:
> @@ -62,13 +64,18 @@ int __init sysenter_setup(void)
>  /* Register vsyscall32 into the ABI table */
>  #include <linux/sysctl.h>
>  
> +static const int zero;
> +static const int one = 1;
> +
>  static struct ctl_table abi_table2[] = {
>  	{
>  		.procname	= "vsyscall32",
>  		.data		= &vdso32_enabled,
>  		.maxlen		= sizeof(int),
>  		.mode		= 0644,
> -		.proc_handler	= proc_dointvec
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= (int *)&zero,
> +		.extra2		= (int *)&one,

This is still bustable. Let's start with: vdso32_enabled = false

    arch_setup_additional_pages()
	--> No mapping

					sysctl.vsysscall32()
					  --> vdso32_enabled = true

    create_elf_tables()
	if (vdso32_enabled) {
	   --> Add VDSO entry with NULL pointer

The vdso map code needs to store a flag in current which can be checked in
ARCH_DLINFO_IA32.

Thanks,

	tglx