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

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Date:   Mon, 10 Apr 2017 15:41:45 +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 Mon, 10 Apr 2017, Thomas Gleixner wrote:

> 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.

It's ways simpler. Patch below.

Thanks,

	tglx

--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -287,7 +287,7 @@ struct task_struct;
 
 #define	ARCH_DLINFO_IA32						\
 do {									\
-	if (vdso32_enabled) {						\
+	if (VDSO_CURRENT_BASE) {					\
 		NEW_AUX_ENT(AT_SYSINFO,	VDSO_ENTRY);			\
 		NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE);	\
 	}								\