linux-kernel - Re: [PATCH v2 7/8] x86/vsyscall: Add __ro_after

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Message-ID: <201906271030.A5C7F4A202@keescook>
Date:   Thu, 27 Jun 2019 10:30:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Jann Horn <jannh@...gle.com>, Borislav Petkov <bp@...en8.de>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 7/8] x86/vsyscall: Add __ro_after_init to global
 variables

On Wed, Jun 26, 2019 at 09:45:08PM -0700, Andy Lutomirski wrote:
> The vDSO is only configurable by command-line options, so make its
> global variables __ro_after_init.  This seems highly unlikely to
> ever stop an exploit, but I think it's nice anyway.
> 
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index 9c58ab807aeb..07003f3f1bfc 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -42,7 +42,7 @@
>  #define CREATE_TRACE_POINTS
>  #include "vsyscall_trace.h"
>  
> -static enum { EMULATE, XONLY, NONE } vsyscall_mode =
> +static enum { EMULATE, XONLY, NONE } vsyscall_mode __ro_after_init =
>  #ifdef CONFIG_LEGACY_VSYSCALL_NONE
>  	NONE;
>  #elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
> @@ -305,7 +305,7 @@ static const char *gate_vma_name(struct vm_area_struct *vma)
>  static const struct vm_operations_struct gate_vma_ops = {
>  	.name = gate_vma_name,
>  };
> -static struct vm_area_struct gate_vma = {
> +static struct vm_area_struct gate_vma __ro_after_init = {
>  	.vm_start	= VSYSCALL_ADDR,
>  	.vm_end		= VSYSCALL_ADDR + PAGE_SIZE,
>  	.vm_page_prot	= PAGE_READONLY_EXEC,
> -- 
> 2.21.0
> 

-- 
Kees Cook