linux-kernel - Re: [PATCH v3] x86/mm/init_32: Stop printing the virtual memory layout

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Message-ID: <202003050927.530CC2D6DD@keescook>
Date:   Thu, 5 Mar 2020 09:28:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Tobin C . Harding" <me@...in.cc>, Tycho Andersen <tycho@...ho.ws>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        kernel-hardening@...ts.openwall.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86/mm/init_32: Stop printing the virtual memory
 layout

On Thu, Mar 05, 2020 at 10:01:52AM -0500, Arvind Sankar wrote:
> For security, don't display the kernel's virtual memory layout.
> 
> Kees Cook points out:
> "These have been entirely removed on other architectures, so let's
> just do the same for ia32 and remove it unconditionally."
> 
> 071929dbdd86 ("arm64: Stop printing the virtual memory layout")
> 1c31d4e96b8c ("ARM: 8820/1: mm: Stop printing the virtual memory layout")
> 31833332f798 ("m68k/mm: Stop printing the virtual memory layout")
> fd8d0ca25631 ("parisc: Hide virtual kernel memory layout")
> adb1fe9ae2ee ("mm/page_alloc: Remove kernel address exposure in free_reserved_area()")
> 
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>

Thanks!

(*randomly choosing an x86 maintainer to aim this patch at; hi Thomas!*)

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

-Kees

> ---
>  arch/x86/mm/init_32.c | 38 --------------------------------------
>  1 file changed, 38 deletions(-)
> 
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 23df4885bbed..8ae0272c1c51 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -788,44 +788,6 @@ void __init mem_init(void)
>  	x86_init.hyper.init_after_bootmem();
>  
>  	mem_init_print_info(NULL);
> -	printk(KERN_INFO "virtual kernel memory layout:\n"
> -		"    fixmap  : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> -		"  cpu_entry : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> -#ifdef CONFIG_HIGHMEM
> -		"    pkmap   : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> -#endif
> -		"    vmalloc : 0x%08lx - 0x%08lx   (%4ld MB)\n"
> -		"    lowmem  : 0x%08lx - 0x%08lx   (%4ld MB)\n"
> -		"      .init : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> -		"      .data : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> -		"      .text : 0x%08lx - 0x%08lx   (%4ld kB)\n",
> -		FIXADDR_START, FIXADDR_TOP,
> -		(FIXADDR_TOP - FIXADDR_START) >> 10,
> -
> -		CPU_ENTRY_AREA_BASE,
> -		CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE,
> -		CPU_ENTRY_AREA_MAP_SIZE >> 10,
> -
> -#ifdef CONFIG_HIGHMEM
> -		PKMAP_BASE, PKMAP_BASE+LAST_PKMAP*PAGE_SIZE,
> -		(LAST_PKMAP*PAGE_SIZE) >> 10,
> -#endif
> -
> -		VMALLOC_START, VMALLOC_END,
> -		(VMALLOC_END - VMALLOC_START) >> 20,
> -
> -		(unsigned long)__va(0), (unsigned long)high_memory,
> -		((unsigned long)high_memory - (unsigned long)__va(0)) >> 20,
> -
> -		(unsigned long)&__init_begin, (unsigned long)&__init_end,
> -		((unsigned long)&__init_end -
> -		 (unsigned long)&__init_begin) >> 10,
> -
> -		(unsigned long)&_etext, (unsigned long)&_edata,
> -		((unsigned long)&_edata - (unsigned long)&_etext) >> 10,
> -
> -		(unsigned long)&_text, (unsigned long)&_etext,
> -		((unsigned long)&_etext - (unsigned long)&_text) >> 10);
>  
>  	/*
>  	 * Check boundaries twice: Some fundamental inconsistencies can
> -- 
> 2.24.1
> 

-- 
Kees Cook