linux-kernel - Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix

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Message-ID: <20150324191556.GA11571@pd.tnic>
Date:	Tue, 24 Mar 2015 20:15:56 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Hector Marco-Gisbert <hecmargi@....es>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan-Simon <dl9pf@....de>, linux-fsdevel@...r.kernel.org,
	Ismael Ripoll <iripoll@...ca.upv.es>
Subject: Re: [PATCH] mm/x86: AMD Bulldozer ASLR fix

On Tue, Mar 24, 2015 at 07:00:48PM +0100, Hector Marco-Gisbert wrote:
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 15c5df9..a693d54 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -5,6 +5,7 @@
>  
>  #include <linux/io.h>
>  #include <linux/sched.h>
> +#include <linux/random.h>
>  #include <asm/processor.h>
>  #include <asm/apic.h>
>  #include <asm/cpu.h>
> @@ -18,6 +19,8 @@
>  
>  #include "cpu.h"
>  
> +unsigned long rnd_bulldozer_bits = 0;
> +
>  static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
>  {
>  	u32 gprs[8] = { 0 };
> @@ -488,6 +491,8 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
>  
>  		va_align.mask	  = (upperbit - 1) & PAGE_MASK;
>  		va_align.flags    = ALIGN_VA_32 | ALIGN_VA_64;
> +		/* A random value per boot for bits 12,13 and 14 */
> +		rnd_bulldozer_bits = get_random_int() & va_align.mask;

Hmm, this should be done differently:

va_align should have a ->bits member which gets ORed in into the hole
made my va_align.mask...

>  	}
>  }
>  
> diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
> index 30277e2..5b8ad01 100644
> --- a/arch/x86/kernel/sys_x86_64.c
> +++ b/arch/x86/kernel/sys_x86_64.c
> @@ -18,6 +18,7 @@
>  
>  #include <asm/ia32.h>
>  #include <asm/syscalls.h>
> +#include <asm/amd_15h.h>
>  
>  /*
>   * Align a virtual address to avoid aliasing in the I$ on AMD F15h.
> @@ -34,10 +35,16 @@ static unsigned long get_align_mask(void)
>  	return va_align.mask;
>  }
>  
> +static unsigned long get_bulldozer_bits(void){
> +
> +	return rnd_bulldozer_bits & get_align_mask();
> +}
> +
>  unsigned long align_vdso_addr(unsigned long addr)
>  {
>  	unsigned long align_mask = get_align_mask();
> -	return (addr + align_mask) & ~align_mask;
> +	addr = (addr + align_mask) & ~align_mask;
> +	return addr | get_bulldozer_bits();
>  }
>  
>  static int __init control_va_addr_alignment(char *str)
> @@ -137,7 +144,10 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
>  	info.high_limit = end;
>  	info.align_mask = filp ? get_align_mask() : 0;

	info.align_bits = get_align_bits() : 0;

>  	info.align_offset = pgoff << PAGE_SHIFT;
> -	return vm_unmapped_area(&info);
> +	addr = vm_unmapped_area(&info);
> +	if (!(addr & ~PAGE_MASK))
> +		return filp ? (addr|get_bulldozer_bits()) : addr;
> +	return addr;
>  }
>  
>  unsigned long
> @@ -178,7 +188,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
>  	info.align_offset = pgoff << PAGE_SHIFT;
>  	addr = vm_unmapped_area(&info);
>  	if (!(addr & ~PAGE_MASK))
> -		return addr;
> +		return filp ? (addr|get_bulldozer_bits()) : addr;

Ditto.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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