[linux-yocto] [PATCH 1/3] x86, kaslr: randomize module base load address

[Paul Gortmaker]

On 14-07-28 10:58 PM, Yang Shi wrote:
> From: Kees Cook <keescook at chromium.org>
> 
> commit e2b32e6785138d92d2a40e0d0473575c8c7310a2 upstream

Unless I missed it, it would be nice if these 3 patches had a 0/3
that had some context about what they are fixing and why they
are selected for cherry pick.  See here for an example:

http://article.gmane.org/gmane.comp.handhelds.openembedded.core/53772

Thanks,
Paul.
--

> 
> Randomize the load address of modules in the kernel to make kASLR
> effective for modules.  Modules can only be loaded within a particular
> range of virtual address space.  This patch adds 10 bits of entropy to
> the load address by adding 1-1024 * PAGE_SIZE to the beginning range
> where modules are loaded.
> 
> The single base offset was chosen because randomizing each module
> load ends up wasting/fragmenting memory too much. Prior approaches to
> minimizing fragmentation while doing randomization tend to result in
> worse entropy than just doing a single base address offset.
> 
> Example kASLR boot without this change, with a single module loaded:
> ---[ Modules ]---
> 0xffffffffc0000000-0xffffffffc0001000           4K     ro     GLB x  pte
> 0xffffffffc0001000-0xffffffffc0002000           4K     ro     GLB NX pte
> 0xffffffffc0002000-0xffffffffc0004000           8K     RW     GLB NX pte
> 0xffffffffc0004000-0xffffffffc0200000        2032K                   pte
> 0xffffffffc0200000-0xffffffffff000000        1006M                   pmd
> ---[ End Modules ]---
> 
> Example kASLR boot after this change, same module loaded:
> ---[ Modules ]---
> 0xffffffffc0000000-0xffffffffc0200000           2M                   pmd
> 0xffffffffc0200000-0xffffffffc03bf000        1788K                   pte
> 0xffffffffc03bf000-0xffffffffc03c0000           4K     ro     GLB x  pte
> 0xffffffffc03c0000-0xffffffffc03c1000           4K     ro     GLB NX pte
> 0xffffffffc03c1000-0xffffffffc03c3000           8K     RW     GLB NX pte
> 0xffffffffc03c3000-0xffffffffc0400000         244K                   pte
> 0xffffffffc0400000-0xffffffffff000000        1004M                   pmd
> ---[ End Modules ]---
> 
> Signed-off-by: Andy Honig <ahonig at google.com>
> Link: http://lkml.kernel.org/r/20140226005916.GA27083@www.outflux.net
> Signed-off-by: Kees Cook <keescook at chromium.org>
> Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
> Signed-off-by: Yang Shi <yang.shi at windriver.com>
> ---
>  Documentation/kernel-parameters.txt |  4 ++--
>  arch/x86/kernel/module.c            | 43 ++++++++++++++++++++++++++++++++++---
>  2 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 7116fda..580a60c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2053,8 +2053,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			IOAPICs that may be present in the system.
>  
>  	nokaslr		[X86]
> -			Disable kernel base offset ASLR (Address Space
> -			Layout Randomization) if built into the kernel.
> +			Disable kernel and module base offset ASLR (Address
> +			Space Layout Randomization) if built into the kernel.
>  
>  	noautogroup	Disable scheduler automatic task group creation.
>  
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index 18be189..4948313 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -28,6 +28,7 @@
>  #include <linux/mm.h>
>  #include <linux/gfp.h>
>  #include <linux/jump_label.h>
> +#include <linux/random.h>
>  
>  #include <asm/page.h>
>  #include <asm/pgtable.h>
> @@ -43,13 +44,49 @@ do {							\
>  } while (0)
>  #endif
>  
> +#ifdef CONFIG_RANDOMIZE_BASE
> +static unsigned long module_load_offset;
> +static int randomize_modules = 1;
> +
> +static int __init parse_nokaslr(char *p)
> +{
> +	randomize_modules = 0;
> +	return 0;
> +}
> +early_param("nokaslr", parse_nokaslr);
> +
> +static unsigned long int get_module_load_offset(void)
> +{
> +	if (randomize_modules) {
> +		mutex_lock(&module_mutex);
> +		/*
> +		 * Calculate the module_load_offset the first time this
> +		 * code is called. Once calculated it stays the same until
> +		 * reboot.
> +		 */
> +		if (module_load_offset == 0)
> +			module_load_offset =
> +				(get_random_int() % 1024 + 1) * PAGE_SIZE;
> +		mutex_unlock(&module_mutex);
> +	}
> +	return module_load_offset;
> +}
> +#else
> +static unsigned long int get_module_load_offset(void)
> +{
> +	return 0;
> +}
> +#endif
> +
>  void *module_alloc(unsigned long size)
>  {
>  	if (PAGE_ALIGN(size) > MODULES_LEN)
>  		return NULL;
> -	return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
> -				GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC,
> -				NUMA_NO_NODE, __builtin_return_address(0));
> +	return __vmalloc_node_range(size, 1,
> +				    MODULES_VADDR + get_module_load_offset(),
> +				    MODULES_END, GFP_KERNEL | __GFP_HIGHMEM,
> +				    PAGE_KERNEL_EXEC, NUMA_NO_NODE,
> +				    __builtin_return_address(0));
>  }
>  
>  #ifdef CONFIG_X86_32
>