Re: [PATCH v4 03/10] x86-64: Give vvars their own page

[Louis Rilling <Louis.Rilling@kerlabs.com>]

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On 31/05/11 10:14 -0400, Andy Lutomirski wrote:
> Move vvars out of the vsyscall page into their own page and mark it
> NX.
> 
> Without this patch, an attacker who can force a daemon to call some
> fixed address could wait until the time contains, say, 0xCD80, and
> then execute the current time.
> 
> Signed-off-by: Andy Lutomirski <luto@mit.edu>
> ---
>  arch/x86/include/asm/fixmap.h        |    1 +
>  arch/x86/include/asm/pgtable_types.h |    2 ++
>  arch/x86/include/asm/vvar.h          |   22 ++++++++++------------
>  arch/x86/kernel/vmlinux.lds.S        |   27 ++++++++++++++++-----------
>  arch/x86/kernel/vsyscall_64.c        |    5 +++++
>  5 files changed, 34 insertions(+), 23 deletions(-)
> 

[...]

> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 89aed99..3d89a00 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -161,12 +161,6 @@ SECTIONS
>  
>  #define VVIRT_OFFSET (VSYSCALL_ADDR - __vsyscall_0)
>  #define VVIRT(x) (ADDR(x) - VVIRT_OFFSET)
> -#define EMIT_VVAR(x, offset) .vsyscall_var_ ## x	\
> -	ADDR(.vsyscall_0) + offset		 	\
> -	: AT(VLOAD(.vsyscall_var_ ## x)) {     		\
> -		*(.vsyscall_var_ ## x)			\
> -	}						\
> -	x = VVIRT(.vsyscall_var_ ## x);
>  
>  	. = ALIGN(4096);
>  	__vsyscall_0 = .;
> @@ -192,17 +186,28 @@ SECTIONS
>  		*(.vsyscall_3)
>  	}
>  
> -#define __VVAR_KERNEL_LDS
> -#include <asm/vvar.h>
> -#undef __VVAR_KERNEL_LDS
> -
> -	. = __vsyscall_0 + PAGE_SIZE;
> +	. = ALIGN(__vsyscall_0 + PAGE_SIZE, PAGE_SIZE);
>  
>  #undef VSYSCALL_ADDR
>  #undef VLOAD_OFFSET
>  #undef VLOAD
>  #undef VVIRT_OFFSET
>  #undef VVIRT
> +
> +	__vvar_page = .;
> +
> +#define EMIT_VVAR(name, offset) .vvar_ ## name		\
> +	(__vvar_page + offset) :			\
> +	 AT(ADDR(.vvar_ ## name) - LOAD_OFFSET) {	\
> +		*(.vvar_ ## x)				\
                            ^
Maybe s/x/name/ ? -----------|

Thanks,

Louis

> +	} :data
> +
> +#define __VVAR_KERNEL_LDS
> +#include <asm/vvar.h>
> +#undef __VVAR_KERNEL_LDS
> +
> +       . = ALIGN(__vvar_page + PAGE_SIZE, PAGE_SIZE);
> +
>  #undef EMIT_VVAR
>  
>  #endif /* CONFIG_X86_64 */
> diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
> index 3e68218..3cf1cef 100644
> --- a/arch/x86/kernel/vsyscall_64.c
> +++ b/arch/x86/kernel/vsyscall_64.c
> @@ -284,9 +284,14 @@ void __init map_vsyscall(void)
>  {
>  	extern char __vsyscall_0;
>  	unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
> +	extern char __vvar_page;
> +	unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);
>  
>  	/* Note that VSYSCALL_MAPPED_PAGES must agree with the code below. */
>  	__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
> +	__set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
> +	BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
> +		     (unsigned long)VVAR_ADDRESS);
>  }
>  
>  static int __init vsyscall_init(void)
> -- 
> 1.7.5.1
> 
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-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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