Re: [PATCH v2 6/8] x86/vsyscall: Change the default vsyscall mode to xonly

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:07PM -0700, Andy Lutomirski wrote:
> The use case for full emulation over xonly is very esoteric.  Let's
> change the default to the safer xonly mode.
> 
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>

I still think it'd be valuable to describe any known esoteric cases
here, but regardless:

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/x86/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0182d2c67590..32028edc1b0e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2285,7 +2285,7 @@ config COMPAT_VDSO
>  choice
>  	prompt "vsyscall table for legacy applications"
>  	depends on X86_64
> -	default LEGACY_VSYSCALL_EMULATE
> +	default LEGACY_VSYSCALL_XONLY
>  	help
>  	  Legacy user code that does not know how to find the vDSO expects
>  	  to be able to issue three syscalls by calling fixed addresses in
> -- 
> 2.21.0
> 

-- 
Kees Cook