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Date: Mon, 10 Jun 2019 13:44:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
Borislav Petkov <bp@...en8.de>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/5] x86/vsyscall: Change the default vsyscall mode to
xonly
On Mon, Jun 10, 2019 at 01:25:31PM -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.
Perhaps describe the esoteric cases here (and maybe in the Kconfig help
text)? That should a user determine if they actually need it. (What
would the failure under xonly look like for someone needing emulate?)
-Kees
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> arch/x86/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 054033cc4b1b..e56f33e6b045 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2280,7 +2280,7 @@ 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
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