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Message-ID: <20180307193110.GA3307@isilmar-4.linta.de> Date: Wed, 7 Mar 2018 20:31:10 +0100 From: Dominik Brodowski <linux@...inikbrodowski.net> To: Kees Cook <keescook@...omium.org> Cc: Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Borislav Petkov <bp@...en8.de> Subject: Re: [PATCH] x86/vsyscall/64: Drop "native" vsyscalls On Wed, Mar 07, 2018 at 11:21:46AM -0800, Kees Cook wrote: > On Wed, Mar 7, 2018 at 11:12 AM, Andy Lutomirski <luto@...nel.org> wrote: > > Since Linux 3.2, vsyscalls have been deprecated and slow. From 3.2 > > on, Linux had three vsyscall modes: "native", "emulate", and "none". > > > > "emulate" is the default. All known user programs work correctly in > > emulate mode, but vsyscalls turn into page faults and are emulated. > > This is very slow. In "native" mode, the vsyscall page is easily > > usable as an exploit gadget, but vsyscalls are a bit faster -- they > > turn into normal syscalls. (This is in contrast to vDSO functions, > > which can be much faster than syscalls.) In "none" mode, there are > > no vsyscalls. > > > > For all practical purposes, "native" was really just a chicken bit > > in case something went wrong with the emulation. It's been over six > > years, and nothing has gone wrong. Delete it. > > > > Signed-off-by: Andy Lutomirski <luto@...nel.org> > > Acked-by: Kees Cook <keescook@...omium.org> > > I related news, I wonder how long before we can switch from EMULATE to > NONE as the default? glibc 2.15 (which stopped using vsyscall) is (not > coincidentally) 6 years old too... Or, in the meantime, add a warning if (vsyscall_mode == EMULATE) { warn_bad_vsyscall(KERN_INFO, regs, "vsyscalls are deprecated -- use vDSO instead"); } Otherwise, the patch looks good. Thanks, Dominik
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