Date: Thu, 13 Jan 2022 18:27:15 +0100 From: Florian Weimer <fweimer@...hat.com> To: "Andy Lutomirski" <luto@...nel.org> Cc: linux-arch@...r.kernel.org, "Linux API" <linux-api@...r.kernel.org>, linux-x86_64@...r.kernel.org, kernel-hardening@...ts.openwall.com, linux-mm@...ck.org, "the arch/x86 maintainers" <x86@...nel.org>, musl@...ts.openwall.com, <libc-alpha@...rceware.org>, <linux-kernel@...r.kernel.org>, "Dave Hansen" <dave.hansen@...el.com>, "Kees Cook" <keescook@...omium.org>, Andrei Vagin <avagin@...il.com> Subject: Re: [PATCH v3 1/3] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall * Florian Weimer: > Distributions struggle with changing the default for vsyscall > emulation because it is a clear break of userspace ABI, something > that should not happen. > > The legacy vsyscall interface is supposed to be used by libcs only, > not by applications. This commit adds a new arch_prctl request, > ARCH_VSYSCALL_CONTROL, with one argument. If the argument is 0, > executing vsyscalls will cause the process to terminate. Argument 1 > turns vsyscall back on (this is mostly for a largely theoretical > CRIU use case). > > Newer libcs can use a zero ARCH_VSYSCALL_CONTROL at startup to disable > vsyscall for the process. Legacy libcs do not perform this call, so > vsyscall remains enabled for them. This approach should achieves > backwards compatibility (perfect compatibility if the assumption that > only libcs use vsyscall is accurate), and it provides full hardening > for new binaries. > > The chosen value of ARCH_VSYSCALL_CONTROL should avoid conflicts > with other x86-64 arch_prctl requests. The fact that with > vsyscall=emulate, reading the vsyscall region is still possible > even after a zero ARCH_VSYSCALL_CONTROL is considered limitation > in the current implementation and may change in a future kernel > version. > > Future arch_prctls requests commonly used at process startup can imply > ARCH_VSYSCALL_CONTROL with a zero argument, so that a separate system > call for disabling vsyscall is avoided. > > Signed-off-by: Florian Weimer <fweimer@...hat.com> > Acked-by: Andrei Vagin <avagin@...il.com> > --- > v3: Remove warning log message. Split out test. > v2: ARCH_VSYSCALL_CONTROL instead of ARCH_VSYSCALL_LOCKOUT. New tests > for the toggle behavior. Implement hiding [vsyscall] in > /proc/PID/maps and test it. Various other test fixes cleanups > (e.g., fixed missing second argument to gettimeofday). > > arch/x86/entry/vsyscall/vsyscall_64.c | 7 ++++++- > arch/x86/include/asm/mmu.h | 6 ++++++ > arch/x86/include/uapi/asm/prctl.h | 2 ++ > arch/x86/kernel/process_64.c | 7 +++++++ > 4 files changed, 21 insertions(+), 1 deletion(-) Hello, sorry to bother you again. What can I do to move this forward? Thanks, Florian
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