From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by smtp.lore.kernel.org (Postfix) with SMTP id 70E2AC433EF for ; Thu, 13 Jan 2022 17:28:12 +0000 (UTC) Received: (qmail 3276 invoked by uid 550); 13 Jan 2022 17:27:40 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 3233 invoked from network); 13 Jan 2022 17:27:39 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642094847; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6JAs1cBVKVd9apEjPFkt89/bQIVFWGiLVSiodneQbkU=; b=Y2WKTAT6tW0wu7nySC3npPZqrEVOfUICkoDZRu154eKuITMH1drMoCGS0WBRi9egjb3bwH wy+dr3mtZOBFq7HpD8nTuITHwSsH/n+lDTdFfBXsdRJWmXGjdbVWjCKxbuCDZ/1KnCavLt 32/4FfOwe67LvyjwwB6a5UGPQLPowxg= X-MC-Unique: 3VuFLHQSP1u5wqMgynuaxw-1 From: Florian Weimer To: "Andy Lutomirski" Cc: linux-arch@vger.kernel.org, "Linux API" , linux-x86_64@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, "the arch/x86 maintainers" , musl@lists.openwall.com, , , "Dave Hansen" , "Kees Cook" , Andrei Vagin Subject: Re: [PATCH v3 1/3] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall References: <3a1c8280967b491bf6917a18fbff6c9b52e8df24.1641398395.git.fweimer@redhat.com> Date: Thu, 13 Jan 2022 18:27:15 +0100 In-Reply-To: <3a1c8280967b491bf6917a18fbff6c9b52e8df24.1641398395.git.fweimer@redhat.com> (Florian Weimer's message of "Wed, 05 Jan 2022 17:02:48 +0100") Message-ID: <874k67zguk.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 * 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 > Acked-by: Andrei Vagin > --- > 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