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[2a01:4f8:190:11c2::b:1457]) by mx.google.com with ESMTPS id x1si7579989wru.294.2019.02.11.10.29.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Feb 2019 10:29:59 -0800 (PST) Received-SPF: pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) client-ip=2a01:4f8:190:11c2::b:1457; Authentication-Results: mx.google.com; dkim=pass header.i=@alien8.de header.s=dkim header.b=dj10XbPz; spf=pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) smtp.mailfrom=bp@alien8.de; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alien8.de Received: from zn.tnic (p200300EC2BC7A10074DEFDFE3AD6CF32.dip0.t-ipconnect.de [IPv6:2003:ec:2bc7:a100:74de:fdfe:3ad6:cf32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 1C0D71EC037B; Mon, 11 Feb 2019 19:29:58 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1549909798; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=Yw+RK9f/S+johjl1gYKTeZptuEY0P9nfhJd0XlVQGCo=; b=dj10XbPzFbFnu9Nya4W5OkkNbXxJnnkj4Hr1SOpZ2asDUWMbDzAbKRWRj/tjz/qk4tl7WJ 0em21jvddg2A3nLTY/GpXAXUxfmJCaIUKjSFW1JC6HHKlJLE1/k9VIlZrqJLUkJ0JPA/M4 LmZjPdIjqu1x0Cyl6ehJazATSPz8JTc= Date: Mon, 11 Feb 2019 19:29:56 +0100 From: Borislav Petkov To: Rick Edgecombe Cc: Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, Thomas Gleixner , Nadav Amit , Dave Hansen , Peter Zijlstra , linux_dti@icloud.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, akpm@linux-foundation.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, will.deacon@arm.com, ard.biesheuvel@linaro.org, kristen@linux.intel.com, deneen.t.dock@intel.com, Nadav Amit , Kees Cook , Dave Hansen , Masami Hiramatsu Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading Message-ID: <20190211182956.GN19618@zn.tnic> References: <20190129003422.9328-1-rick.p.edgecombe@intel.com> <20190129003422.9328-11-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190129003422.9328-11-rick.p.edgecombe@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading For your next submission, please fix all your subjects: The tip tree preferred format for patch subject prefixes is 'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:', 'genirq/core:'. Please do not use file names or complete file paths as prefix. 'git log path/to/file' should give you a reasonable hint in most cases. The condensed patch description in the subject line should start with a uppercase letter and should be written in imperative tone. On Mon, Jan 28, 2019 at 04:34:12PM -0800, Rick Edgecombe wrote: > From: Nadav Amit > > When modules and BPF filters are loaded, there is a time window in > which some memory is both writable and executable. An attacker that has > already found another vulnerability (e.g., a dangling pointer) might be > able to exploit this behavior to overwrite kernel code. > > Prevent having writable executable PTEs in this stage. In addition, > avoiding having W+X mappings can also slightly simplify the patching of > modules code on initialization (e.g., by alternatives and static-key), > as would be done in the next patch. > > To avoid having W+X mappings, set them initially as RW (NX) and after > they are set as RO set them as X as well. Setting them as executable is > done as a separate step to avoid one core in which the old PTE is cached > (hence writable), and another which sees the updated PTE (executable), > which would break the W^X protection. > > Cc: Kees Cook > Cc: Peter Zijlstra > Cc: Dave Hansen > Cc: Masami Hiramatsu > Suggested-by: Thomas Gleixner > Suggested-by: Andy Lutomirski > Signed-off-by: Nadav Amit > Signed-off-by: Rick Edgecombe > --- > arch/x86/kernel/alternative.c | 28 +++++++++++++++++++++------- > arch/x86/kernel/module.c | 2 +- > include/linux/filter.h | 2 +- > kernel/module.c | 5 +++++ > 4 files changed, 28 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 76d482a2b716..69f3e650ada8 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -667,15 +667,29 @@ void __init alternative_instructions(void) > * handlers seeing an inconsistent instruction while you patch. > */ > void *__init_or_module text_poke_early(void *addr, const void *opcode, > - size_t len) > + size_t len) > { > unsigned long flags; > - local_irq_save(flags); > - memcpy(addr, opcode, len); > - local_irq_restore(flags); > - sync_core(); > - /* Could also do a CLFLUSH here to speed up CPU recovery; but > - that causes hangs on some VIA CPUs. */ > + > + if (static_cpu_has(X86_FEATURE_NX) && Not a fast path - boot_cpu_has() is fine here. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.