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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1F21C47074 for ; Thu, 4 Jan 2024 23:47:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 46D9E6B02F9; Thu, 4 Jan 2024 18:47:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F61D6B02FA; Thu, 4 Jan 2024 18:47:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 296F06B02FB; Thu, 4 Jan 2024 18:47:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 0B4646B02F9 for ; Thu, 4 Jan 2024 18:47:49 -0500 (EST) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id CF9B7A05F8 for ; Thu, 4 Jan 2024 23:47:48 +0000 (UTC) X-FDA: 81643268616.26.D9E7989 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf24.hostedemail.com (Postfix) with ESMTP id AB25D180010 for ; Thu, 4 Jan 2024 23:47:45 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=hYVjkgeA; dmarc=none; spf=none (imf24.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1704412066; h=from:from:sender: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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=9tIXMgL1ffvscpIB5M1yXbHsKCQtrFxaC60vt7+1wLM=; b=iTBW9oLgwV9WCM19m+GdgsymgpcHhhduTCf/vzvima/6vItkNTMAe4DYndqrsmI9R2coXt 4OFxIMX3Uu6/fRCSbYDBkcNcHQfIEihdJmdS8tzjAV+z53RdULTt1EBO4ItjU+2BfP3yu/ Yv3qwcpk03xA1TdTG8qktARrAV78DWw= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=hYVjkgeA; dmarc=none; spf=none (imf24.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1704412066; a=rsa-sha256; cv=none; b=BUvobA+l5JTFtw+W8xqZe9MKLBEpLb1TANUCaZl78dyXlUfE/sIunE4+TPuuX9ZzBVHQG3 DjQffCVGQHqbVdnjqB4rWUJHNadXiuQpYCJZNlb0AQilNc9gHcZX8O0tbd+QJENWH3qAIq O+xm8sf3SlehflR8wq+hri38/FbvC2E= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Sender:Reply-To:Content-ID:Content-Description; bh=9tIXMgL1ffvscpIB5M1yXbHsKCQtrFxaC60vt7+1wLM=; b=hYVjkgeAkvxZ/X5SSiOGUweDdT XwJTgoHCg8p20AwnDjlddkd7XnWUrgp5KB4gFQXhOpFDRJzaHnvL2wzk4UwUDf6cEREWmYJv+N6nl jaKuJ8pv0HpEjxIKbBpd1yjluelpaMJ35Qv2E9RU1yInlrfamxlLwYtie+IFbkVnoEUdegopbI3du LV4st/3ZwsV+BrLDD7VFLEb4xWElK6QqK1LxbLlAeaxQ5Z2uTIrqbDeMU/KGtp9T9OFP4PXjxhSJR 7frRSptan4h9mp1FhWqe3VH42PlSM1ji6qhD7jpAEKi1hxlRSPOINxbd+STryzftyx8qz/xsI7COx iBttwnbQ==; Received: from [50.53.46.231] (helo=[192.168.254.15]) by bombadil.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1rLXR3-00Fb5K-0q; Thu, 04 Jan 2024 23:47:37 +0000 Message-ID: <796b6877-0548-4d2a-a484-ba4156104a20@infradead.org> Date: Thu, 4 Jan 2024 15:47:36 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 4/4] mseal:add documentation Content-Language: en-US To: jeffxu@chromium.org, akpm@linux-foundation.org, keescook@chromium.org, jannh@google.com, sroettger@google.com, willy@infradead.org, gregkh@linuxfoundation.org, torvalds@linux-foundation.org, usama.anjum@collabora.com Cc: jeffxu@google.com, jorgelo@chromium.org, groeck@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, pedro.falcato@gmail.com, dave.hansen@intel.com, linux-hardening@vger.kernel.org, deraadt@openbsd.org References: <20240104185138.169307-1-jeffxu@chromium.org> <20240104185138.169307-5-jeffxu@chromium.org> From: Randy Dunlap In-Reply-To: <20240104185138.169307-5-jeffxu@chromium.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AB25D180010 X-Stat-Signature: fac3c54jyhy8pc37phokhskfja19gi16 X-HE-Tag: 1704412065-492085 X-HE-Meta: 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 0f5xpGgc 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 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: List-Subscribe: List-Unsubscribe: On 1/4/24 10:51, jeffxu@chromium.org wrote: > From: Jeff Xu > > Add documentation for mseal(). > > Signed-off-by: Jeff Xu > --- > Documentation/userspace-api/mseal.rst | 181 ++++++++++++++++++++++++++ > 1 file changed, 181 insertions(+) > create mode 100644 Documentation/userspace-api/mseal.rst > > diff --git a/Documentation/userspace-api/mseal.rst b/Documentation/userspace-api/mseal.rst > new file mode 100644 > index 000000000000..1700ce5af218 > --- /dev/null > +++ b/Documentation/userspace-api/mseal.rst > @@ -0,0 +1,181 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +===================== > +Introduction of mseal > +===================== > + > +:Author: Jeff Xu > + > +Modern CPUs support memory permissions such as RW and NX bits. The memory > +permission feature improves security stance on memory corruption bugs, i.e. > +the attacker can’t just write to arbitrary memory and point the code to it, > +the memory has to be marked with X bit, or else an exception will happen. > + > +Memory sealing additionally protects the mapping itself against > +modifications. This is useful to mitigate memory corruption issues where a > +corrupted pointer is passed to a memory management system. For example, > +such an attacker primitive can break control-flow integrity guarantees > +since read-only memory that is supposed to be trusted can become writable > +or .text pages can get remapped. Memory sealing can automatically be > +applied by the runtime loader to seal .text and .rodata pages and > +applications can additionally seal security critical data at runtime. > + > +A similar feature already exists in the XNU kernel with the > +VM_FLAGS_PERMANENT flag [1] and on OpenBSD with the mimmutable syscall [2]. > + > +User API > +======== > +Two system calls are involved in virtual memory sealing, mseal() and mmap(). > + > +mseal() > +----------- > +The mseal() syscall has following signature: > + > +``int mseal(void addr, size_t len, unsigned long flags)`` > + > +**addr/len**: virtual memory address range. > + > +The address range set by ``addr``/``len`` must meet: > + - The start address must be in an allocated VMA. > + - The start address must be page aligned. > + - The end address (``addr`` + ``len``) must be in an allocated VMA. > + - no gap (unallocated memory) between start and end address. > + > +The ``len`` will be paged aligned implicitly by the kernel. Does that mean that the will be extended to be page aligned if it's not already page aligned? > + > +**flags**: reserved for future use. > + > +**return values**: > + > +- ``0``: Success. > + > +- ``-EINVAL``: > + - Invalid input ``flags``. > + - The start address (``addr``) is not page aligned. > + - Address range (``addr`` + ``len``) overflow. > + > +- ``-ENOMEM``: > + - The start address (``addr``) is not allocated. > + - The end address (``addr`` + ``len``) is not allocated. > + - A gap (unallocated memory) between start and end address. > + > +- ``-EACCES``: > + - ``MAP_SEALABLE`` is not set during mmap(). > + > +- ``-EPERM``: > + - sealing is supported only on 64 bit CPUs, 32-bit is not supported. 64-bit > + > +- For above error cases, users can expect the given memory range is > + unmodified, i.e. no partial update. > + > +- There might be other internal errors/cases not listed here, e.g. > + error during merging/splitting VMAs, or the process reaching the max > + number of supported VMAs. In those cases, partial updates to the given > + memory range could happen. However, those cases shall be rare. > + > +**Blocked operations after sealing**: > + Unmapping, moving to another location, and shrinking the size, > + via munmap() and mremap(), can leave an empty space, therefore > + can be replaced with a VMA with a new set of attributes. > + > + Moving or expanding a different VMA into the current location, > + via mremap(). > + > + Modifying a VMA via mmap(MAP_FIXED). > + > + Size expansion, via mremap(), does not appear to pose any > + specific risks to sealed VMAs. It is included anyway because > + the use case is unclear. In any case, users can rely on > + merging to expand a sealed VMA. > + > + mprotect() and pkey_mprotect(). > + > + Some destructive madvice() behaviors (e.g. MADV_DONTNEED) > + for anonymous memory, when users don't have write permission to the > + memory. Those behaviors can alter region contents by discarding pages, > + effectively a memset(0) for anonymous memory. > + > +**Note**: > + > +- mseal() only works on 64-bit CPUs, not 32-bit CPU. > + > +- users can call mseal() multiple times, mseal() on an already sealed memory times; > + is a no-action (not error). > + > +- munseal() is not supported. > + > +mmap() > +---------- > +``void *mmap(void* addr, size_t length, int prot, int flags, int fd, > +off_t offset);`` > + > +We add two changes in ``prot`` and ``flags`` of mmap() related to > +memory sealing. > + > +**prot** > + > +The ``PROT_SEAL`` bit in ``prot`` field of mmap(). > + > +When present, it marks the memory is sealed since creation. > + > +This is useful as optimization because it avoids having to make two > +system calls: one for mmap() and one for mseal(). > + > +It's worth noting that even though the sealing is set via the > +``prot`` field in mmap(), it can't be set in the ``prot`` > +field in later mprotect(). This is unlike the ``PROT_READ``, > +``PROT_WRITE``, ``PROT_EXEC`` bits, e.g. if ``PROT_WRITE`` is not set in > +mprotect(), it means that the region is not writable. > + > +Setting ``PROT_SEAL`` implies setting ``MAP_SEALABLE`` below. > + > +**flags** > + > +The ``MAP_SEALABLE`` bit in the ``flags`` field of mmap(). > + > +When present, it marks the map as sealable. A map created > +without ``MAP_SEALABLE`` will not support sealing; In other words, > +mseal() will fail for such a map. > + > + > +Applications that don't care about sealing will expect their > +behavior unchanged. For those that need sealing support, opt-in > +by adding ``MAP_SEALABLE`` in mmap(). > + > +Note: for a map created without ``MAP_SEALABLE`` or a map created > +with ``MAP_SEALABLE`` but not sealed yet, mmap(MAP_FIXED) can > +change the sealable or sealing bit. > + > +Use Case: > +========= > +- glibc: > + The dynamic linker, during loading ELF executables, can apply sealing to during loading of or while loading > + non-writable memory segments. > + > +- Chrome browser: protect some security sensitive data-structures. security-sensitive data structures. > + > +Additional notes: > +================= > +As Jann Horn pointed out in [3], there are still a few ways to write > +to RO memory, which is, in a way, by design. Those cases are not covered > +by mseal(). If applications want to block such cases, sandbox tools (such as > +seccomp, LSM, etc) might be considered. > + > +Those cases are: > + > +- Write to read-only memory through /proc/self/mem interface. > +- Write to read-only memory through ptrace (such as PTRACE_POKETEXT). > +- userfaultfd. > + > +The idea that inspired this patch comes from Stephen Röttger’s work in V8 > +CFI [4]. Chrome browser in ChromeOS will be the first user of this API. > + > +Reference: > +========== > +[1] https://github.com/apple-oss-distributions/xnu/blob/1031c584a5e37aff177559b9f69dbd3c8c3fd30a/osfmk/mach/vm_statistics.h#L274 > + > +[2] https://man.openbsd.org/mimmutable.2 > + > +[3] https://lore.kernel.org/lkml/CAG48ez3ShUYey+ZAFsU2i1RpQn0a5eOs2hzQ426FkcgnfUGLvA@mail.gmail.com > + > +[4] https://docs.google.com/document/d/1O2jwK4dxI3nRcOJuPYkonhTkNQfbmwdvxQMyXgeaRHo/edit#heading=h.bvaojj9fu6hc -- #Randy