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 X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0923DC433DF for ; Wed, 24 Jun 2020 17:53:53 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B51DE207DD for ; Wed, 24 Jun 2020 17:53:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B51DE207DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 17AE36B0081; Wed, 24 Jun 2020 13:53:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 105896B0082; Wed, 24 Jun 2020 13:53:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E24C76B0083; Wed, 24 Jun 2020 13:53:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0214.hostedemail.com [216.40.44.214]) by kanga.kvack.org (Postfix) with ESMTP id BDA546B0081 for ; Wed, 24 Jun 2020 13:53:48 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 884E6349B for ; Wed, 24 Jun 2020 17:53:48 +0000 (UTC) X-FDA: 76964853336.06.frog82_0b0126e26e46 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id 5699110038276 for ; Wed, 24 Jun 2020 17:53:48 +0000 (UTC) X-HE-Tag: frog82_0b0126e26e46 X-Filterd-Recvd-Size: 17000 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 17:53:47 +0000 (UTC) Received: from localhost.localdomain (unknown [2.26.170.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 17C7D20899; Wed, 24 Jun 2020 17:53:44 +0000 (UTC) From: Catalin Marinas To: linux-arm-kernel@lists.infradead.org Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Andrew Morton Subject: [PATCH v5 25/25] arm64: mte: Add Memory Tagging Extension documentation Date: Wed, 24 Jun 2020 18:52:44 +0100 Message-Id: <20200624175244.25837-26-catalin.marinas@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200624175244.25837-1-catalin.marinas@arm.com> References: <20200624175244.25837-1-catalin.marinas@arm.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 5699110038276 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 Content-Transfer-Encoding: quoted-printable 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: From: Vincenzo Frascino Memory Tagging Extension (part of the ARMv8.5 Extensions) provides a mechanism to detect the sources of memory related errors which may be vulnerable to exploitation, including bounds violations, use-after-free, use-after-return, use-out-of-scope and use before initialization errors. Add Memory Tagging Extension documentation for the arm64 linux kernel support. Signed-off-by: Vincenzo Frascino Co-developed-by: Catalin Marinas Signed-off-by: Catalin Marinas Cc: Will Deacon --- Notes: v4: - Document behaviour of madvise(MADV_DONTNEED/MADV_FREE). - Document the initial process state on fork/execve. - Clarify when the kernel uaccess checks the tags. - Minor updates to the example code. - A few other minor clean-ups following review. =20 v3: - Modify the uaccess checking conditions: only when the sync mode is selected by the user. In async mode, the kernel uaccesses are not checked. - Clarify that an include mask of 0 (exclude mask 0xffff) results in always generating tag 0. - Document the ptrace() interface. =20 v2: - Documented the uaccess kernel tag checking mode. - Removed the BTI definitions from cpu-feature-registers.rst. - Removed the paragraph stating that MTE depends on the tagged addres= s ABI (while the Kconfig entry does, there is no requirement for the user to enable both). - Changed the GCR_EL1.Exclude handling description following the chan= ge in the prctl() interface (include vs exclude mask). - Updated the example code. Documentation/arm64/cpu-feature-registers.rst | 2 + Documentation/arm64/elf_hwcaps.rst | 4 + Documentation/arm64/index.rst | 1 + .../arm64/memory-tagging-extension.rst | 297 ++++++++++++++++++ 4 files changed, 304 insertions(+) create mode 100644 Documentation/arm64/memory-tagging-extension.rst diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentatio= n/arm64/cpu-feature-registers.rst index 314fa5bc2655..27d8559d565b 100644 --- a/Documentation/arm64/cpu-feature-registers.rst +++ b/Documentation/arm64/cpu-feature-registers.rst @@ -174,6 +174,8 @@ infrastructure: +------------------------------+---------+---------+ | Name | bits | visible | +------------------------------+---------+---------+ + | MTE | [11-8] | y | + +------------------------------+---------+---------+ | SSBS | [7-4] | y | +------------------------------+---------+---------+ | BT | [3-0] | y | diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf= _hwcaps.rst index 84a9fd2d41b4..bbd9cf54db6c 100644 --- a/Documentation/arm64/elf_hwcaps.rst +++ b/Documentation/arm64/elf_hwcaps.rst @@ -240,6 +240,10 @@ HWCAP2_BTI =20 Functionality implied by ID_AA64PFR0_EL1.BT =3D=3D 0b0001. =20 +HWCAP2_MTE + + Functionality implied by ID_AA64PFR1_EL1.MTE =3D=3D 0b0010, as descr= ibed + by Documentation/arm64/memory-tagging-extension.rst. =20 4. Unused AT_HWCAP bits ----------------------- diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rs= t index 09cbb4ed2237..4cd0e696f064 100644 --- a/Documentation/arm64/index.rst +++ b/Documentation/arm64/index.rst @@ -14,6 +14,7 @@ ARM64 Architecture hugetlbpage legacy_instructions memory + memory-tagging-extension pointer-authentication silicon-errata sve diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documenta= tion/arm64/memory-tagging-extension.rst new file mode 100644 index 000000000000..e7cdcecb656a --- /dev/null +++ b/Documentation/arm64/memory-tagging-extension.rst @@ -0,0 +1,297 @@ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Memory Tagging Extension (MTE) in AArch64 Linux +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Authors: Vincenzo Frascino + Catalin Marinas + +Date: 2020-02-25 + +This document describes the provision of the Memory Tagging Extension +functionality in AArch64 Linux. + +Introduction +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +ARMv8.5 based processors introduce the Memory Tagging Extension (MTE) +feature. MTE is built on top of the ARMv8.0 virtual address tagging TBI +(Top Byte Ignore) feature and allows software to access a 4-bit +allocation tag for each 16-byte granule in the physical address space. +Such memory range must be mapped with the Normal-Tagged memory +attribute. A logical tag is derived from bits 59-56 of the virtual +address used for the memory access. A CPU with MTE enabled will compare +the logical tag against the allocation tag and potentially raise an +exception on mismatch, subject to system registers configuration. + +Userspace Support +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +When ``CONFIG_ARM64_MTE`` is selected and Memory Tagging Extension is +supported by the hardware, the kernel advertises the feature to +userspace via ``HWCAP2_MTE``. + +PROT_MTE +-------- + +To access the allocation tags, a user process must enable the Tagged +memory attribute on an address range using a new ``prot`` flag for +``mmap()`` and ``mprotect()``: + +``PROT_MTE`` - Pages allow access to the MTE allocation tags. + +The allocation tag is set to 0 when such pages are first mapped in the +user address space and preserved on copy-on-write. ``MAP_SHARED`` is +supported and the allocation tags can be shared between processes. + +**Note**: ``PROT_MTE`` is only supported on ``MAP_ANONYMOUS`` and +RAM-based file mappings (``tmpfs``, ``memfd``). Passing it to other +types of mapping will result in ``-EINVAL`` returned by these system +calls. + +**Note**: The ``PROT_MTE`` flag (and corresponding memory type) cannot +be cleared by ``mprotect()``. + +**Note**: ``madvise()`` memory ranges with ``MADV_DONTNEED`` and +``MADV_FREE`` may have the allocation tags cleared (set to 0) at any +point after the system call. + +Tag Check Faults +---------------- + +When ``PROT_MTE`` is enabled on an address range and a mismatch between +the logical and allocation tags occurs on access, there are three +configurable behaviours: + +- *Ignore* - This is the default mode. The CPU (and kernel) ignores the + tag check fault. + +- *Synchronous* - The kernel raises a ``SIGSEGV`` synchronously, with + ``.si_code =3D SEGV_MTESERR`` and ``.si_addr =3D ``. Th= e + memory access is not performed. If ``SIGSEGV`` is ignored or blocked + by the offending thread, the containing process is terminated with a + ``coredump``. + +- *Asynchronous* - The kernel raises a ``SIGSEGV``, in the offending + thread, asynchronously following one or multiple tag check faults, + with ``.si_code =3D SEGV_MTEAERR`` and ``.si_addr =3D 0`` (the faultin= g + address is unknown). + +The user can select the above modes, per thread, using the +``prctl(PR_SET_TAGGED_ADDR_CTRL, flags, 0, 0, 0)`` system call where +``flags`` contain one of the following values in the ``PR_MTE_TCF_MASK`` +bit-field: + +- ``PR_MTE_TCF_NONE`` - *Ignore* tag check faults +- ``PR_MTE_TCF_SYNC`` - *Synchronous* tag check fault mode +- ``PR_MTE_TCF_ASYNC`` - *Asynchronous* tag check fault mode + +The current tag check fault mode can be read using the +``prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0)`` system call. + +Tag checking can also be disabled for a user thread by setting the +``PSTATE.TCO`` bit with ``MSR TCO, #1``. + +**Note**: Signal handlers are always invoked with ``PSTATE.TCO =3D 0``, +irrespective of the interrupted context. ``PSTATE.TCO`` is restored on +``sigreturn()``. + +**Note**: There are no *match-all* logical tags available for user +applications. + +**Note**: Kernel accesses to the user address space (e.g. ``read()`` +system call) are not checked if the user thread tag checking mode is +``PR_MTE_TCF_NONE`` or ``PR_MTE_TCF_ASYNC``. If the tag checking mode is +``PR_MTE_TCF_SYNC``, the kernel makes a best effort to check its user +address accesses, however it cannot always guarantee it. + +Excluding Tags in the ``IRG``, ``ADDG`` and ``SUBG`` instructions +----------------------------------------------------------------- + +The architecture allows excluding certain tags to be randomly generated +via the ``GCR_EL1.Exclude`` register bit-field. By default, Linux +excludes all tags other than 0. A user thread can enable specific tags +in the randomly generated set using the ``prctl(PR_SET_TAGGED_ADDR_CTRL, +flags, 0, 0, 0)`` system call where ``flags`` contains the tags bitmap +in the ``PR_MTE_TAG_MASK`` bit-field. + +**Note**: The hardware uses an exclude mask but the ``prctl()`` +interface provides an include mask. An include mask of ``0`` (exclusion +mask ``0xffff``) results in the CPU always generating tag ``0``. + +Initial process state +--------------------- + +On ``execve()``, the new process has the following configuration: + +- ``PR_TAGGED_ADDR_ENABLE`` set to 0 (disabled) +- Tag checking mode set to ``PR_MTE_TCF_NONE`` +- ``PR_MTE_TAG_MASK`` set to 0 (all tags excluded) +- ``PSTATE.TCO`` set to 0 +- ``PROT_MTE`` not set on any of the initial memory maps + +On ``fork()``, the new process inherits the parent's configuration and +memory map attributes with the exception of the ``madvise()`` ranges +with ``MADV_WIPEONFORK`` which will have the data and tags cleared (set +to 0). + +The ``ptrace()`` interface +-------------------------- + +``PTRACE_PEEKMTETAGS`` and ``PTRACE_POKEMTETAGS`` allow a tracer to read +the tags from or set the tags to a tracee's address space. The +``ptrace()`` system call is invoked as ``ptrace(request, pid, addr, +data)`` where: + +- ``request`` - one of ``PTRACE_PEEKMTETAGS`` or ``PTRACE_PEEKMTETAGS``. +- ``pid`` - the tracee's PID. +- ``addr`` - address in the tracee's address space. +- ``data`` - pointer to a ``struct iovec`` where ``iov_base`` points to + a buffer of ``iov_len`` length in the tracer's address space. + +The tags in the tracer's ``iov_base`` buffer are represented as one +4-bit tag per byte and correspond to a 16-byte MTE tag granule in the +tracee's address space. + +**Note**: If ``addr`` is not aligned to a 16-byte granule, the kernel +will use the corresponding aligned address. + +``ptrace()`` return value: + +- 0 - tags were copied, the tracer's ``iov_len`` was updated to the + number of tags transferred. This may be smaller than the requested + ``iov_len`` if the requested address range in the tracee's or the + tracer's space cannot be accessed or does not have valid tags. +- ``-EPERM`` - the specified process cannot be traced. +- ``-EIO`` - the tracee's address range cannot be accessed (e.g. invalid + address) and no tags copied. ``iov_len`` not updated. +- ``-EFAULT`` - fault on accessing the tracer's memory (``struct iovec`` + or ``iov_base`` buffer) and no tags copied. ``iov_len`` not updated. +- ``-EOPNOTSUPP`` - the tracee's address does not have valid tags (never + mapped with the ``PROT_MTE`` flag). ``iov_len`` not updated. + +**Note**: There are no transient errors for the requests above, so user +programs should not retry in case of a non-zero system call return. + +Example of correct usage +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +*MTE Example code* + +.. code-block:: c + + /* + * To be compiled with -march=3Darmv8.5-a+memtag + */ + #include + #include + #include + #include + #include + #include + #include + + /* + * From arch/arm64/include/uapi/asm/hwcap.h + */ + #define HWCAP2_MTE (1 << 18) + + /* + * From arch/arm64/include/uapi/asm/mman.h + */ + #define PROT_MTE 0x20 + + /* + * From include/uapi/linux/prctl.h + */ + #define PR_SET_TAGGED_ADDR_CTRL 55 + #define PR_GET_TAGGED_ADDR_CTRL 56 + # define PR_TAGGED_ADDR_ENABLE (1UL << 0) + # define PR_MTE_TCF_SHIFT 1 + # define PR_MTE_TCF_NONE (0UL << PR_MTE_TCF_SHIFT) + # define PR_MTE_TCF_SYNC (1UL << PR_MTE_TCF_SHIFT) + # define PR_MTE_TCF_ASYNC (2UL << PR_MTE_TCF_SHIFT) + # define PR_MTE_TCF_MASK (3UL << PR_MTE_TCF_SHIFT) + # define PR_MTE_TAG_SHIFT 3 + # define PR_MTE_TAG_MASK (0xffffUL << PR_MTE_TAG_SHIFT) + + /* + * Insert a random logical tag into the given pointer. + */ + #define insert_random_tag(ptr) ({ \ + __u64 __val; \ + asm("irg %0, %1" : "=3Dr" (__val) : "r" (ptr)); \ + __val; \ + }) + + /* + * Set the allocation tag on the destination address. + */ + #define set_tag(tagged_addr) do { = \ + asm volatile("stg %0, [%0]" : : "r" (tagged_addr) : "memory"= ); \ + } while (0) + + int main() + { + unsigned char *a; + unsigned long page_sz =3D sysconf(_SC_PAGESIZE); + unsigned long hwcap2 =3D getauxval(AT_HWCAP2); + + /* check if MTE is present */ + if (!(hwcap2 & HWCAP2_MTE)) + return EXIT_FAILURE; + + /* + * Enable the tagged address ABI, synchronous MTE tag check = faults and + * allow all non-zero tags in the randomly generated set. + */ + if (prctl(PR_SET_TAGGED_ADDR_CTRL, + PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | (0xfffe = << PR_MTE_TAG_SHIFT), + 0, 0, 0)) { + perror("prctl() failed"); + return EXIT_FAILURE; + } + + a =3D mmap(0, page_sz, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (a =3D=3D MAP_FAILED) { + perror("mmap() failed"); + return EXIT_FAILURE; + } + + /* + * Enable MTE on the above anonymous mmap. The flag could be= passed + * directly to mmap() and skip this step. + */ + if (mprotect(a, page_sz, PROT_READ | PROT_WRITE | PROT_MTE))= { + perror("mprotect() failed"); + return EXIT_FAILURE; + } + + /* access with the default tag (0) */ + a[0] =3D 1; + a[1] =3D 2; + + printf("a[0] =3D %hhu a[1] =3D %hhu\n", a[0], a[1]); + + /* set the logical and allocation tags */ + a =3D (unsigned char *)insert_random_tag(a); + set_tag(a); + + printf("%p\n", a); + + /* non-zero tag access */ + a[0] =3D 3; + printf("a[0] =3D %hhu a[1] =3D %hhu\n", a[0], a[1]); + + /* + * If MTE is enabled correctly the next instruction will gen= erate an + * exception. + */ + printf("Expecting SIGSEGV...\n"); + a[16] =3D 0xdd; + + /* this should not be printed in the PR_MTE_TCF_SYNC mode */ + printf("...haven't got one\n"); + + return EXIT_FAILURE; + }