= Intro = The patchset brings enabling of Intel Multi-Key Total Memory Encryption. It consists of changes into multiple subsystems: * Core MM: infrastructure for allocation pages, dealing with encrypted VMAs and providing API setup encrypted mappings. * arch/x86: feature enumeration, program keys into hardware, setup page table entries for encrypted pages and more. * Key management service: setup and management of encryption keys. * DMA/IOMMU: dealing with encrypted memory on IO side. * KVM: interaction with virtualization side. * Documentation: description of APIs and usage examples. The patchset is huge. This submission aims to give view to the full picture and get feedback on the overall design. The patchset will be split into more digestible pieces later. Please review. Any feedback is welcome. = Overview = Multi-Key Total Memory Encryption (MKTME)[1] is a technology that allows transparent memory encryption in upcoming Intel platforms. It uses a new instruction (PCONFIG) for key setup and selects a key for individual pages by repurposing physical address bits in the page tables. These patches add support for MKTME into the existing kernel keyring subsystem and add a new mprotect_encrypt() system call that can be used by applications to encrypt anonymous memory with keys obtained from the keyring. This architecture supports encrypting both normal, volatile DRAM and persistent memory. However, these patches do not implement persistent memory support. We anticipate adding that support next. == Hardware Background == MKTME is built on top of an existing single-key technology called TME. TME encrypts all system memory using a single key generated by the CPU on every boot of the system. TME provides mitigation against physical attacks, such as physically removing a DIMM or watching memory bus traffic. MKTME enables the use of multiple encryption keys[2], allowing selection of the encryption key per-page using the page tables. Encryption keys are programmed into each memory controller and the same set of keys is available to all entities on the system with access to that memory (all cores, DMA engines, etc...). MKTME inherits many of the mitigations against hardware attacks from TME. Like TME, MKTME does not mitigate vulnerable or malicious operating systems or virtual machine managers. MKTME offers additional mitigations when compared to TME. TME and MKTME use the AES encryption algorithm in the AES-XTS mode. This mode, typically used for block-based storage devices, takes the physical address of the data into account when encrypting each block. This ensures that the effective key is different for each block of memory. Moving encrypted content across physical address results in garbage on read, mitigating block-relocation attacks. This property is the reason many of the discussed attacks require control of a shared physical page to be handed from the victim to the attacker. == MKTME-Provided Mitigations == MKTME adds a few mitigations against attacks that are not mitigated when using TME alone. The first set are mitigations against software attacks that are familiar today: * Kernel Mapping Attacks: information disclosures that leverage the kernel direct map are mitigated against disclosing user data. * Freed Data Leak Attacks: removing an encryption key from the hardware mitigates future user information disclosure. The next set are attacks that depend on specialized hardware, such as an “evil DIMM” or a DDR interposer: * Cross-Domain Replay Attack: data is captured from one domain (guest) and replayed to another at a later time. * Cross-Domain Capture and Delayed Compare Attack: data is captured and later analyzed to discover secrets. * Key Wear-out Attack: data is captured and analyzed in order to Weaken the AES encryption itself. More details on these attacks are below. === Kernel Mapping Attacks === Information disclosure vulnerabilities leverage the kernel direct map because many vulnerabilities involve manipulation of kernel data structures (examples: CVE-2017-7277, CVE-2017-9605). We normally think of these bugs as leaking valuable *kernel* data, but they can leak application data when application pages are recycled for kernel use. With this MKTME implementation, there is a direct map created for each MKTME KeyID which is used whenever the kernel needs to access plaintext. But, all kernel data structures are accessed via the direct map for KeyID-0. Thus, memory reads which are not coordinated with the KeyID get garbage (for example, accessing KeyID-4 data with the KeyID-0 mapping). This means that if sensitive data encrypted using MKTME is leaked via the KeyID-0 direct map, ciphertext decrypted with the wrong key will be disclosed. To disclose plaintext, an attacker must “pivot” to the correct direct mapping, which is non-trivial because there are no kernel data structures in the KeyID!=0 direct mapping. === Freed Data Leak Attack === The kernel has a history of bugs around uninitialized data. Usually, we think of these bugs as leaking sensitive kernel data, but they can also be used to leak application secrets. MKTME can help mitigate the case where application secrets are leaked: * App (or VM) places a secret in a page * App exits or frees memory to kernel allocator * Page added to allocator free list * Attacker reallocates page to a purpose where it can read the page Now, imagine MKTME was in use on the memory being leaked. The data can only be leaked as long as the key is programmed in the hardware. If the key is de-programmed, like after all pages are freed after a guest is shut down, any future reads will just see ciphertext. Basically, the key is a convenient choke-point: you can be more confident that data encrypted with it is inaccessible once the key is removed. === Cross-Domain Replay Attack === MKTME mitigates cross-domain replay attacks where an attacker replaces an encrypted block owned by one domain with a block owned by another domain. MKTME does not prevent this replacement from occurring, but it does mitigate plaintext from being disclosed if the domains use different keys. With TME, the attack could be executed by: * A victim places secret in memory, at a given physical address. Note: AES-XTS is what restricts the attack to being performed at a single physical address instead of across different physical addresses * Attacker captures victim secret’s ciphertext * Later on, after victim frees the physical address, attacker gains ownership * Attacker puts the ciphertext at the address and get the secret plaintext But, due to the presumably different keys used by the attacker and the victim, the attacker can not successfully decrypt old ciphertext. === Cross-Domain Capture and Delayed Compare Attack === This is also referred to as a kind of dictionary attack. Similarly, MKTME protects against cross-domain capture-and-compare attacks. Consider the following scenario: * A victim places a secret in memory, at a known physical address * Attacker captures victim’s ciphertext * Attacker gains control of the target physical address, perhaps after the victim’s VM is shut down or its memory reclaimed. * Attacker computes and writes many possible plaintexts until new ciphertext matches content captured previously. Secrets which have low (plaintext) entropy are more vulnerable to this attack because they reduce the number of possible plaintexts an attacker has to compute and write. The attack will not work if attacker and victim uses different keys. === Key Wear-out Attack === Repeated use of an encryption key might be used by an attacker to infer information about the key or the plaintext, weakening the encryption. The higher the bandwidth of the encryption engine, the more vulnerable the key is to wear-out. The MKTME memory encryption hardware works at the speed of the memory bus, which has high bandwidth. Such a weakness has been demonstrated[3] on a theoretical cipher with similar properties as AES-XTS. An attack would take the following steps: * Victim system is using TME with AES-XTS-128 * Attacker repeatedly captures ciphertext/plaintext pairs (can be Performed with online hardware attack like an interposer). * Attacker compels repeated use of the key under attack for a sustained time period without a system reboot[4]. * Attacker discovers a cipertext collision (two plaintexts translating to the same ciphertext) * Attacker can induce controlled modifications to the targeted plaintext by modifying the colliding ciphertext MKTME mitigates key wear-out in two ways: * Keys can be rotated periodically to mitigate wear-out. Since TME keys are generated at boot, rotation of TME keys requires a reboot. In contrast, MKTME allows rotation while the system is booted. An application could implement a policy to rotate keys at a frequency which is not feasible to attack. * In the case that MKTME is used to encrypt two guests’ memory with two different keys, an attack on one guest’s key would not weaken the key used in the second guest. -- [1] https://software.intel.com/sites/default/files/managed/a5/16/Multi-Key-Total-Memory-Encryption-Spec.pdf [2] The MKTME architecture supports up to 16 bits of KeyIDs, so a maximum of 65535 keys on top of the “TME key” at KeyID-0. The first implementation is expected to support 5 bits, making 63 keys available to applications. However, this is not guaranteed. The number of available keys could be reduced if, for instance, additional physical address space is desired over additional KeyIDs. [3] http://web.cs.ucdavis.edu/~rogaway/papers/offsets.pdf [4] This sustained time required for an attack could vary from days to years depending on the attacker’s goals. Alison Schofield (33): x86/pconfig: Set a valid encryption algorithm for all MKTME commands keys/mktme: Introduce a Kernel Key Service for MKTME keys/mktme: Preparse the MKTME key payload keys/mktme: Instantiate and destroy MKTME keys keys/mktme: Move the MKTME payload into a cache aligned structure keys/mktme: Strengthen the entropy of CPU generated MKTME keys keys/mktme: Set up PCONFIG programming targets for MKTME keys keys/mktme: Program MKTME keys into the platform hardware keys/mktme: Set up a percpu_ref_count for MKTME keys keys/mktme: Require CAP_SYS_RESOURCE capability for MKTME keys keys/mktme: Store MKTME payloads if cmdline parameter allows acpi: Remove __init from acpi table parsing functions acpi/hmat: Determine existence of an ACPI HMAT keys/mktme: Require ACPI HMAT to register the MKTME Key Service acpi/hmat: Evaluate topology presented in ACPI HMAT for MKTME keys/mktme: Do not allow key creation in unsafe topologies keys/mktme: Support CPU hotplug for MKTME key service keys/mktme: Find new PCONFIG targets during memory hotplug keys/mktme: Program new PCONFIG targets with MKTME keys keys/mktme: Support memory hotplug for MKTME keys mm: Generalize the mprotect implementation to support extensions syscall/x86: Wire up a system call for MKTME encryption keys x86/mm: Set KeyIDs in encrypted VMAs for MKTME mm: Add the encrypt_mprotect() system call for MKTME x86/mm: Keep reference counts on encrypted VMAs for MKTME mm: Restrict MKTME memory encryption to anonymous VMAs selftests/x86/mktme: Test the MKTME APIs x86/mktme: Overview of Multi-Key Total Memory Encryption x86/mktme: Document the MKTME provided security mitigations x86/mktme: Document the MKTME kernel configuration requirements x86/mktme: Document the MKTME Key Service API x86/mktme: Document the MKTME API for anonymous memory encryption x86/mktme: Demonstration program using the MKTME APIs Jacob Pan (3): iommu/vt-d: Support MKTME in DMA remapping x86/mm: introduce common code for mem encryption x86/mm: Use common code for DMA memory encryption Kai Huang (2): mm, x86: export several MKTME variables kvm, x86, mmu: setup MKTME keyID to spte for given PFN Kirill A. Shutemov (24): mm: Do no merge VMAs with different encryption KeyIDs mm: Add helpers to setup zero page mappings mm/ksm: Do not merge pages with different KeyIDs mm/page_alloc: Unify alloc_hugepage_vma() mm/page_alloc: Handle allocation for encrypted memory mm/khugepaged: Handle encrypted pages x86/mm: Mask out KeyID bits from page table entry pfn x86/mm: Introduce variables to store number, shift and mask of KeyIDs x86/mm: Preserve KeyID on pte_modify() and pgprot_modify() x86/mm: Detect MKTME early x86/mm: Add a helper to retrieve KeyID for a page x86/mm: Add a helper to retrieve KeyID for a VMA x86/mm: Add hooks to allocate and free encrypted pages x86/mm: Map zero pages into encrypted mappings correctly x86/mm: Rename CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING x86/mm: Allow to disable MKTME after enumeration x86/mm: Calculate direct mapping size x86/mm: Implement syncing per-KeyID direct mappings x86/mm: Handle encrypted memory in page_to_virt() and __pa() mm/page_ext: Export lookup_page_ext() symbol mm/rmap: Clear vma->anon_vma on unlink_anon_vmas() x86/mm: Disable MKTME on incompatible platform configurations x86/mm: Disable MKTME if not all system memory supports encryption x86: Introduce CONFIG_X86_INTEL_MKTME .../admin-guide/kernel-parameters.rst | 1 + .../admin-guide/kernel-parameters.txt | 11 + Documentation/x86/mktme/index.rst | 13 + .../x86/mktme/mktme_configuration.rst | 17 + Documentation/x86/mktme/mktme_demo.rst | 53 ++ Documentation/x86/mktme/mktme_encrypt.rst | 57 ++ Documentation/x86/mktme/mktme_keys.rst | 96 +++ Documentation/x86/mktme/mktme_mitigations.rst | 150 ++++ Documentation/x86/mktme/mktme_overview.rst | 57 ++ Documentation/x86/x86_64/mm.txt | 4 + arch/alpha/include/asm/page.h | 2 +- arch/x86/Kconfig | 29 +- arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/x86/include/asm/intel-family.h | 2 + arch/x86/include/asm/intel_pconfig.h | 14 +- arch/x86/include/asm/mem_encrypt.h | 29 + arch/x86/include/asm/mktme.h | 93 +++ arch/x86/include/asm/page.h | 4 + arch/x86/include/asm/page_32.h | 1 + arch/x86/include/asm/page_64.h | 4 +- arch/x86/include/asm/pgtable.h | 19 + arch/x86/include/asm/pgtable_types.h | 23 +- arch/x86/include/asm/setup.h | 6 + arch/x86/kernel/cpu/intel.c | 58 +- arch/x86/kernel/head64.c | 4 + arch/x86/kernel/setup.c | 3 + arch/x86/kvm/mmu.c | 18 +- arch/x86/mm/Makefile | 3 + arch/x86/mm/init_64.c | 68 ++ arch/x86/mm/kaslr.c | 11 +- arch/x86/mm/mem_encrypt_common.c | 28 + arch/x86/mm/mktme.c | 630 ++++++++++++++ drivers/acpi/hmat/hmat.c | 67 ++ drivers/acpi/tables.c | 10 +- drivers/firmware/efi/efi.c | 25 +- drivers/iommu/intel-iommu.c | 29 +- fs/dax.c | 3 +- fs/exec.c | 4 +- fs/userfaultfd.c | 7 +- include/asm-generic/pgtable.h | 8 + include/keys/mktme-type.h | 39 + include/linux/acpi.h | 9 +- include/linux/dma-direct.h | 4 +- include/linux/efi.h | 1 + include/linux/gfp.h | 51 +- include/linux/intel-iommu.h | 9 +- include/linux/mem_encrypt.h | 23 +- include/linux/migrate.h | 14 +- include/linux/mm.h | 27 +- include/linux/page_ext.h | 11 +- include/linux/syscalls.h | 2 + include/uapi/asm-generic/unistd.h | 4 +- kernel/fork.c | 2 + kernel/sys_ni.c | 2 + mm/compaction.c | 3 + mm/huge_memory.c | 6 +- mm/khugepaged.c | 10 + mm/ksm.c | 17 + mm/madvise.c | 2 +- mm/memory.c | 3 +- mm/mempolicy.c | 30 +- mm/migrate.c | 4 +- mm/mlock.c | 2 +- mm/mmap.c | 31 +- mm/mprotect.c | 98 ++- mm/page_alloc.c | 50 ++ mm/page_ext.c | 5 + mm/rmap.c | 4 +- mm/userfaultfd.c | 3 +- security/keys/Makefile | 1 + security/keys/mktme_keys.c | 768 ++++++++++++++++++ .../selftests/x86/mktme/encrypt_tests.c | 433 ++++++++++ .../testing/selftests/x86/mktme/flow_tests.c | 266 ++++++ tools/testing/selftests/x86/mktme/key_tests.c | 526 ++++++++++++ .../testing/selftests/x86/mktme/mktme_test.c | 300 +++++++ 76 files changed, 4301 insertions(+), 122 deletions(-) create mode 100644 Documentation/x86/mktme/index.rst create mode 100644 Documentation/x86/mktme/mktme_configuration.rst create mode 100644 Documentation/x86/mktme/mktme_demo.rst create mode 100644 Documentation/x86/mktme/mktme_encrypt.rst create mode 100644 Documentation/x86/mktme/mktme_keys.rst create mode 100644 Documentation/x86/mktme/mktme_mitigations.rst create mode 100644 Documentation/x86/mktme/mktme_overview.rst create mode 100644 arch/x86/include/asm/mktme.h create mode 100644 arch/x86/mm/mem_encrypt_common.c create mode 100644 arch/x86/mm/mktme.c create mode 100644 include/keys/mktme-type.h create mode 100644 security/keys/mktme_keys.c create mode 100644 tools/testing/selftests/x86/mktme/encrypt_tests.c create mode 100644 tools/testing/selftests/x86/mktme/flow_tests.c create mode 100644 tools/testing/selftests/x86/mktme/key_tests.c create mode 100644 tools/testing/selftests/x86/mktme/mktme_test.c -- 2.20.1
