We believe that LVI is principally relevant as an attack by a malicious compromised operating system or hypervisor targeting Intel SGX enclaves. As such, in our current assessment, you should consider LVI and install updates if you are using a recent processor equipped with Intel SGX technology (see "What is Intel SGX" below).

Intel provides a list with all affected products here. SGX is supported on certain Core-family processors from Skylake onwards. The most recent Icelake Core-family processors appear unaffected by LVI. We found that some other recent, acclaimed Meltdown-resistant recent Core-family processors are only potentially vulnerable to LVI-zero-data (aka loads exhibiting zero injection behavior only). Among Atom processors, only older Silvermont/Airmont (without SGX support) are potentially affected.

LVI bypasses all existing mitigations against transient-execution attacks, such as Meltdown, Spectre, Foreshadow, ZombieLoad, RIDL, and Fallout. We show that LVI is especially relevant in the context of Intel SGX, where LVI may arbitrarily hijack transient execution in a victim enclave and ultimately leak arbitrary secrets, breaking confidentiality guarantees in the Intel SGX ecosystem (see "What is Intel SGX" below).

LVI unifies the transient-execution research landscape by applying gadget-driven techniques from the Spectre world to reversely exploit prior Meltdown-type data leakages. LVI furthermore marks the end of transparently patching Meltdown-type processor vulnerabilities in CPU microcode, as LVI necessitates expensive software updates to serialize the processor pipeline and disable speculation after potentially every load operation.

Intel Software Guard eXtensions (SGX) is an innovative processor technology released in 2015 to create isolated environments in the computer's memory, so-called enclaves. SGX acts like a secure vault in the processor itself, combining strong encryption and hardware-level isolation to safeguard enclave programs, and the data they operate on, even against very advanced types of malware that compromise the operating system, hypervisor, or firmware (BIOS).

In our current assessment, we believe that LVI is mainly only relevant to Intel SGX enclaves. However, in the academic paper we showed that none of the ingredients for LVI are unique to Intel SGX and LVI attacks can in principle apply to non-SGX traditional cross-process, cross-virtual-machine, or user-to-kernel environments. We did not succeed in finding any practical LVI gadgets that can be realistically exploited, however, and only explored such non-SGX attacks in synthetic scenarios where we inserted our own LVI gadgets. Hence, we consider non-SGX LVI attacks of mainly academic interest and we agree with Intel's current assessment to not deploy extra mitigations for non-SGX environments, but we encourage future research to further investigate LVI in non-SGX settings (e.g., cross-process and sandboxed environments).

In our current assessment, LVI principally applies only to Intel processors with SGX technology. However, following the argument of symmetry, in in principle any processor that is vulnerable to Meltdown-type data leakage, would also be vulnerable to LVI-style data injection. Some non-Intel processors have been shown to be affected by some variants of Meltdown and Foreshadow. We maintain an up-to-date overview on the website https://transient.fail/ (select Meltdown + vendor ARM or AMD). If an attacker finds software that uses these features in an exploitable way, LVI might still be possible. We encourage future research to investigate the applicability of LVI to non-Intel CPUs.

LVI is short for Load Value Injection. Simplified, it turns Meltdown-type attacks around to inject data into an application instead of leaking data. Under certain circumstances, an attacker can inject arbitrary data, replacing the value an application loads from memory. The application uses this value for a short period of time until detecting the mistake, and rolling back all operations. However, in this short period, an attacker can arbitrarily hijack the control and data flow.

For a systematic overview of all known attacks to date, we refer to https://transient.fail/.

No, these are vulnerabilities in the processor. While software workarounds exist, the root cause for LVI cannot be eradicated in software. However, new CPUs will contain hardware fixes.

Future CPUs will contain silicon fixes to mitigate LVI directly in hardware. At least for SGX enclaves a short-term solution is needed to mitigate LVI on current, widely deployed systems. In contrast to previous Meltdown-type attacks, processor microcode updates to flush affected buffers are no longer sufficient. Instead, complementary to existing Spectre software mitigations, LVI necessitates compiler patches to insert explicit lfence speculation barriers which serialize the processor pipeline after potentially every vulnerable load instruction. Additionally and even worse, due to implicit loads, certain instructions have to be blacklisted, including the ubiquitous x86 ret instruction.

Intel is releasing an update for the Intel SGX SDK to assist SGX application providers in updating their enclave code. For other guidance, please review Intel’s white paper here. For more information on trusted computing base recovery in the Intel SGX ecosystem, see here.

Depending on the application and optimization strategy, we observe extensive overheads of factor 2 to 19 for prototype implementations of the full mitigation. However, we expect that real-world performance overheads for Intel SGX will depend on the specific use case. We refer to our technical paper and the graphs below for a more detailed performance evaluation on SPEC and OpenSSL.

In the academic paper, we propose an unambiguous naming scheme to reason about and distinguish LVI variants, following the extended transient-execution attack classification tree at https://transient.fail/. Particularly, in a first level, we distinguish the fault or assist type triggering the transient execution, and at a second level we specify the microarchitectural buffer which is used as the injection source. We show the resulting two-level LVI classification tree below (red leaves are demonstrated attacks, green leaves are already mitigated by existing defenses). Note that, much like in the perpendicular Spectre class of attacks, not all CPUs from all vendors might be susceptible to all of these variants.

We do not have any data on this. The exploitation might not leave any traces in traditional log files.

Yes, there is an academic research paper that can be downloaded here and will be presented at the 41th IEEE Symposium on Security and Privacy (IEEE S&P'20) in May 2020.

CVE-2020-0551 is the official reference to LVI. CVE is the Standard for Information Security Vulnerability Names maintained by MITRE.

The logo is free to use, rights waived via CC0. Logo designed by Natascha Eibl.

For educational purposes, we released elementary example LVI attack applications as part of the open-source SGX-Step enclave side-channel attack framework available on GitHub. The examples focus only on demonstrating injection of dummy attacker data from various microarchitectural buffers and illustrating LVI-based transient control flow hijacking in a victim enclave.