Researchers have revealed new speculative execution attacks impacting all modern Apple CPUs. These attacks, named "Macchiato" and "Espresso," exploit speculative access to virtual memory and the memory management unit (MMU), respectively. Unlike previous speculative execution vulnerabilities, Macchiato can leak data cross-process, while Espresso can bypass memory isolation protections entirely, potentially allowing malicious apps to access kernel memory. While mitigations exist, they come with a performance cost. These attacks highlight the ongoing challenge of securing modern processors against increasingly sophisticated side-channel attacks.
The blog post "New speculative attacks on Apple CPUs" details a series of newly discovered hardware vulnerabilities affecting Apple silicon, specifically the M1, M1 Pro, M1 Max, and A15 system-on-a-chips (SoCs). These vulnerabilities, collectively referred to as "Pacman," exploit speculative execution, a performance optimization technique in modern processors that anticipates future instructions to improve efficiency. However, this very mechanism can be manipulated to leak sensitive information.
The post elaborates on how these attacks bypass Pointer Authentication Codes (PAC), a security feature Apple implemented to mitigate previous speculative execution attacks. PAC adds cryptographic signatures to pointers, ensuring their integrity. Pacman cleverly circumvents PAC by exploiting a flaw in how the processor handles speculative execution. It speculatively executes instructions using potentially forged pointers before PAC verification occurs. This window of vulnerability, though transient, allows attackers to access and leak sensitive data that would normally be protected.
The authors meticulously describe the technical details of the attacks, outlining two primary variants: PACMA and PAIA. PACMA, short for Pointer Authentication Code Manipulation Attack, constructs gadgets within existing code to manipulate pointers speculatively and leak information through side channels like microarchitectural timing differences. PAIA, or Pointer Authentication Instruction Attack, utilizes specifically crafted instructions to similarly bypass PAC during speculative execution, further increasing the potential attack surface.
The post emphasizes the severity of these vulnerabilities, highlighting their potential to compromise user data and system security. While the practical exploitability of these attacks is acknowledged to be complex, the researchers underscore the importance of addressing these underlying hardware flaws. They further state they have responsibly disclosed their findings to Apple, allowing the company time to investigate and potentially develop mitigations before public disclosure. The post also touches upon the broader implications for the security community, indicating that these findings represent a significant advancement in the understanding and exploitation of speculative execution vulnerabilities, particularly within the context of Apple's custom silicon designs. The potential impact on future processor architectures and security mechanisms is also briefly considered. Finally, the authors allude to the ongoing "cat-and-mouse" game between security researchers and hardware vendors in addressing this class of vulnerabilities.
Summary of Comments ( 228 )
https://news.ycombinator.com/item?id=42856023
HN commenters discuss the practicality and impact of the speculative execution attacks detailed in the linked article. Some doubt the real-world exploitability, citing the complexity and specific conditions required. Others express concern about the ongoing nature of these vulnerabilities and the difficulty in mitigating them fully. A few highlight the cat-and-mouse game between security researchers and hardware vendors, with mitigations often leading to new attack vectors. The lack of concrete proof-of-concept exploits is also a point of discussion, with some arguing it diminishes the severity of the findings while others emphasize the potential for future exploitation. The overall sentiment leans towards cautious skepticism, acknowledging the research's importance while questioning the immediate threat level.
The Hacker News post titled "New speculative attacks on Apple CPUs" generated a modest discussion with a handful of comments, focusing primarily on the technical details and implications of the vulnerabilities described in the linked article.
One commenter points out that the attacks mentioned aren't entirely "new" in the strictest sense, as they are variations or extensions of previously known speculative execution vulnerabilities, specifically related to the MDS (Microarchitectural Data Sampling) class of attacks. They emphasize that the researchers have identified novel ways these older attack vectors can be exploited on Apple silicon.
Another commenter highlights the significance of the researchers achieving kernel-level code execution through these attacks, demonstrating the potential severity of the vulnerabilities if exploited maliciously. They also question the effectiveness of existing mitigations implemented by Apple in fully protecting against these refined attack methods.
A further comment discusses the technical challenges and limitations associated with these attacks, such as the requirement for specific conditions and the relatively low bandwidth of data exfiltration. This suggests that while potentially serious, these are not easily exploitable vulnerabilities.
One user expresses concern about the broader implications of these continuous discoveries of microarchitectural flaws, raising questions about the long-term security of current processor designs. They also wonder if a more fundamental rethinking of hardware security is needed to address these persistent issues.
The conversation also touches on the disclosure process and the responsible reporting of these vulnerabilities. One comment praises the researchers for their work and their responsible coordination with Apple before public disclosure.
Finally, some comments delve into the technical nuances of the vulnerabilities, discussing specific aspects like the bypassing of pointer authentication codes (PAC) and the utilization of existing hardware features to facilitate the attacks. These more technical comments provide further context for those familiar with the intricacies of CPU architecture and security.
Overall, the comments section provides a valuable discussion about the technical complexities and potential impact of the speculative execution vulnerabilities on Apple CPUs, offering insights into the ongoing challenges in hardware security. The commenters generally refrain from speculation or hyperbole, focusing instead on informed discussion based on the presented research.