Over the past three decades, cache side channels evolved from specialized attacks on cryptographic implementations to generic techniques (e.g., Flush+Reload and Page Cache Attacks) on general-purpose operations. During the last decade, SSDs became the de facto standard persistent storage, where capacity is not the highest priority. In this paper, we present a novel cache side channel, targeting the host-memory buffer (HMB) used by mid-range SSDs to cache translations from logical page addresses to physical page addresses. We demonstrate that, compared to page cache attacks, our attacks are significantly faster as we can evict reliably in only 22 ms. Consequently, we propose a hybrid attack, using the slow page cache eviction as little as possible and using the HMB side channel for our main attack. We evaluate the HMB side channel in four practical attacks: First, we evaluate the capacity of the HMB side channel in a covert channel scenario, achieving up to 8.3 kbit/s channel capacity. Second, we demonstrate a UI redress attack using the HMB side channel, where the fake UI element covers the real one within 100 ms. Third, given that multiple pages from different security contexts are translated through the same HMB entry, we demonstrate blind templating attacks, that allow to spy on accesses to arbitrary other files whose translation is co-located in the same HMB entry. We use this to demonstrate a cross-VM covert channel and a remote side channel where an unprivileged process without network access exfiltrates data to a remote system over the network, through the HMB side channel by using an nginx web server as a confused deputy.
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