Tag: l3

Working Set Size (WSS) 的想法

Netflix 的 Brendan Gregg (他比較知名的發明是 Flame Graph) 寫了一篇「How To Measure the Working Set Size on Linux」，他想要量測單位時間內會用到的記憶體區塊大小：

The Working Set Size (WSS) is how much memory an application needs to keep working. Your app may have populated 100 Gbytes of main memory, but only uses 50 Mbytes each second to do its job. That's the working set size. It is used for capacity planning and scalability analysis.

這可以拿來分析這些應用程式是否能夠利用 L1/L2/L3 cache 大幅增加執行速度，於是就可以做成圖，像是這樣：

在 Netflix 這樣人數的公司，需要設計一些有用的指標，另外發展出對應的工具，讓其他人更容易迅速掌握狀況，畢竟不是每個人都有上天下海的能力，遇到狀況可以馬上有頭緒進行 trouble shooting...

在瀏覽器上面用 JavaScript 進行 Side-channel attack

用 JavaScript 就可以攻擊 L3 cache，進而取得資料：「JavaScript CPU cache snooper tells crooks EVERYTHING you do online」。

論文出自「The Spy in the Sandbox – Practical Cache Attacks in Javascript」(PDF) 這篇。

不需要任何外掛或 exploit，就純粹是利用 cache 反應時間的 side-channel attack。另外由於 AMD 的 cache 架構不同，這次的攻擊實作僅對 Intel 有效：

The Intel cache micro-architecture isinclusive– all elements in the L1 cache must also exist in the L2 and L3 caches. Conversely, if a memory element is evicted fromthe L3 cache, it is also immediately evicted from the L2 and L1 cache. It should be noted that the AMD cachemicro-architecture is exclusive, and thus the attacks described in this report are not immediately applicable tothat platform.

這次的攻擊方法真變態...