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Ubuntu 開始更新 Kernel 了...

這波 CPU 安全問題,UbuntuLinux Kernel 的更新計畫 (workaround patch) 放在「Information Leak via speculative execution side channel attacks (CVE-2017-5715, CVE-2017-5753, CVE-2017-5754 aka Spectre and Meltdown)」這邊。

不是所有版本的 kernel 都有更新,像是我之前跑 4.10 發現這次沒在清單內,就換成 linux-image-generic-hwe-16.04-edge 了... 換完後需要再裝 linux-headers-generic-hwe-16.04-edge,然後把舊的 kernel 都清乾淨,最後 nvidia-387 需要重新編過。

這次苦哈哈啊...

把自動播放影片的功能關掉...

一堆國外新聞網站超愛這套,這不是 Flash 時代的搞法嗎,怎麼現在還這樣搞啊... 在 Google Chrome 內建的設定就可以關掉了,先進入 chrome://flags,然後選擇「Document activation is required.」:

中文版的 Chrome 不知道是翻成什麼,就自己翻譯猜一下吧...

Intel CPU + AMD GPU 合一的的系統

先前就有看到 Intel 要與 AMD 合作,將 Intel CPU + AMD GPU 整合在一起以對抗 Nvidia,現在看到 HP 推出對應的筆電了:「HP’s new 15-inch Spectre x360 uses the hybrid Intel/AMD processor」。

不過名字剛好跟最近的安全漏洞撞到了 XDDD (所以才想寫 XDDD)

The new Spectre x360 15 is one of the first systems to be announced that uses the new Kaby Lake-G processors from Intel. These processors combine an Intel CPU (with its own integrated GPU) with an AMD GPU, all within a single package.


出自「Kaby Lake-G unveiled: Intel CPU, AMD GPU, Nvidia-beating performance」。

這種合作的仗打不打的動呢... 不怎麼看好就是了 :o

JVM 的各種調校

看到「JVM Anatomy Park」這篇,作者是 Red HatOpenJDK 團隊的人,寫了二十則與 JVM 效能相關的主題,裡面提到每則大約花五到十分鐘可以看完,不過我覺得應該會再久一點 (需要翻資料交叉查)。

除了網頁版外,也提供 EPUB、MOBI 與 PDF 格式可以下載。

都是講效能相關的,從不同角度看。以第一個 Lock Coarsening and Loops 來說,已知這段程式碼:

synchronized (obj) {
  // statements 1
}
synchronized (obj) {
  // statements 2
}

會被轉換成這樣等效的程式碼:

synchronized (obj) {
  // statements 1
  // statements 2
}

作者就問了,那這樣的話,這段:

for (...) {
  synchronized (obj) {
    // something
  }
}

會不會轉成這段呢:

synchronized (this) {
  for (...) {
     // something
  }
}

答案是不會,但可以橋:

While lock coarsening does not work on the entire loop, another loop optimization — loop unrolling — sets up the stage for the regular lock coarsening, once the intermediate representation starts to look as if there are N adjacent lock-unlock sequences. This reaps the performance benefits, and helps to limit the scope of coarsening, to avoid over-coarsening over fat loops.

就大概是這樣的主題 XD 每天看個一兩篇慢慢消化還不錯...

Elsevier 讓德國的研究機構在還沒有續約的情況下繼續使用

德國的研究機構在 2017 年年底前,也就是與 Elsevier 的合約到期前,還是沒有續約,但 Elsevier 決定還是先繼續提供服務,暫時性的為期一年,繼續談判:

The Dutch publishing giant Elsevier has granted uninterrupted access to its paywalled journals for researchers at around 200 German universities and research institutes that had refused to renew their individual subscriptions at the end of 2017.

The institutions had formed a consortium to negotiate a nationwide licence with the publisher. They sought a collective deal that would give most scientists in Germany full online access to about 2,500 journals at about half the price that individual libraries have paid in the past. But talks broke down and, by the end of 2017, no deal had been agreed. Elsevier now says that it will allow the country’s scientists to access its paywalled journals without a contract until a national agreement is hammered out.

Elsevier 會這樣做主要是要避免讓德國的學術機構發現「沒有 Elsevier 其實也活的很好」。而不少研究人員已經知道這件事情,在大多數的情況下都有 Elsevier 的替代方案,不需要浪費錢簽那麼貴的費用:

Günter Ziegler, a mathematician at the Free University of Berlin and a member of the consortium's negotiating team, says that German researchers have the upper hand in the negotiations. “Most papers are now freely available somewhere on the Internet, or else you might choose to work with preprint versions,” he says. “Clearly our negotiating position is strong. It is not clear that we want or need a paid extension of the old contracts.”

替代方案有幾個方面,像是自由開放下載的 arXiv 愈來愈受到重視,很多研究者都會把投稿的論文在上面放一份 pre-print 版本 (甚至會更新),而且近年來有些知名的證明只放在上面 (像是 Poincaré conjecture)。而且放在人家家裡比放在自己網站來的簡單 (不需要自己維護),這都使得 arXiv 變成學術界新的標準平台。

除了 arXiv 外,其他領域也有自己習慣的平台。像是密碼學這邊的「Cryptology ePrint Archive」也運作很久了。

除了找平台外,放在自家網站上的論文 (通常是學校或是學術機構的個人空間),也因為搜尋引擎的發達,使得大家更容易找到對應檔案可以下載。

而且更直接的攻擊性網站是 Sci-Hub,讓大家從 paywall 下載後丟上去公開讓人搜尋。雖然因為常常被封鎖的原因而常常在換網址,不過透過 Tor Browser (或是自己設定 Tor Proxy) 存取他們的 Hidden Service 就應該沒這個問題。

希望德國可以撐下去,證明其實已經不需要 Elsevier...

Ubuntu 下調整滑鼠的速度...

換了一隻滑鼠後,發現速度已經調到最慢了,但還是感覺太快:

這時候就得調其他東西了,我是參考「Fix Mouse Sensitivity in Ubuntu 16.04」這邊的說明來調整的。測過 xset 會動後,把檔案丟到 ~/.config/autostart/mouse.desktop 裡面讓他登入後生效:

[Desktop Entry]
Name=Decrease mouse sensitivity
Exec=xset m 1/2 8
Type=Application
Comment[en_US]=Use xset to set mouse params
Comment=Use xset to set mouse params

這樣習慣一些...

Amazon CloudWatch Logs 換 SSL Certificate 的 CA

收到標題是「Upcoming Changes to SSL Certificates in Amazon CloudWatch Logs」的信件,說明 Amazon CloudWatch Logs 要換 SSL Certificate 的 CA,看起來是要換成自家的:

We will be updating the certificate authority (CA) for the certificates used by Amazon CloudWatch Logs domain(s), between 8 January 2018 and 22 January 2018. After the updates complete, the SSL/TLS certificates used by Amazon CloudWatch Logs will be issued by Amazon Trust Services (ATS), the same certificate authority (CA) used by AWS Certificate Manager.

然後有提到 cross-sign 的部份,有透過 Starfield 的 Root CA 簽,所以只要下面有任何一個有在 Root CA store 裡面就應該會信任:

The update means that customers accessing AWS webpages via HTTPS (for example, the Amazon CloudWatch Console, customer portal, or homepage) or accessing Amazon CloudWatch Logs API endpoints, whether through browsers or programmatically, will need to update the trusted CA list on their client machines if they do not already support any of the following CAs:
- "Amazon Root CA 1"
- "Starfield Services Root Certificate Authority - G2"
- "Starfield Class 2 Certification Authority"

另外條列出有哪些 API endpoint 會改變:

This upgrade notice covers the following endpoints:
logs.ap-northeast-1.amazonaws.com
logs.ap-northeast-2.amazonaws.com
logs.ap-south-1.amazonaws.com
logs.ap-southeast-1.amazonaws.com
logs.ap-southeast-2.amazonaws.com
logs.ca-central-1.amazonaws.com
logs.eu-central-1.amazonaws.com
logs.eu-west-1.amazonaws.com
logs.eu-west-2.amazonaws.com
logs.eu-west-3.amazonaws.com
logs.us-east-1.amazonaws.com
logs.us-east-2.amazonaws.com
logs.us-west-1.amazonaws.com
logs.us-west-2.amazonaws.com
logs.sa-east-1.amazonaws.com

然後也列出了有哪些系統「應該」會支援:

* Operating Systems With ATS Support
- Microsoft Windows versions that have January 2005 or later updates installed, Windows Vista, Windows 7, Windows Server 2008, and newer versions
- Mac OS X 10.4 with Java for Mac OS X 10.4 Release 5, Mac OS X 10.5 and newer versions
- Red Hat Enterprise Linux 5 (March 2007), Linux 6, and Linux 7 and CentOS 5, CentOS 6, and CentOS 7
- Ubuntu 8.10
- Debian 5.0
- Amazon Linux (all versions)
- Java 1.4.2_12, Java 5 update 2, and all newer versions, including Java 6, Java 7, and Java 8

不過沒看到 Windows XP 耶,不知道是怎樣 XD

Fortnite 看起來沒上 Auto Scaling?(或是沒正確設好?)

Fortnite 遊戲的伺服器放在 AWS 上,看起來這波 Meltdown 的安全更新 (KPTI) 造成非常大的 overhead:

不過看起來出了問題:

We wanted to provide a bit more context for the most recent login issues and service instability. All of our cloud services are affected by updates required to mitigate the Meltdown vulnerability. We heavily rely on cloud services to run our back-end and we may experience further service issues due to ongoing updates.

最有可能的是把 AWS 當作一般的 VPS 在用,另外一種可能是有部份內部服務沒有 scale,造成上了 KPTI 後 overhead 增加,就卡住了...

讀書時間:Meltdown 的攻擊方式

Meltdown 的論文可以在「Meltdown (PDF)」這邊看到。這個漏洞在 Intel 的 CPU 上影響最大,而在 AMD 是不受影響的。其他平台有零星的消息,不過不像 Intel 是這十五年來所有的 CPU 都中獎... (從 Pentium 4 以及之後的所有 CPU)

Meltdown 是基於這些前提,而達到記憶體任意位置的 memory dump:

  • 支援 µOP 方式的 out-of-order execution 以及當失敗時的 rollback 機制。
  • 因為 cache 機制造成的 side channel information leak。
  • 在 out-of-order execution 時對記憶體存取的 permission check 失效。

out-of-order execution 在大學時的計算機組織應該都會提到,不過我印象中當時只講「在確認不相干的指令才會有 out-of-order」。而現代 CPU 做的更深入,包括了兩個部份:

  • 第一個是 µOP 方式,將每個 assembly 拆成更細的 micro-operation,後面的 out-of-order execution 是對 µOP 做。
  • 第二個是可以先執行下去,如果發現搞錯了再 rollback。

像是下面的 access() 理論上不應該被執行到,但現代的 out-of-order execution 會讓 CPU 有機會先跑後面的指令,最後發現不該被執行到後,再將 register 與 memory 的資料 rollback 回來:

而 Meltdown 把後面不應該執行到 code 放上這段程式碼 (這是 Intel syntax assembly):

其中 mov al, byte [rcx] 應該要做記憶體檢查,確認使用者是否有權限存取那個位置。但這邊因為連記憶體檢查也拆成 µOP 平行跑,而產生 race condition:

Meltdown is some form of race condition between the fetch of a memory address and the corresponding permission check for this address.

而這導致後面這段不該被執行到的程式碼會先讀到資料放進 al register 裡。然後再去存取某個記憶體位置造成某塊記憶體位置被讀到 cache 裡。

造成 cache 內的資料改變後,就可以透過 FLUSH+RELOAD 技巧 (side channel) 而得知這段程式碼讀了哪一塊資料 (參考之前寫的「Meltdown 與 Spectre 都有用到的 FLUSH+RELOAD」),於是就能夠推出 al 的值...

而 Meltdown 在 mov al, byte [rcx] 這邊之所以可以成立,另外一個需要突破的地方是 [rcx]。這邊 [rcx] 存取時就算沒有權限檢查,在 virtual address 轉成 physical address 時應該會遇到問題?

原因是 LinuxOS X 上有 direct-physical map 的機制,會把整塊 physical memory 對應到 virtual memory 的固定位置上,這些位置不會再發給 user space 使用,所以是通的:

On Linux and OS X, this is done via a direct-physical map, i.e., the entire physical memory is directly mapped to a pre-defined virtual address (cf. Figure 2).

而在 Windows 上則是比較複雜,但大部分的 physical memory 都有對應到 kernel address space,而每個 process 裡面也都還是有完整的 kernel address space (只是受到權限控制),所以 Meltdown 的攻擊仍然有效:

Instead of a direct-physical map, Windows maintains a multiple so-called paged pools, non-paged pools, and the system cache. These pools are virtual memory regions in the kernel address space mapping physical pages to virtual addresses which are either required to remain in the memory (non-paged pool) or can be removed from the memory because a copy is already stored on the disk (paged pool). The system cache further contains mappings of all file-backed pages. Combined, these memory pools will typically map a large fraction of the physical memory into the kernel address space of every process.

這也是 workaround patch「Kernel page-table isolation」的原理 (看名字大概就知道方向了),藉由將 kernel 與 user 的區塊拆開來打掉 Meltdown 的攻擊途徑。

而 AMD 的硬體則是因為 mov al, byte [rcx] 這邊權限的檢查並沒有放進 out-of-order execution,所以就避開了 Meltdown 攻擊中很重要的一環。

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