Tracking Oracle Database Binaries files changes

The Linux Audit system provides a way to determine the violator of the security policy and the actions they performed such as tracking malicious changes on the oracle executable.

Using Linux Audit system we can basically do the following activities :

  • Watching file access
  • Monitoring system calls
  • Recording commands run by a user
  • Recording security events

In this short blog post i will show how we can easily use it to catch changes in “./bin” directory.

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Using LD_PRELOAD to implement a hidden trojan in an oracle database

In one of my previous post  i showed how we can inject a backdoor in an ORACLE database based on Dennis Yurichev findings.The described method required the modification of the oracle executable files.  Few days ago Rodrigo Jorge shared a blog post explaining how we can add another layer of security to the oracle binaries files to protect them against improper changes. That motivated me to check if i still can implement the hidden Trojan without modifying the oracle executable files ?

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Playing with oracle DB 18c on-premises before official release

Rodrigo Jorge has already explained a great way to install and play with Oracle 18c DB instance on-premises using Exadata binaries downloaded from edelivery. The basic idea is to install the oracle exadata binaries and before creating the database replace the library “libserver18.a” with the  version gotten from an oracle cloud instance  (Using Oracle Cloud trial account). And that’s it !

But for those like me that don’t have an international credit card required to create an Oracle Cloud trial account  (Yes i don’t have one 😦 ) or don’t want to create one  ! How to proceed to get a copy of this working libserver18.a library ? May be ask one of the oracle folks to upload it to somewhere and hope that there is no backdoor on it :p  or just try to hack it your self 😀

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Tracing PL/SQL subprogram calls with parameters values [Dynamic tracing]

The purpose of this blog post is demonstrate again the power of Linux dynamic tracing/instrumentation tools.

In my last blog post Enhancing DBMS_OUTPUT using systemtap i showed how we can track  the parameter values passed to “dbms_output.put_line” routine using systemtap.That was a very simple example because we already know the type of the arguments passed (a simple VARCHAR2) and also because there is only ONE parameter.

Tracking PL/SQL routine calls arguments using dynamic tracing utility like perf or systemtap can become quite complex depending on many things like :

  • Argument types
  • Argument number
  • Argument passed  By Value/By reference
  • Subprograms type (nested/package/standalone subprogram)
  • Optimization level (ex: inlining of call of procedure)

Time for the serious stuff  with dynamic tracing tool PERF ! 

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Playing with SLOB and hardware prefetchers ! Are they effective ?

Hardware prefetching can reduce the effective memory latency for data and instruction accesses improving performance (reduces cache-miss exposure) but it can also cause  performance degradation in some cases.  (For more information see here )
My current processor intel skylake i5-6500 support 4 types of h/w prefetchers for prefetching data. There are 2 prefetchers associated with L1-data cache (also known as DCU) and 2 prefetchers associated with L2 cache.This hardware prefetcher can be enable/disabled using Model Specific Register (MSR)
Let’s test how effective they are using SLOB !

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Memory bandwidth vs latency response curve

Memory bound applications are sensitive to memory latency and bandwidth that’s why it’s important to measure and monitor them.Even if this two concepts are often described  independently they are inherently interrelated.

According to Bruce Jacob in ” The memory system: you can’t avoid it, you can’t ignore it, you can’t fake it” the bandwidth vs latency response curve for a system has three regions.

  • Constant region: The latency response is fairly constant for the first 40% of the sustained bandwidth.
  • Linear region:  In between 40% to 80% of the sustained bandwidth, the latency response increases almost linearly with the bandwidth demand of the system due to contention overhead by numerous memory requests.
  • Exponential region:  Between 80% to 100% of the sustained bandwidth,  the memory latency is dominated by the contention latency which can be as much as twice the idle latency or more.
  • Maximum sustained bandwidth :  Is 65% to 75% of the theoretical maximum bandwidth.
 Armed with Intel Memory Latency Checker (MLC) let’s check our current system !

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