Date: Thu, 07 May 2015 16:47:16 +0200 From: Hector Marco-Gisbert <hecmargi@....es> To: oss-security@...ts.openwall.com CC: Ismael Ripoll <iripoll@...ca.upv.es> Subject: Re: CVE-Request: AMD Bulldozer Linux ASLR weakness: Reducing entropy by 87.5%. Hi, PaX solution has actually 16 random bits for mmap objects in 32bit systems on non affected systems. On affected systems the random bits are degraded to 2^13. Unfortunately, depending on the PaX Kernel configuration sequence, some features may not be enabled. There are sequences of PaX configuration which does not give the expected result. The configuration sequence that results in a miss-configured system is: 1.- Starting from a clean Linux tree with PaX patch applied. 2.- Enabled the "Grsecurity" option (which sets "Security Method" to "Custom") and compile&test: Observed mmap entropy: 2^5 (as expected). 3.- Then set "Security Method" to "Automatic" (which sets "Required Priorities" to "Performance") and compile&test: Observed mmap entropy: 2^5. 4.- Last test: select "Security" on the "Required Priorities" option and compile&test: Observed mmap entropy: 2^5. 5.- At this point, it seems that the "Required Priorities" option has no effect, that is, switching from "Performance" to "Security" or the other way around (as may times as desired) does not enable/disable the expected features, including the mmap randomization. If steps 2 and 3, or 2 and 4 are configured at once (without exiting from the menuconfig), then the system gets properly configured. It seems that something in the PaX Kconfig files are not properly done. Could anyone check it ? So, if you are using PaX, it worth to ensure that you are not losing any PaX feature. -- Hector Marco-Gisbert @ http://hmarco.org/ Cyber Security Researcher @ http://cybersecurity.upv.es Universitat Politècnica de València (Spain)
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