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Date: Wed, 10 Jul 2024 17:39:04 -0400
From: Will Dormann <will.dormann@...lygence.com>
To: oss-security@...ts.openwall.com
Subject: Re: ASLRn't is still alive and well on x86 kernels,
 despite CVE-2024-26621 patch

On 7/10/24 4:54 PM, Yves-Alexis Perez wrote:
> On Mon, 2024-07-08 at 12:37 -0400, Will Dormann wrote:
>>    - Modern (e.g. 6.x kernel) x86 platforms load a large-enough libc at
>> the same address every time. (i.e. no practical ASLR -- "ASLRn't")
>>    -  Modern (e.g. 6.x kernel and large-enough libc) x86_64 platforms
>> running 32-bit code will load a large-enough library at the same address
>> every time.
>>    - Modern x86_64 systems with the CVE-2024-26621 patch will randomize
>> the load address of large libraries loaded by 32-bit apps.
>>    - Modern x86 systems with the CVE-2024-26621 patch will NOT ranzomize
>> the load address of large libraries.  (i.e. is still vulnerable to
>> "ASLRn't" despite the patch)
> 
> Hey,
> 
> I'm testing on my Debian sid laptop with Linux kernel 6.9.7-1. This is amd64
> but running test-mmap built with -m32, and I get:
> 
> for i in {0..10}; do ./test-mmap < zeros; done
> mmap(NULL, 2097152, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 0, 0) = 0xf7df3000
> mmap(NULL, 2097152, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 0, 0) = 0xf7d98000
> mmap(NULL, 2097152, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 0, 0) = 0xf7d6f000



Linux 6.9.7 was released in June2024, and the patches for CVE-2024-26621 
went in months before that.  This behavior matches my 3rd bullet point 
above, so I think everything is as expected here.  ("... will randomize 
the load address of large libraries loaded by 32-bit apps.")

If you want to see the lack of randomization, try the test with an x86 
kernel, not amd64.



-WD

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