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Date: Tue, 23 Oct 2018 00:22:28 +0000
From: Ramon de C Valle <rcvalle@...e.com>
To: Andrew Sandoval <ASandoval@...root.com>, "oss-security@...ts.openwall.com"
<oss-security@...ts.openwall.com>
Subject: Re: GCC Compiler Induced Vulnerability - affects
programs compiled with GCC 7 and 8 containing nested functions
> This is already public because oss-security is a public mailing list.
>
> Most GNU/Linux distributions ensure that only very special binaries
> (such as some versions of the Ada compiler) enable executable stacks.
> In our experience, if the toolchain produces a binary that requests an
> executable stack, it is more likely due to manually written assembler
> files without the required stack executability markup section, and not
> due to nested C functions whose address escapes. Without scanning built
> binaries for these discrepancies, such cases could easily be missed.
>
> Please also note that an executable stack is not a vulnerability itself,
> and it is not directly exploitable. (The same applies to the lack of
> Intel CET support in binaries.)
While I agree with that I still think that this extension (or its name) is misleading, see https://lkml.org/lkml/2012/1/9/138. The PF_X flag set in the PT_GNU_STACK segment header or the absence of the PT_GNU_STACK segment header can result in an application unnoticeably having not only the stack, but also all readable virtual memory mappings also executable.
Ramon de C Valle
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