The __KERNEL__ #define

[John Richard Moser]

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Recently there has been talk of splitting up include/linux to obsolete
the __KERNEL__ define.  I would like to request that __KERNEL__ remain
defined in the kernel build process and in module building.

A modified specs file on Gentoo enables -fstack-protector{,-all} in gcc,
two switches added by a patch[1][2] to gcc made by Etoh and Yoda of the
IBM Tokyo Research Labs.  This patch relies on several symbols not
defined in the kernel to do a type of artificial bounds checking,
preventing stack-based buffer overflows from being utilized in security
exploits.  It was determined that this is non-useful in the kernel
(although possibly more research should be done-- is it worth it to
panic when we think there's a kernel-level exploit occuring?), and so
the specs file does not enable these if __KERNEL__ is defined.

The specs file also generates PIE-by-default executables, and disables
this functionality if __KERNEL__ is defined; so if it is determined that
~ SSP in the kernel would be useful, this define is still needed.  In
general it is in itself harmless and should stay as an indicator.

The Hardened Debian project is going to implement a similar specs file
alteration, which may be used in Ubuntu and Debian.

[1] trl.ibm.com/projects/security/ssp/
[2] trl.ibm.com/projects/security/ssp/main.html (paper)

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