RFC: system-wide default tunables

[Siddhesh Poyarekar]

On 2023-10-17 10:10, Adhemerval Zanella Netto wrote:
> But we already have opt-in security features with glibc.cpu.x86_ibt,
> glibc.cpu.x86_shstk, and glibc.mem.tagging.  At least the x86 ones,
> the default is set by an ELF property (assuming --enable-cet), but
> memory tagging is complete opt-in.
> 
> That's why I think we either need to add some security context on
> system-wide tunables; where the tunable can not be override by user;
> or move the opt-in security tunable to a different mechanism.

Only stricter overrides to systemwide tunables should be allowed, e.g. 
going from enabled memory tagging to disabled memory tagging.  For 
numeric values such as mmap_threshold, we may need to figure out on a 
case by case basis what constitutes "stricter".

Thanks,
Sid