svn commit: r367577 - in head: share/mk sys/conf tools/build/options

[Shawn Webb]

On Tue, Nov 10, 2020 at 07:17:29PM +0000, Brooks Davis wrote:
> On Tue, Nov 10, 2020 at 07:15:14PM +0000, Brooks Davis wrote:
> > Author: brooks
> > Date: Tue Nov 10 19:15:13 2020
> > New Revision: 367577
> > URL: https://svnweb.freebsd.org/changeset/base/367577
> > 
> > Log:
> >   Support initializing stack variables on function entry
> >   
> >   There are two options:
> >    - WITH_INIT_ALL_ZERO: Zero all variables on the stack.
> >    - WITH_INIT_ALL_PATTERN: Initialize variables with well-defined patterns.
> >   
> >   The exact pattern are a compiler implementation detail and vary by type.
> >   They are somewhat documented in the LLVM commit message:
> >   https://reviews.llvm.org/rL349442
> >   I've used WITH_INIT_ALL_* to match Microsoft's InitAll feature rather
> >   than naming them after the LLVM specific compiler flags.
> >   
> >   In a range of consumer products, options like these are used in
> >   both debug and production builds with debugs builds using patterns
> >   (intended to provoke crashes on use of uninitialized values) and
> >   production using zeros (deemed more likely to lead to harmless
> >   misbehavior or NULL-pointer dereferences).
> 
> We've tested this extensively in CheriBSD on RISC-V, in the wild it's
> probably most tested on Arm64 and x86.
> 
> Despite the silly compiler flag you'll spot in the code, the zeroing
> option isn't going away in practice as Apple, Google, and Microsoft all
> ship with this feature in some of their products.

HardenedBSD's testing of this last year on amd64 have (privately)
shown the feature to really hinder performance on more complex
applications (like when applied to clang/lld). A build of base
without init all zero applied to clang/lld would take around 1.5
hours on my system. A build with it applied to clang/lld took around
four hours, if my memory serves correctly. I would probably advise
against applying it system-wide. But YMMV.

Thanks,

-- 
Shawn Webb
Cofounder / Security Engineer
HardenedBSD

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