Re: [Qemu-devel] [PATCH 3/7] configure: add CET support

[Paolo Bonzini]

On 13/03/19 14:31, Florian Weimer wrote:
> * Paolo Bonzini:
> 
>> Actually I might change it to cf-protection, since that's what the GCC
>> flag is named.
> 
> The GCC flag is supposed to generic, so that it can be used for similar
> features other architectures might provide.  Your code looks rather
> x86-centric to me, so CET seems appropriate here.

The configure option is generic.  When enabled, the Makefiles will
*disable* CET features selectively on object files that do not support
that feature, and the disabled feature will propagate to the binary.

Even without any further target-specific patches, user-mode emulation
binaries will always have shadow stacks, because they don't need
coroutines and don't include the problematic util/coroutine-ucontext.o
object file.  Likewise, system-mode emulation binaries will have
indirect branch tracking if built without binary translation support
(i.e. Xen/KVM only).

What the next patches do is to enable the full set of control flow
protections on all binaries on Intel targets.  However, a subset can be
made available without any target-specific code, and that part is
supposed to be generic just like GCC's -fcf-protection flag.

And yes, all this probably should go in more verbose commit messages...

Paolo