KASAN: Disable the sanitizer in stack_capture()

[markj]

Summary

When unwinding the stack we may descend into a poisoned region of the
kernel stack. I don't see a good way to handle this except to disable
the sanitizer entirely.

Define __nosanitizeaddress depending on whether we're in the kernel or
not, since KASAN and ASAN require different attributes. Add
__nosanitizememory while I'm here.

A further complication is that clang raises an error if
no_sanitize("kernel-address") is applied to a global variable rather
than a function:

error: 'no_sanitize' attribute only applies to functions and methods

So, modify linker_set.h to apply the attribute only if we're not in the
kernel.

[kib]

sys/x86/x86/stack_machdep.c

73

I have no idea what is going on there, but don't all called functions require the same handling, e.g. stack_zero? Is it happen to work because struct stack itself is 'not poisoned'?

[markj]

sys/x86/x86/stack_machdep.c

73

stack_zero() is fine, it's the inline dereference of the frame pointer that potentially causes problems.

[kib]

Mostly on principle "I do not see anything wrong"