Le 09/01/2026 à 07:49, Shrikanth Hegde a écrit :
Recently stumbled upon these kuap warnings. This happens with
preempt=full/lazy kernel with function tracing enabled. What irked
me was kernel compilation was getting failed when i had tracing
enabled. It doesn't fail everytime. While running stress-ng memory class
it threw same warnings. So that helped to narrow it down.
So one possible way is to disable tracing for these enter/exit
vmx_usercopy. That seems to fix the bug/warnings. But that will make
them as non trace-able. If there is a better way to fix these warning while
keeping them as trace-able, please let me know.
Anyone with insights on amr, vmx and tracing, please advise.
The main principle with KUAP is to not call subfunctions once userspace
access enabled. There are a few exceptions like __copy_tofrom_user()
that are allowed in order to optimise large copies. However this needs
to be handled very carefully, and in principle we don't expect
__copy_tofrom_user() to call other functions.
So it might require wider rework but we should narrow as much as
possible the period during which access to userspace is opened, with
something like:
raw_coy_to_user_power7()
{
enter_vmx_usercopy();
allow_write_to_user(to, n);
ret = __copy_tofrom_user_power7();
prevent_write_to_user(to, n);
exit_vmx_usercopy();
return ret;
}
raw_copy_to_user()
{
if (cpu_has_feature(CPU_FTR_VMX_COPY))
raw_copy_to_user_power7();
allow_write_to_user(to, n);
ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
prevent_write_to_user(to, n);
return ret;
}
