RE: [PATCH v6 1/3] x86/speculation: apply IBPB more strictly to avoid cross-process data leak

[Schaufler, Casey]

> -----Original Message-----
> From: Jiri Kosina [mailto:jikos@xxxxxxxxxx]
> 
> 

> @@ -325,10 +326,13 @@ static int __ptrace_may_access(struct task_struct
> *task, unsigned int mode)
>  	mm = task->mm;
>  	if (mm &&
>  	    ((get_dumpable(mm) != SUID_DUMP_USER) &&
> -	     !ptrace_has_cap(mm->user_ns, mode)))
> +	     ((mode & PTRACE_MODE_NOACCESS_CHK) ||
> +	       !ptrace_has_cap(mm->user_ns, mode))))
>  	    return -EPERM;
> 
> -	return security_ptrace_access_check(task, mode);
> +	if (!(mode & PTRACE_MODE_NOACCESS_CHK))
> +		return security_ptrace_access_check(task, mode);
> +	return 0;

Because PTRACE_MODE_IBPB includes PTRACE_MODE_NOAUDIT you
shouldn't need this change. Do you have a good way to exercise this code
path? I'm having trouble getting to the check, and have yet to get a case
where PTRACE_MODE_NOACCESS_CHK is set.

>  }
> 
>  bool ptrace_may_access(struct task_struct *task, unsigned int mode)
> 
> --
> Jiri Kosina
> SUSE Labs