On 01/23/2018 06:07 PM, Dominik Brodowski wrote: > On Tue, Jan 23, 2018 at 02:07:01PM +0100, Martin Schwidefsky wrote: >> Add the PR_ISOLATE_BP operation to prctl. The effect of the process >> control is to make all branch prediction entries created by the execution >> of the user space code of this task not applicable to kernel code or the >> code of any other task. > > What is the rationale for requiring a per-process *opt-in* for this added > protection? > > For KPTI on x86, the exact opposite approach is being discussed (see, e.g. > http://lkml.kernel.org/r/1515612500-14505-1-git-send-email-w@xxxxxx ): By > default, play it safe, with KPTI enabled. But for "trusted" processes, one > may opt out using prctrl. FWIW, this is not about KPTI. s390 always has the kernel in a separate address space. Its only about potential spectre like attacks. This idea is to be able to isolate in controlled environments, e.g. if you have only one thread with untrusted code (e.g. jitting remote code). The property of the branch prediction mode on s390 is that it protects in two ways - against being attacked but also against being able to attack via the btb. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
