On 22/08/2024 17:10, Joey Gouly wrote:
@@ -371,6 +382,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) if (system_supports_tpidr2()) p->thread.tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0);
if (system_supports_poe())p->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
Here we are only reloading POR_EL0's value if the target is a user thread. However, as this series stands, POR_EL0 is also relevant to kthreads, because any uaccess or GUP done from a kthread will also be checked against POR_EL0. This is especially important in cases like the io_uring kthread, which accesses the memory of the user process that spawned it. To prevent such a kthread from inheriting a stale value of POR_EL0, it seems that we should reload POR_EL0's value in all cases (user and kernel thread).
Other approaches could also be considered (e.g. resetting POR_EL0 to unrestricted when creating a kthread), see my reply on v4 [1].
Kevin
[1] https://lore.kernel.org/linux-arm-kernel/b4f8b351-4c83-43b4-bfbe-8f67f3f56fb...