On Thu, 8 Sep 2022 14:49:09 +0200 Tijl Coosemans <[email protected]> wrote:
> On Wed, 7 Sep 2022 23:18:32 +0300 Konstantin Belousov
> <[email protected]> wrote:
> > On Wed, Sep 07, 2022 at 06:38:04PM +0200, Tijl Coosemans wrote:
> >> So interrupts must have been reenabled somehow, probably by the page
> >> fault handler, and this allows context switches and then another process
> >> can call copyout or copyin and corrupt the trampoline stack and
> >> copyout_buf.
> > I do not see where the interrupts could be reenabled in copyout_fast path,
> > without or with page fault on the userspace access.
>
> The problem is not with userspace page faults. Those are treated
> specially by the page fault handler in exception.s causing copyout_fast
> and copyin_fast to return immediately with EFAULT so copyout and copyin
> fall back to doing a slow copy.
>
> The problem is with page faults on the kernel space accesses. Before
> this commit they were also treated specially, and now they are not. Now
> the page fault handler in exception.s calls trap() which calls
> trap_pfault() etc.
And trap() contains this:
if (trap_enable_intr(type) && td->td_md.md_spinlock_count == 0 &&
frame->tf_eip != (int)cpu_switch_load_gs)
enable_intr();
Where trap_enable_intr(T_PAGEFLT) returns true and enable_intr() is sti.
