On Wed, Sep 11, 2024 at 02:08:47PM +0200, Alexey Gladkov wrote:
> On Tue, Sep 10, 2024 at 12:54:19PM -0700, Dave Hansen wrote:
> > On 9/6/24 04:49, Alexey Gladkov wrote:
> > > +static inline bool is_kernel_addr(unsigned long addr)
> > > +{
> > > + return (long)addr < 0;
> > > +}
> > > +
> > > static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
> > > {
> > > unsigned long *reg, val, vaddr;
> > > @@ -434,6 +439,11 @@ static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
> > > return -EINVAL;
> > > }
> > >
> > > + if (!user_mode(regs) && !is_kernel_addr(ve->gla)) {
> > > + WARN_ONCE(1, "Access to userspace address is not supported");
> > > + return -EINVAL;
> > > + }
> >
> > Should we really be open-coding a "is_kernel_addr" check? I mean,
> > TASK_SIZE_MAX is there for a reason. While I doubt we'd ever change the
> > positive vs. negative address space convention on 64-bit, I don't see a
> > good reason to write a 64-bit x86-specific is_kernel_addr() when a more
> > generic, portable and conventional idiom would do.
>
> I took arch/x86/events/perf_event.h:1262 as an example. There is no
> special reason in its own function.
>
> > So, please use either a:
> >
> > addr < TASK_SIZE_MAX
> >
> > check, or use fault_in_kernel_space() directly.
>
> I'll use fault_in_kernel_space() since SEV uses it. Thanks.
Also user_mode() check is redundant until later in the patchset. Move it
to the patch that allows userspace MMIO.
--
Kiryl Shutsemau / Kirill A. Shutemov
