Re: [PATCH v3 2/4] x86/traps: Print non-canonical address on #GP

[Jann Horn]

On Wed, Nov 20, 2019 at 1:39 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Wed, Nov 20, 2019 at 01:30:58PM +0100, Ingo Molnar wrote:
> > * Jann Horn <jannh@xxxxxxxxxx> wrote:
> >
> > > You mean something like this?
> > >
> > > ========================
> > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> > > index 9b23c4bda243..16a6bdaccb51 100644
> > > --- a/arch/x86/kernel/traps.c
> > > +++ b/arch/x86/kernel/traps.c
> > > @@ -516,32 +516,36 @@ dotraplinkage void do_bounds(struct pt_regs
> > > *regs, long error_code)
> > >   * On 64-bit, if an uncaught #GP occurs while dereferencing a non-canonical
> > >   * address, return that address.
> > >   */
> > > -static unsigned long get_kernel_gp_address(struct pt_regs *regs)
> > > +static bool get_kernel_gp_address(struct pt_regs *regs, unsigned long *addr,
> > > +                                          bool *non_canonical)
> >
> > Yeah, that's pretty much the perfect end result!
>
> Why do we need the bool thing? Can't we rely on the assumption that an
> address of 0 is the error case and use that to determine whether the
> resolving succeeded or not?

True, that'd work, too. I didn't really want to special-case an
integer here - especially one that has the same value as NULL - but I
guess it's fine.