On Fri, Oct 04, 2019 at 08:14:25AM -0700, Dave Hansen wrote:
> On 10/4/19 7:59 AM, Andy Lutomirski wrote:
> >> @@ -123,7 +125,8 @@ __visible bool ex_handler_uaccess(const struct
> >> exception_table_entry *fixup,
> >> unsigned long error_code,
> >> unsigned long fault_addr)
> >> {
> >> - WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user
> >> access. Non-canonical address?");
> >> + WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault at %s
> >> address in user access.",
> >> + is_canonical_addr(fault_addr) ? "canonical" :
> >> "non-canonical");
> > Unless the hardware behaves rather differently from the way I think it
> > does, fault_addr is garbage for anything other than #PF and sometimes
> > for #DF. (And maybe the virtualization faults?) I don't believe that
> > #GP fills in CR2.
>
> For #GP, we do:
>
> do_general_protection(struct pt_regs *regs, long error_code)
> {
> ...
> if (!user_mode(regs)) {
> if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
> return;
>
> Where the 0 is 'fault_addr'. I'm not sure any other way that
> ex_handler_uaccess() can get called with trapnr == X86_TRAP_GP. 0 is
> canonical last I checked, which would make this patch a bit academic. :)
My fault. I thought the 'fault_addr' is filled with a valid value. So we really
don't know the answer without decoding the instruction which causes this #GP. :)
--
Cheers,
Changbin Du
