On Wed, May 25, 2016 at 2:49 AM, Borislav Petkov <[email protected]> wrote: > On Tue, May 24, 2016 at 03:48:42PM -0700, Andy Lutomirski wrote: >> If a uaccess instruction fails due to an8 error other than #PF, >> warn. If the fault is #GP, it most likely indicates access to a >> non-canonical address, which means that an access_ok check is >> missing, and that's bad. If the fault is something else (#UD?), >> then something is very wrong and we should diagnose it rather >> than ignoring it. >> >> Signed-off-by: Andy Lutomirski <[email protected]> >> --- >> arch/x86/mm/extable.c | 13 +++++++++++++ >> 1 file changed, 13 insertions(+) >> >> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c >> index 658292fdee5e..c1933471fce7 100644 >> --- a/arch/x86/mm/extable.c >> +++ b/arch/x86/mm/extable.c >> @@ -29,6 +29,19 @@ EXPORT_SYMBOL(ex_handler_default); >> static bool uaccess_fault_okay(int trapnr, unsigned long error_code, >> unsigned long extra) >> { >> + /* >> + * For uaccess, only page faults should be fixed up. I can't see >> + * any exploit mitigation value in OOPSing on other types of faults, >> + * so just warn and continue if that happens. This means that >> + * uaccess faults to non-canonical addresses will warn. That's okay >> + * -- this will only happen if an access_ok is missing, and we want to >> + * detect that error if it happens. >> + */ >> + if (WARN_ONCE(trapnr != X86_TRAP_PF, >> + "unexpected uaccess trap %d (may indicate a missing >> access_ok on a non-canonical address)\n", >> + trapnr)) > > Perhaps dump also regs->ip and make the warn message more helpful... >
The stack trace will show it, and I'm not convinced that regs->ip by itself will be all that helpful -- depending on what gets inlined, it could just point to __copy_from_user or similar. >> + return true; /* no good reason to OOPS. */ > > You love those side comments, don'tcha? :-) ECO tip #102: avoid silly newlines :-p --Andy
