Messages in this thread | | | From | Ard Biesheuvel <> | Date | Mon, 11 Mar 2019 17:36:14 +0100 | Subject | Re: [PATCH 2/2] ARM: futex: make futex_detect_cmpxchg more reliable |
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On Mon, 11 Mar 2019 at 17:30, Arnd Bergmann <arnd@arndb.de> wrote: > > On Mon, Mar 11, 2019 at 3:36 PM Ard Biesheuvel > <ard.biesheuvel@linaro.org> wrote: > > On Mon, 11 Mar 2019 at 15:34, Arnd Bergmann <arnd@arndb.de> wrote: > > > On Fri, Mar 8, 2019 at 12:56 PM Ard Biesheuvel > > > <ard.biesheuvel@linaro.org> wrote: > > > > On Fri, 8 Mar 2019 at 11:58, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > > > > On Fri, Mar 08, 2019 at 11:45:21AM +0100, Ard Biesheuvel wrote: > > > > > > My first attempt (before finding the original patch from Mikael Pettersson) > > > was to change the probe to pass '1' as the value instead of '0', that > > > worked fine. > > > > > > > Which probe is that? > > diff --git a/kernel/futex.c b/kernel/futex.c > index c3b73b0311bc..19615ad3c4f7 100644 > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -3864,7 +3864,7 @@ static void __init futex_detect_cmpxchg(void) > * implementation, the non-functional ones will return > * -ENOSYS. > */ > - if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) > + if (cmpxchg_futex_value_locked(&curval, NULL, 1, 1) == -EFAULT) > futex_cmpxchg_enabled = 1; > #endif > } >
Ah ok.
That explains a lot.
Can't we just return -EFAULT if uaddr is NULL? Or does that defeat this check?
Note that PA-RISC has
/* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is * our gateway page, and causes no end of trouble... */ if (uaccess_kernel() && !uaddr) return -EFAULT;
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