On Fri, Sep 6, 2013 at 1:24 PM, David Herrmann <[email protected]> wrote: > Hi > > On Fri, Sep 6, 2013 at 12:59 PM, Geert Uytterhoeven > <[email protected]> wrote: >> On Fri, Sep 6, 2013 at 11:55 AM, David Herrmann <[email protected]> >> wrote: >>> On Fri, Sep 6, 2013 at 11:32 AM, Tom Gundersen <[email protected]> wrote: >>>> lfb_size can easily be say 4M, which would make the bitshit overflow and >>>> the test fail. >>>> >>>> Signed-off-by: Tom Gundersen <[email protected]> >>>> Cc: David Herrmann <[email protected]> >>>> Cc: H. Peter Anvin <[email protected]> >>>> --- >>>> arch/x86/kernel/sysfb_simplefb.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kernel/sysfb_simplefb.c >>>> b/arch/x86/kernel/sysfb_simplefb.c >>>> index 22513e9..fff44a5 100644 >>>> --- a/arch/x86/kernel/sysfb_simplefb.c >>>> +++ b/arch/x86/kernel/sysfb_simplefb.c >>>> @@ -72,7 +72,7 @@ __init int create_simplefb(const struct screen_info *si, >>>> * the part that is occupied by the framebuffer */ >>>> len = mode->height * mode->stride; >>>> len = PAGE_ALIGN(len); >>>> - if (len > si->lfb_size << 16) { >>>> + if (len > ((unsigned long) si->lfb_size) << 16) { >> >> On 32-bit, "unsigned long" is the same size as __u32, so this doesn't >> make any difference. > > lfb_size cannot be 4M on 32bit machines. Well, if it is, the firmware > passed bogus information as you cannot have a 262G-region on 32bit. > But on 64bit it can pass 4M just fine. > So we don't care for the 32bit case here, only 64bit. The (__u64) cast > would be more obvious. Don't know.. It's just a sanity check, anyways, > so I'm fine with it.
I used unsigned long simply to match the type of len... >>> Nice catch. vesafb uses "lfb_size * 65535" which causes an implicit >>> cast. I thought <<16 looks nicer but that doesn't do any implicit >>> cast.. >> >> "lfb_size * 65535" is the same. "lfb_size" is __u32, "65535" is int. >> So there's no implicit cast. Or am I missing something? > > Yepp, indeed. My bad, so vesafb doesn't do any better here. > > I wonder, though, which firmware passes such values. It means the > lfb_size area is reserved >4G. We do have huge VMEM these days.. > Tom, on what hardware did you hit that? As always when weird things happen: DMI: Apple Inc. MacBookAir5,1/Mac-66F35F19FE2A0D05, BIOS MBA51.88Z.00EF.B01.1207271122 07/27/2012 Cheers, Tom -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
