Le 3 nov. 2015 6:46 PM, "Aaron Durbin" <adur...@google.com> a écrit :
>
> On Tue, Nov 3, 2015 at 10:28 AM, Vladimir 'phcoder' Serbinenko
> <phco...@gmail.com> wrote:
> > The code itself looks good but I'd like more details. Reading 0xffffffff
> > shouldn't cause reboot. Why does it?
>
> It's probably implementation defined reading a multi-byte object from
> 4GiB-1. Does it wrap? Blow up the machine? Machine check? Transaction
> never gets terminated?
>
It would be interesting to find out. Since it's P4, it may be related to
PAE but paging is disabled when GRUB is active However it shouldn't hold
this patch. Andrei: go ahead, just please add reference to machine and cpu
in the comment and the fact that we have little idea what's going on.
> >
> > Le 1 nov. 2015 3:53 PM, "Andrei Borzenkov" <arvidj...@gmail.com> a
écrit :
> >>
> >> I was debugging problem reported by user on Dell Dimension 8300 - it
> >> rebooted when doing "ls -l". It turned out, the problem was triggered
by
> >> loading cbfs which probed for header. System has 2GB memory, and
attempt to
> >> read from address 0xffffffff caused instant reboot. 0xffffffff was
returned
> >> by read from non-existing address 0xfffffffc.
> >>
> >> The proof of concept patch below avoids it, but I wonder what the
proper
> >> fix is.
> >>
> >> diff --git a/grub-core/fs/cbfs.c b/grub-core/fs/cbfs.c
> >> index a34eb88..a5a2fde 100644
> >> --- a/grub-core/fs/cbfs.c
> >> +++ b/grub-core/fs/cbfs.c
> >> @@ -344,8 +344,9 @@ init_cbfsdisk (void)
> >>
> >> ptr = *(grub_uint32_t *) 0xfffffffc;
> >> head = (struct cbfs_header *) (grub_addr_t) ptr;
> >> + grub_dprintf ("cbfs", "head=%p\n", head);
> >>
> >> - if (!validate_head (head))
> >> + if (0xffffffff - ptr < sizeof (*head) || !validate_head (head))
> >> return;
> >>
> >> cbfsdisk_size = ALIGN_UP (grub_be_to_cpu32 (head->romsize),
> >>
> >>
> >> _______________________________________________
> >> Grub-devel mailing list
> >> Grub-devel@gnu.org
> >> https://lists.gnu.org/mailman/listinfo/grub-devel
> >
> >
> > --
> > coreboot mailing list: coreb...@coreboot.org
> > http://www.coreboot.org/mailman/listinfo/coreboot
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