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?
>
> 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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