On 7 October 2015 at 18:56, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> On 7 October 2015 at 17:02, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>> On 7 October 2015 at 16:49, Mark Salter <msalter@xxxxxxxxxx> wrote:
>>> On Wed, 2015-10-07 at 09:35 +0100, Ard Biesheuvel wrote:
>>>> This fixes two issues with the EFI libstub code that removes the memory
>>>> nodes from the FDT:
>>>> a) fdt_del_node() invalidates the iterator, so we should restart from the
>>>> top after calling it;
>>>> b) use fixed length of 6 when matching against 'memory' using strncmp(),
>>>> since otherwise, substrings like 'm' or 'mem' could match as well.
>>>>
>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>>>> ---
>>>> drivers/firmware/efi/libstub/fdt.c | 5 +++--
>>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
>>>> index 0ef16923b4f0..2c7d09936479 100644
>>>> --- a/drivers/firmware/efi/libstub/fdt.c
>>>> +++ b/drivers/firmware/efi/libstub/fdt.c
>>>> @@ -200,6 +200,7 @@ efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
>>>> * Delete any memory nodes present. We must delete nodes which
>>>> * early_init_dt_scan_memory may try to use.
>>>> */
>>>> +restart:
>>>> prev = 0;
>>>> for (;;) {
>>>> const char *type;
>>>> @@ -210,9 +211,9 @@ efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
>>>> break;
>>>>
>>>> type = fdt_getprop(fdt, node, "device_type", &len);
>>>> - if (type && strncmp(type, "memory", len) == 0) {
>>>> + if (type && strncmp(type, "memory", 6) == 0) {
>>>
>>> I see what you're trying to fix here, but I think using 6 is wrong
>>> also. A plain strcmp() would work as long as property is a string.
>>>
>>
>> That is what Leif suggested as well, but it pulls in yet another
>> string function into the stub, so I tried to avoid it. I think this
>> particular case is safe, since the property names are in the string
>> table, which is after the nodes in the DTB structure, so 'type' is
>> guaranteed not to point right before the end of a mapped region.
>>
>
> ... or is your concern about matching on longer strings that only
> start with 'memory'?
>
> I guess it makes sense to use strcmp() after all, only arm64 does not
> have an asm implementation, so under the stricter rules that I am
> proposing for fencing off the EFI stub code from the kernel proper, I
> will have to go and add a strcmp() implementation to
> drivers/firmware/efi/libstub/string.c.
>
OK, strike that. It does have an asm implementation, I just have to
expose it to the stub,
Thanks,
Ard.
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