[PATCH 2/4] efi_loader: check alignment in efi_add_memory_map()

[Heinrich Schuchardt]

On 5/14/20 8:50 PM, Michael Walle wrote:
> Am 2020-05-14 20:35, schrieb Heinrich Schuchardt:
>> On 5/14/20 2:38 PM, Michael Walle wrote:
>>> The first argument has to be aligned with EFI_PAGE_SIZE. This alignment
>>> is already checked for external callers but it is not checked for
>>> internal callers. Unfortunately, most of the time the return value is
>>> not checked, so scream loud and clear.
>>
>> Why do you mention the return value here?
>
> most callers just ignore the return value. so if not aligned this will
> silently fail.
>
>>>
>>> Signed-off-by: Michael Walle <michael at walle.cc>
>>> ---
>>>  lib/efi_loader/efi_memory.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
>>> index fd79178da9..b56e19cb30 100644
>>> --- a/lib/efi_loader/efi_memory.c
>>> +++ b/lib/efi_loader/efi_memory.c
>>> @@ -248,6 +248,9 @@ efi_status_t efi_add_memory_map(uint64_t start,
>>> uint64_t pages, int memory_type,
>>>      EFI_PRINT("%s: 0x%llx 0x%llx %d %s\n", __func__,
>>>            start, pages, memory_type, overlap_only_ram ? "yes" : "no");
>>>
>>> +    if (start & EFI_PAGE_MASK)
>>> +        panic("%s: start not aligned\n", __func__);
>>> +
>>
>> Did you find any internal caller that has a problem?
> See next patch.
>
>> We do not want to increase code size.
> Mh, even within the efi_loader? Well I could do a
>
> if (start & EFI_PAGE_MASK) {
>     debug("%s: start not aligned\n", __func__);
>     return EFI_INVALID_PARAMETER;
> }
>
> but as I said, nobody checks the return value.

The Linux kernel has this nice code comment:
"Don't use BUG() or BUG_ON() unless there's really no way out;"

Looking at the different internal callers, some of these actively ensure
alignment others don't. Wouldn't it make more sense to move all rounding
into a common function taking a start address and a size in bytes as
arguments.

Best regards

Heinrich

>
>