On 19/04/2021 17:37, Ralf Ramsauer wrote:
> Hi Bram,
>
> On 19/04/2021 14:17, Bram Hooimeijer wrote:
>> When creating a new page table, the table should be filled with zeroes
>> to prevent decoding invalid entries as valid in the future. Given that
>> in the inmate memory space no assumptions can be made on the contents of
>> unallocated heapspace, zeroing needs to be done explicitly.
>
> Don't we already zero pages when reloading a guest? (I'm not sure)
> IOW: Did you really experience dirty pages?
Just cross-checked: Looks like we don't zero inmate memory on cell
reload. Now I wonder why I never experienced a similar bug… But we
haven't many inmates that make excessive use of the heap.
>
> Anyway, if we don't, then we should think if we should zero them. The
> question is, if it is acceptable to leave artefacts of previously
> running inmates in memory.
I think we should rather implement a zalloc() wrapper around alloc(),
which gives us guarantees to return zeroed pages. We have some other
spots in libinmate where we could substitute alloc/memset-sequences in
libinmate, e.g. in lib/arm-common/mem.c and lib/x86/smp.c.
Ralf
>
> Thanks
> Ralf
>
>>
>> Signed-off-by: Bram Hooimeijer <[email protected]>
>> ---
>> inmates/lib/x86/mem.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/inmates/lib/x86/mem.c b/inmates/lib/x86/mem.c
>> index 7e1c8b83..45424ea1 100644
>> --- a/inmates/lib/x86/mem.c
>> +++ b/inmates/lib/x86/mem.c
>> @@ -58,6 +58,7 @@ void map_range(void *start, unsigned long size, enum
>> map_type map_type)
>> pt = (unsigned long *)(*pt_entry & PAGE_MASK);
>> } else {
>> pt = alloc(PAGE_SIZE, PAGE_SIZE);
>> + memset(pt, 0, PAGE_SIZE);
>> *pt_entry = (unsigned long)pt | PAGE_DEFAULT_FLAGS;
>> }
>>
>> @@ -66,6 +67,7 @@ void map_range(void *start, unsigned long size, enum
>> map_type map_type)
>> pt = (unsigned long *)(*pt_entry & PAGE_MASK);
>> } else {
>> pt = alloc(PAGE_SIZE, PAGE_SIZE);
>> + memset(pt, 0, PAGE_SIZE);
>> *pt_entry = (unsigned long)pt | PAGE_DEFAULT_FLAGS;
>> }
>>
>>
>
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