Re: [PATCH] hw/elf_ops: clear uninitialized segment space

[Laurent Vivier]

Le 14/04/2021 à 14:16, Philippe Mathieu-Daudé a écrit :
> On 4/14/21 12:58 PM, Laurent Vivier wrote:
>> When the mem_size of the segment is bigger than the file_size,
>> and if this space doesn't overlap another segment, it needs
>> to be cleared.
>>
>> This bug is very similar to the one we had for linux-user,
>> 22d113b52f41 ("linux-user: Fix loading of BSS segments"),
>> where .bss section is encoded as an extension of the the data
>> one by setting the segment p_memsz > p_filesz.
>>
>> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
>> ---
>>  include/hw/elf_ops.h | 17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/include/hw/elf_ops.h b/include/hw/elf_ops.h
>> index 6ee458e7bc3c..e3dcee3ee349 100644
>> --- a/include/hw/elf_ops.h
>> +++ b/include/hw/elf_ops.h
>> @@ -562,6 +562,23 @@ static int glue(load_elf, SZ)(const char *name, int fd,
>>                      if (res != MEMTX_OK) {
>>                          goto fail;
>>                      }
>> +                    /*
>> +                     * We need to zero'ify the space that is not copied
>> +                     * from file
>> +                     */
>> +                    if (file_size < mem_size) {
>> +                        static uint8_t zero[4096];
> 
> Given it is unlikely, maybe better use:
> 
>               g_autofree uint8_t *zero = g_new0(uint8_t, 4096);
> 
>

I don't know what is the best solution but this seems to introduce a lot of 
complexity only to have
a page of 0s.

Thanks,
Laurent