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Re: [PATCH] hw/elf_ops: clear uninitialized segment space
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH] hw/elf_ops: clear uninitialized segment space |
Date: |
Thu, 15 Apr 2021 10:44:23 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 |
On 4/14/21 2:41 PM, Laurent Vivier wrote:
> 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.
Less complex alternative is to use dma_memory_set():
dma_memory_set(as, file_size, 0, mem_size - file_size);
Actually we should extract address_space_set() from it, keeping
the dma_barrier() call in dma_memory_set(), and use address_space_set()
here.
What do you think?
Phil.