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

[Philippe Mathieu-Daudé]

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);

> +                        uint64_t i;
> +                        for (i = file_size; i < mem_size; i += sizeof(zero)) 
> {
> +                            res = address_space_write(
> +                                         as ? as : &address_space_memory,
> +                                         addr + i, MEMTXATTRS_UNSPECIFIED,
> +                                         zero, MIN(sizeof(zero), mem_size - 
> i));
> +                            if (res != MEMTX_OK) {
> +                                goto fail;
> +                            }
> +                        }
> +                    }
>                  }
>              }
>  
>