Re: [Xen-devel] [PATCH v5 2/4] livepatch: Add limit of 2MB to payload .bss sections.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.16 at 17:48, <konrad.wilk@xxxxxxxxxx> wrote:
> The initial patch: 11ff40fa7bb5fdcc69a58d0fec49c904ffca4793
> "xen/xsplice: Hypervisor implementation of XEN_XSPLICE_op" caps the
> size of the binary at 2MB. We follow that in capping the size
> of the .BSSes to be at maximum 2MB.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> ---
> Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> 
> v5: Initial submission. Came about from conversation about
>     "livepatch: Clear .bss when payload is reverted"
>    - Use only one sh_flags comparison instead of two.
>    - And check for the _right_ combination (WA).
> ---
>  xen/common/livepatch_elf.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
> index cda9b27..e2264ad 100644
> --- a/xen/common/livepatch_elf.c
> +++ b/xen/common/livepatch_elf.c
> @@ -86,7 +86,15 @@ static int elf_resolve_sections(struct livepatch_elf *elf, 
> const void *data)
>                      delta < sizeof(Elf_Ehdr) ? "at ELF header" : "is past 
> end");
>              return -EINVAL;
>          }
> -

I think this blank line would better be retained (after the addition you
make).

> +        else if ( (sec[i].sec->sh_flags & (SHF_WRITE | SHF_ALLOC)) &&
> +                  sec[i].sec->sh_type == SHT_NOBITS &&
> +                  sec[i].sec->sh_size > MB(2) )
> +        {
> +            /* Arbitrary limit. */

I guess this is as arbitrary as the one in verify_payload(). I'd like to
recommend making this a #define, with the comment put next to it.

> +            dprintk(XENLOG_ERR, LIVEPATCH "%s: Section [%u] .bss is bigger 
> than 2MB!\n",
> +                    elf->name, i);

The other limit violation doesn't get a message logged.

Jan


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