Re: [Xen-devel] [PATCH v4 1/9] livepatch: Clear .bss when payload is reverted

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Sep 07, 2016 at 02:02:44AM -0600, Jan Beulich wrote:
> >>> On 06.09.16 at 18:47, <konrad.wilk@xxxxxxxxxx> wrote:
> > On Wed, Aug 24, 2016 at 02:55:21AM -0600, Jan Beulich wrote:
> >> >>> On 24.08.16 at 04:22, <konrad.wilk@xxxxxxxxxx> wrote:
> >> > --- a/xen/common/livepatch.c
> >> > +++ b/xen/common/livepatch.c
> >> > @@ -70,6 +70,9 @@ struct payload {
> >> >      unsigned int nsyms;                  /* Nr of entries in .strtab 
> >> > and symbols. */
> >> >      struct livepatch_build_id id;        /* 
> >> > ELFNOTE_DESC(.note.gnu.build-id) of the payload. */
> >> >      struct livepatch_build_id dep;       /* 
> >> > ELFNOTE_DESC(.livepatch.depends). */
> >> > +    void **bss;                          /* .bss's of the payload. */
> >> > +    size_t *bss_size;                    /* and their sizes. */
> >> 
> >> Is size_t wide enough in the extreme case? Perhaps yes, because I
> >> don't think we'll ever load 64-bit ELF on a 32-bit platform.
> > 
> > Nonethless having a huge .bss is a kind of extreme? Perhaps we should
> > have an seperate patch that checks the SHT_NOBITS and disallows .bss's
> > bigger than say 2MB?
> 
> Well, the extra check certainly wouldn't hurt, but I think before
> hitting the size_t limit you'd run out of address space to place
> the payload in (as that's iirc a less than 1Gb area).

True. And on ARM 32|64 even smaller (2MB). Let me force an
even smaller width type - say 'unsigned int'.
> 
> Jan
> 

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