[PATCH makedumpfile] Avoid false-positive mem_section validation with vmlinux

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Pingfan, Philipp,

Thank you for reviewing and testing this, applied.
https://github.com/makedumpfile/makedumpfile/commit/6d0d95ecc04a70f8448d562ff0fbbae237f5c929

Kazu

-----Original Message-----
> On Thu, Apr 21, 2022 at 7:58 AM HAGIO KAZUHITO(萩尾　一仁)
> <k-hagio-ab at nec.com> wrote:
> >
> > Currently get_mem_section() validates if SYMBOL(mem_section) is the address
> > of the mem_section array first.  But there was a report that the first
> > validation wrongly returned TRUE with -x vmlinux and SPARSEMEM_EXTREME
> > (4.15+) on s390x.  This leads to crash failing statup with the following
> > seek error:
> >
> >   crash: seek error: kernel virtual address: 67fffc2800  type: "memory section root table"
> >
> > Skip the first validation when satisfying the conditions.
> >
> > Reported-by: Dave Wysochanski <dwysocha at redhat.com>
> > Signed-off-by: Kazuhito Hagio <k-hagio-ab at nec.com>
> > ---
> >  makedumpfile.c | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> >
> > diff --git a/makedumpfile.c b/makedumpfile.c
> > index a2f45c84cee3..65d1c7c2f02c 100644
> > --- a/makedumpfile.c
> > +++ b/makedumpfile.c
> > @@ -3698,6 +3698,22 @@ validate_mem_section(unsigned long *mem_sec,
> >         return ret;
> >  }
> >
> > +/*
> > + * SYMBOL(mem_section) varies with the combination of memory model and
> > + * its source:
> > + *
> > + * SPARSEMEM
> > + *   vmcoreinfo: address of mem_section root array
> > + *   -x vmlinux: address of mem_section root array
> > + *
> > + * SPARSEMEM_EXTREME v1
> > + *   vmcoreinfo: address of mem_section root array
> > + *   -x vmlinux: address of mem_section root array
> > + *
> > + * SPARSEMEM_EXTREME v2 (with 83e3c48729d9 and a0b1280368d1) 4.15+
> > + *   vmcoreinfo: address of mem_section root array
> > + *   -x vmlinux: address of pointer to mem_section root array
> > + */
> >  static int
> >  get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
> >                 unsigned int num_section)
> > @@ -3710,12 +3726,27 @@ get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
> >                     strerror(errno));
> >                 return FALSE;
> >         }
> > +
> > +       /*
> > +        * There was a report that the first validation wrongly returned TRUE
> > +        * with -x vmlinux and SPARSEMEM_EXTREME v2 on s390x, so skip it.
> > +        * Howerver, leave the fallback validation as it is for the -i option.
> > +        */
> > +       if (is_sparsemem_extreme() && info->name_vmlinux) {
> > +               unsigned long flag = 0;
> > +               if (get_symbol_type_name("mem_section", DWARF_INFO_GET_SYMBOL_TYPE,
> > +                                       NULL, &flag)
> > +                   && !(flag & TYPE_ARRAY))
> > +                       goto skip_1st_validation;
> > +       }
> > +
> >         ret = validate_mem_section(mem_sec, SYMBOL(mem_section),
> >                                    mem_section_size, mem_maps, num_section);
> >
> >         if (!ret && is_sparsemem_extreme()) {
> >                 unsigned long mem_section_ptr;
> >
> > +skip_1st_validation:
> >                 if (!readmem(VADDR, SYMBOL(mem_section), &mem_section_ptr,
> >                              sizeof(mem_section_ptr)))
> >                         goto out;
> > --
> > 2.27.0
> >
> Discussed with Kazu off-list, and with his nice help, I got clear why
> he drops V1.
> 
> Hence,
> Reviewed-by: Pingfan Liu <piliu at redhat.com>