Re: [PATCH v2 2/2] livepatch: refuse to resolve symbols that belong to init sections

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Apr 19, 2024 at 12:15:19PM +0200, Jan Beulich wrote:
> On 19.04.2024 12:02, Roger Pau Monne wrote:
> > Livepatch payloads containing symbols that belong to init sections can only
> > lead to page faults later on, as by the time the livepatch is loaded init
> > sections have already been freed.
> > 
> > Refuse to resolve such symbols and return an error instead.
> > 
> > Note such resolutions are only relevant for symbols that point to undefined
> > sections (SHN_UNDEF), as that implies the symbol is not in the current 
> > payload
> > and hence must either be a Xen or a different livepatch payload symbol.
> > 
> > Do not allow to resolve symbols that point to __init_begin, as that address 
> > is
> > also unmapped.  On the other hand, __init_end is not unmapped, and hence 
> > allow
> > resolutions against it.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > Changes since v1:
> >  - Fix off-by-one in range checking.
> 
> Which means you addressed Andrew's comment while at the same time extending
> the scope of ...
> 
> > @@ -310,6 +311,21 @@ int livepatch_elf_resolve_symbols(struct livepatch_elf 
> > *elf)
> >                      break;
> >                  }
> >              }
> > +
> > +            /*
> > +             * Ensure not an init symbol.  Only applicable to Xen symbols, 
> > as
> > +             * livepatch payloads don't have init sections or equivalent.
> > +             */
> > +            else if ( st_value >= (uintptr_t)&__init_begin &&
> > +                      st_value < (uintptr_t)&__init_end )
> > +            {
> > +                printk(XENLOG_ERR LIVEPATCH
> > +                       "%s: symbol %s is in init section, not resolving\n",
> > +                       elf->name, elf->sym[i].name);
> 
> ... what I raised concern about (and I had not seen any verbal reply to that,
> I don't think).

I've extended the commit message to explicitly mention the handling of
bounds for __init_{begin,end} checks.  Let me know if you are not fine
with it (or maybe you expected something else?).

Thanks, Roger.