On Tue, Apr 23, 2024 at 03:44:42PM +0200, Jan Beulich wrote:
> On 23.04.2024 15:12, 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.
> >
> > Since __init_begin can alias other symbols (like _erodata for example)
> > allow the force flag to override the check and resolve the symbol anyway.
> >
> > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
>
> In principle, as promised (and just to indicate earlier concerns were
> addressed, as this is meaningless for other purposes)
> Acked-by: Jan Beulich <jbeul...@suse.com>
> However, ...
>
> > @@ -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 && !force )
> > + {
> > + printk(XENLOG_ERR LIVEPATCH
> > + "%s: symbol %s is in init section, not resolving\n",
> > + elf->name, elf->sym[i].name);
> > + rc = -ENXIO;
> > + break;
> > + }
>
> ... wouldn't it make sense to still warn in this case when "force" is set?
Pondered it, I was thinking that a user would first run without
--force, and use the option as a result of seeing the first failure.
However if there is more than one check that's bypassed, further ones
won't be noticed, so:
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);
if ( !force )
{
rc = -ENXIO;
break;
}
}
Would be OK then?
Thanks, Roger.
