Re: [Xen-devel] [PATCH v4 07/16] livepatch/arm/x86: Check payload for for unwelcomed symbols.

[Julien Grall <julien.grall@xxxxxxx>]

On 19/09/2016 16:11, Jan Beulich wrote:
> > > > On 19.09.16 at 15:33, <julien.grall@xxxxxxx> wrote:
> > On 19/09/2016 11:27, Jan Beulich wrote:
> > > > > > On 16.09.16 at 18:38, <konrad.wilk@xxxxxxxxxx> wrote:
> > > > --- a/xen/arch/arm/livepatch.c
> > > > +++ b/xen/arch/arm/livepatch.c
> > > > @@ -117,6 +117,20 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf
> > *elf,
> > > >      return true;
> > > >  }
> > > >
> > > > +bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
> > > > +                                const struct livepatch_elf_sym *sym)
> > > > +{
> > > > +#ifdef CONFIG_ARM_32
> > > > +    /*
> > > > +     * Xen does not use Thumb instructions - and we should not see any of
> > > > +     * them. If we do, abort.
> > > > +     */
> > > > +    if ( sym->name && *sym->name == '$' && sym->name[1] == 't' )
> > Please use sym->name[0] for readability. Also, you may want to check the
> > length of the symbol before checking the second character.
> Why would the length check be needed? If the first character is $,
> then looking at the second one is always valid (and it being nul will
> be properly dealt with by the expression above).
Because you may have a payload which is not valid? Or maybe you consider 
that all the payload are trusted.
Regards,

--
Julien Grall

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