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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.09.16 at 15:33, <julien.grall@xxxxxxx> wrote:
> Hi,
> 
> 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).

Jan


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