Re: [Xen-devel] [PATCH 1/2] xen/livepatch: Clean up arch relocation handling

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.06.17 at 15:44, <konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Jun 13, 2017 at 09:51:35PM +0100, Andrew Cooper wrote:
>> --- a/xen/arch/arm/arm32/livepatch.c
>> +++ b/xen/arch/arm/arm32/livepatch.c
>> @@ -224,21 +224,21 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
>>                             const struct livepatch_elf_sec *rela,
>>                             bool use_rela)
>>  {
>> -    const Elf_RelA *r_a;
>> -    const Elf_Rel *r;
>> -    unsigned int symndx, i;
>> -    uint32_t val;
>> -    void *dest;
>> +    unsigned int i;
>>      int rc = 0;
>>  
>>      for ( i = 0; i < (rela->sec->sh_size / rela->sec->sh_entsize); i++ )
>>      {
>> +        unsigned int symndx;
>> +        uint32_t val;
>> +        void *dest;
>>          unsigned char type;
>> -        s32 addend = 0;
>> +        s32 addend;
>>  
>>          if ( use_rela )
>>          {
>> -            r_a = rela->data + i * rela->sec->sh_entsize;
>> +            const Elf_RelA *r_a = rela->data + i * rela->sec->sh_entsize;
>> +
>>              symndx = ELF32_R_SYM(r_a->r_info);
>>              type = ELF32_R_TYPE(r_a->r_info);
>>              dest = base->load_addr + r_a->r_offset; /* P */
>> @@ -246,10 +246,12 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
>>          }
>>          else
>>          {
>> -            r = rela->data + i * rela->sec->sh_entsize;
>> +            const Elf_Rel *r = rela->data + i * rela->sec->sh_entsize;
>> +
>>              symndx = ELF32_R_SYM(r->r_info);
>>              type = ELF32_R_TYPE(r->r_info);
>>              dest = base->load_addr + r->r_offset; /* P */
>> +            addend = get_addend(type, dest);
>>          }
>>  
>>          if ( symndx > elf->nsym )
>> @@ -259,13 +261,11 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
>>              return -EINVAL;
>>          }
>>  
>> -        if ( !use_rela )
>> -            addend = get_addend(type, dest);
> 
> This was added right after the symndx > elf->nsym check as
> way to make sure we won't dereference the dest (b/c the symbol
> may be outside the bounds).

But symndx isn't being used here.

Jan


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