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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.06.17 at 09:39, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 20/06/2017 08:36, Jan Beulich wrote:
>>>>> On 19.06.17 at 20:18, <konrad.wilk@xxxxxxxxxx> wrote:
>>> On Wed, Jun 14, 2017 at 07:28:39PM +0100, Andrew Cooper wrote:
>>>> Having said that, there is no sanity check that r->r_offset is within
>>>> base->load_addr + sec->sh_size in arm32, whereas both arm64 and x86
>>>> appear to do this check.
>>> True.
>>>
>>> And the tricky part (it was to me at least) was that ARM32 is all
>>> REL and not RELA so the opcode gets modified after the operation.
>>>
>>> Which means it gets a bit complex to add a boundary check in
>>> 'get_addend' .
>>>
>>> Hm, it would seem the best way is to add a
>>>
>>> if ( r->r_offset >= base->sec->sh_size ||                               
>>>     (r->r_offset + sizeof(uint32_t)) > base->sec->sh_size )             
>> Where's the uint32_t coming from here?
> 
> ARM32.  It's a range check that (void *)&disp is within r_offset, as it
> (void *)&disp + sizeof(disp) -1

But not all ARM32 relocations fiddle with a 32-bit word. Granted all
that livepatch code currently supports are, but baking something like
this in makes future modifications more error prone.

Jan


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