Re: [PATCH v3 51/51] x86/mm: convert arch_within_stack_frames() to use the new unwinder

[Kees Cook]

On Fri, Aug 12, 2016 at 8:17 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> On Fri, Aug 12, 2016 at 09:29:10AM -0500, Josh Poimboeuf wrote:
>> Convert arch_within_stack_frames() to use the new unwinder.
>>
>> Boot tested with CONFIG_HARDENED_USERCOPY.
>>
>> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>> ---
>>  arch/x86/lib/usercopy.c | 25 +++++++++++++++++++------
>>  1 file changed, 19 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
>> index 96ce151..9d0913c 100644
>> --- a/arch/x86/lib/usercopy.c
>> +++ b/arch/x86/lib/usercopy.c
>> @@ -50,12 +50,21 @@ int arch_within_stack_frames(const void * const stack,
>>                            const void * const stackend,
>>                            const void *obj, unsigned long len)
>>  {
>> -     const void *frame = NULL;
>> -     const void *oldframe;
>> +     struct unwind_state state;
>> +     const void *frame, *oldframe;
>> +
>> +     unwind_start(&state, current, NULL, NULL);
>> +
>> +     if (!unwind_next_frame(&state))
>> +             return 0;
>> +
>> +     oldframe = unwind_get_stack_ptr(&state);
>
> Actually, I think this isn't quite right.  Now that the function isn't
> inlined, this needs to unwind another frame to be equivalent to current
> behavior.

Yeah, that seems right. And IIUC, as long as this is wrapped in the
CONFIG_FRAME_POINTER check, this won't use the guessing unwinder,
right? (Which is how it should be.)

-Kees

-- 
Kees Cook
Nexus Security