Re: [RFC6 PATCH v6 00/21] ILP32 for ARM64

[Yury Norov]

On Thu, May 12, 2016 at 03:07:35PM +0100, Catalin Marinas wrote:
> On Thu, May 12, 2016 at 04:44:31PM +0300, Yury Norov wrote:
> > On Thu, May 12, 2016 at 02:35:34PM +0100, Catalin Marinas wrote:
> > > On Thu, May 12, 2016 at 03:20:00AM +0300, Yury Norov wrote:
> > > > I debugged preadv02 and pwritev02 failures and found very weird bug.
> > > > Test passes {iovec_base = 0xffffffff, iovec_len = 64} as one element
> > > > of vector, and kernel reports successful read/write.
> > > > 
> > > > There are 2 problems:
> > > > 1. How kernel allows such address to be passed to fs subsystem;
> > > > 2. How fs successes to read/write at non-mapped, and in fact non-user
> > > > address.
> > > > 
> > > > I don't know the answer on 2'nd question, and it might be something
> > > > generic. But I investigated first problem.
> > > > 
> > > > The problem is that compat_rw_copy_check_uvector() uses access_ok() to
> > > > validate user address, and on arm64 it ends up with checking buffer
> > > > end against current_thread_info()->addr_limit.
> > > > 
> > > > current_thread_info()->addr_limit for ilp32, and most probably for
> > > > aarch32 is equal to aarch64 one, and so adress_ok() doesn't fail.
> > > > It happens because on thread creation we call flush_old_exec() to set 
> > > > addr_limit, and completely ignore compat mode there.
> 
> [...]
> 
> > > > --- a/arch/arm64/kernel/binfmt_elf32.c
> > > > +++ b/arch/arm64/kernel/binfmt_elf32.c
> > > > @@ -12,6 +12,7 @@
> > > >  do {						\
> > > >  	clear_thread_flag(TIF_32BIT_AARCH64);	\
> > > >  	set_thread_flag(TIF_32BIT);		\
> > > > +	set_fs(TASK_SIZE_32);			\
> > > >  } while (0)
> > > >  
> > > >  #define COMPAT_ARCH_DLINFO
> > > > diff --git a/arch/arm64/kernel/binfmt_ilp32.c b/arch/arm64/kernel/binfmt_ilp32.c
> > > > index a934fd4..a8599c6 100644
> > > > --- a/arch/arm64/kernel/binfmt_ilp32.c
> > > > +++ b/arch/arm64/kernel/binfmt_ilp32.c
> > > > @@ -59,6 +59,7 @@ static void cputime_to_compat_timeval(const cputime_t cputime,
> > > >  do {									\
> > > >  	set_thread_flag(TIF_32BIT_AARCH64);				\
> > > >  	clear_thread_flag(TIF_32BIT);					\
> > > > +	set_fs(TASK_SIZE_32);						\
> > > >  } while (0)
> > > 
> > > I don't think we need these two. AFAICT, flush_old_exec() takes care of
> > > setting the USER_DS for the new thread.
> > 
> > That's true, but USER_DS depends on personality which is not set yet
> > for new thread, as I wrote above. In fact, I tried correct USER_DS
> > only, and it doesn't work
> 
> Ah, it looks like load_elf_binary() sets the personality after
> flush_old_exec(). Looking at powerpc and x86, they set USER_DS to the
> maximum 64-bit task value, so they should have a similar issue with
> native 32-bit vs compat behaviour.

Hmmm. If so, it means we'd introduce generic fix. It would be removing 
set_fs() from flush_old_exec() and appending it to load_elf_binary()
after SET_PERSONALITY(). But I think it should be agreed with other
arches developers. I've sent standalone patch for aarch64 (you in CC)
so let's move discussion there.

> So what exactly is LTP complaining about? Is different error (like
> EFAULT vs EINVAL) or not getting an error at all.
 
It should be EINVAL, but it succeed. The other problem is that
following fs routines does not complain on wrong address.

> (I need to update my LTP, the preadv tests appeared in December last
> year)
> 

preadv02 was extended with this testcase in April.

> -- 
> Catalin