Re: [PATCH v11 09/14] kernel, arm64: untag user pointers in prctl_set_mm*

[Andrey Konovalov <andreyknvl@google.com>]

On Mon, Mar 18, 2019 at 12:47 PM Kevin Brodsky <kevin.brodsky@arm.com> wrote:
>
> On 15/03/2019 19:51, Andrey Konovalov wrote:
> > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > pass tagged user pointers (with the top byte set to something else other
> > than 0x00) as syscall arguments.
> >
> > prctl_set_mm() and prctl_set_mm_map() use provided user pointers for vma
> > lookups, which can only by done with untagged pointers.
> >
> > Untag user pointers in these functions.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > ---
> >   kernel/sys.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index 12df0e5434b8..8e56d87cc6db 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -1993,6 +1993,18 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
> >       if (copy_from_user(&prctl_map, addr, sizeof(prctl_map)))
> >               return -EFAULT;
> >
> > +     prctl_map->start_code   = untagged_addr(prctl_map.start_code);
> > +     prctl_map->end_code     = untagged_addr(prctl_map.end_code);
> > +     prctl_map->start_data   = untagged_addr(prctl_map.start_data);
> > +     prctl_map->end_data     = untagged_addr(prctl_map.end_data);
> > +     prctl_map->start_brk    = untagged_addr(prctl_map.start_brk);
> > +     prctl_map->brk          = untagged_addr(prctl_map.brk);
> > +     prctl_map->start_stack  = untagged_addr(prctl_map.start_stack);
> > +     prctl_map->arg_start    = untagged_addr(prctl_map.arg_start);
> > +     prctl_map->arg_end      = untagged_addr(prctl_map.arg_end);
> > +     prctl_map->env_start    = untagged_addr(prctl_map.env_start);
> > +     prctl_map->env_end      = untagged_addr(prctl_map.env_end);
>
> As the buildbot suggests, those -> should be . instead :) You might want to check
> your local build with CONFIG_CHECKPOINT_RESTORE=y.

Oops :)

>
> > +
> >       error = validate_prctl_map(&prctl_map);
> >       if (error)
> >               return error;
> > @@ -2106,6 +2118,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
> >                             opt != PR_SET_MM_MAP_SIZE)))
> >               return -EINVAL;
> >
> > +     addr = untagged_addr(addr);
>
> This is a bit too coarse, addr is indeed used for find_vma() later on, but it is also
> used to access memory, by prctl_set_mm_mmap() and prctl_set_auxv().

Yes, I wrote this patch before our Friday discussion and forgot about
it. I'll fix it in v12, thanks!

>
> Kevin
>
> > +
> >   #ifdef CONFIG_CHECKPOINT_RESTORE
> >       if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
> >               return prctl_set_mm_map(opt, (const void __user *)addr, arg4);
>