Re: [PATCH v2] mm/alloc_tag: fix vm_module_tags_populate's KASAN poisoning logic

[Suren Baghdasaryan]

On Wed, Dec 4, 2024 at 7:08 AM Hao Ge <hao.ge@xxxxxxxxx> wrote:
>
> Hi Suren
>
>
> Thank you for your review.
>
>
> On 12/4/24 22:39, Suren Baghdasaryan wrote:
> > On Wed, Dec 4, 2024 at 12:35 AM Hao Ge <hao.ge@xxxxxxxxx> wrote:
> >> From: Hao Ge <gehao@xxxxxxxxxx>
> >>
> >> After merge commit 233e89322cbe ("alloc_tag:
> >> fix module allocation tags populated area calculation"),
> >> We still encountered a KASAN bug.
> >>
> >> This is because we have only actually performed
> >> page allocation and address mapping here.
> >> we need to unpoisoned portions of underlying memory.
> >>
> >> Because we have a change in the size here,we need to
> >> re-annotate poisoned and unpoisoned portions of underlying memory
> >> according to the new size.
> >>
> >> Here is the log for KASAN:
> >>
> >> [    5.041171][    T1] ==================================================================
> >> [    5.042047][    T1] BUG: KASAN: vmalloc-out-of-bounds in move_module+0x2c0/0x708
> >> [    5.042723][    T1] Write of size 240 at addr ffff80007e510000 by task systemd/1
> >> [    5.043412][    T1]
> >> [    5.043523][   T72] input: QEMU QEMU USB Tablet as /devices/pci0000:00/0000:00:01.1/0000:02:001
> >> [    5.043614][    T1] CPU: 0 UID: 0 PID: 1 Comm: systemd Not tainted 6.13.0-rc1+ #28
> >> [    5.045560][    T1] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> >> [    5.046328][    T1] Call trace:
> >> [    5.046670][    T1]  show_stack+0x20/0x38 (C)
> >> [    5.047127][    T1]  dump_stack_lvl+0x80/0xf8
> >> [    5.047533][    T1]  print_address_description.constprop.0+0x58/0x358
> >> [    5.048092][   T72] hid-generic 0003:0627:0001.0001: input,hidraw0: USB HID v0.01 Mouse [QEMU 0
> >> [    5.048126][    T1]  print_report+0xb0/0x280
> >> [    5.049682][    T1]  kasan_report+0xb8/0x108
> >> [    5.050170][    T1]  kasan_check_range+0xe8/0x190
> >> [    5.050685][    T1]  memcpy+0x58/0xa0
> >> [    5.051135][    T1]  move_module+0x2c0/0x708
> >> [    5.051586][    T1]  layout_and_allocate.constprop.0+0x308/0x5b8
> >> [    5.052219][    T1]  load_module+0x134/0x16c8
> >> [    5.052671][    T1]  init_module_from_file+0xdc/0x138
> >> [    5.053193][    T1]  idempotent_init_module+0x344/0x600
> >> [    5.053742][    T1]  __arm64_sys_finit_module+0xbc/0x150
> >> [    5.054289][    T1]  invoke_syscall+0xd4/0x258
> >> [    5.054749][    T1]  el0_svc_common.constprop.0+0xb4/0x240
> >> [    5.055319][    T1]  do_el0_svc+0x48/0x68
> >> [    5.055743][    T1]  el0_svc+0x40/0xe0
> >> [    5.056142][    T1]  el0t_64_sync_handler+0x10c/0x138
> >> [    5.056658][    T1]  el0t_64_sync+0x1ac/0x1b0
> >>
> >> Fixes: 233e89322cbe ("alloc_tag: fix module allocation tags populated area calculation")
> >> Signed-off-by: Hao Ge <gehao@xxxxxxxxxx>
> > Thanks for the fix!
> >
> >> ---
> >> v2: Add comments to kasan_unpoison_vmalloc like other places.
> >>
> >> commit 233e89322cbe ("alloc_tag: fix module allocation
> >> tags populated area calculation") is currently in the
> >> mm-hotfixes-unstable branch, so this patch is
> >> developed based on the mm-hotfixes-unstable branch.
> >> ---
> >>   lib/alloc_tag.c | 13 +++++++++++++
> >>   1 file changed, 13 insertions(+)
> >>
> >> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> >> index 4ee6caa6d2da..f885b3f3af0e 100644
> >> --- a/lib/alloc_tag.c
> >> +++ b/lib/alloc_tag.c
> >> @@ -421,7 +421,20 @@ static int vm_module_tags_populate(void)
> >>                                  __free_page(next_page[i]);
> >>                          return -ENOMEM;
> >>                  }
> >> +
> >> +               kasan_poison_vmalloc((void *)module_tags.start_addr,
> >> +                                    vm_module_tags->nr_pages << PAGE_SHIFT);
> >> +
> >>                  vm_module_tags->nr_pages += nr;
> >> +
> >> +               /*
> >> +                * Mark the pages as accessible, now that they are mapped.
> >> +                * With hardware tag-based KASAN, marking is skipped for
> >> +                * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
> >> +                */
> >> +               kasan_unpoison_vmalloc((void *)module_tags.start_addr,
> >> +                                      vm_module_tags->nr_pages << PAGE_SHIFT,
> >> +                                      KASAN_VMALLOC_PROT_NORMAL);
> > Instead of poisoning [module_tags.start_addr,
> > vm_module_tags->nr_pages], incrementing vm_module_tags->nr_pages and
> > the unpoisoning [module_tags.start_addr, vm_module_tags->nr_pages]
> > could we simply poisons the additional area like this:
> >
> >                  kasan_unpoison_vmalloc((void *)module_tags.start_addr +
> >                                         (vm_module_tags->nr_pages << PAGE_SHIFT),
> >                                         nr << PAGE_SHIFT,
> >                                         KASAN_VMALLOC_PROT_NORMAL);
> >                 vm_module_tags->nr_pages += nr;
> > ?
>
>
> I had considered making such modifications earlier.
>
> But considering the following situation,
>
> A module tags spans across the regions of [module_tags.start_addr,
> vm_module_tags->nr_pages] and [module_tags.start_addr +
> vm_module_tags->nr_pages, ...].
>
> It may result in false positives for out-of-bounds errors.

Sorry, maybe I'm missing something but I don't see why poisoning only
newly mapped area would lead to false positives. Could you please
clarify?

Also, if you do need to unpoison and then poison, using phys_end and
new_end would be better, like this:

kasan_poison_vmalloc((void *)module_tags.start_addr,
                                      phys_end - module_tags.start_addr)

kasan_unpoison_vmalloc((void *)module_tags.start_addr,
                                          new_end - module_tags.start_addr,
                                          KASAN_VMALLOC_PROT_NORMAL);

>
>
> >>          }
> >>
> >>          return 0;
> >> --
> >> 2.25.1
> >>