Re: [PATCH] mm: fix possible OOB in numa_rebuild_large_mapping()

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

On 2024/6/11 20:32, David Hildenbrand wrote:
> On 07.06.24 12:32, Kefeng Wang wrote:
> > The large folio is mapped with folio size aligned virtual address during
> > the pagefault, eg, 'addr = ALIGN_DOWN(vmf->address, nr_pages * 
> > PAGE_SIZE)'
> > in do_anonymous_page(), but after the mremap(), the virtual address only
> > require PAGE_SIZE aligned, also pte is moved to new in 
> > move_page_tables(),
> > then traverse the new pte in numa_rebuild_large_mapping() will hint the
> > following issue,
> >
> >     Unable to handle kernel paging request at virtual address 
> > 00000a80c021a788
> >     Mem abort info:
> >       ESR = 0x0000000096000004
> >       EC = 0x25: DABT (current EL), IL = 32 bits
> >       SET = 0, FnV = 0
> >       EA = 0, S1PTW = 0
> >       FSC = 0x04: level 0 translation fault
> >     Data abort info:
> >       ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> >       CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> >       GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> >     user pgtable: 4k pages, 48-bit VAs, pgdp=00002040341a6000
> >     [00000a80c021a788] pgd=0000000000000000, p4d=0000000000000000
> >     Internal error: Oops: 0000000096000004 [#1] SMP
> >     ...
> >     CPU: 76 PID: 15187 Comm: git Kdump: loaded Tainted: G        
> > W          6.10.0-rc2+ #209
> >     Hardware name: Huawei TaiShan 2280 V2/BC82AMDD, BIOS 1.79 08/21/2021
> >     pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> >     pc : numa_rebuild_large_mapping+0x338/0x638
> >     lr : numa_rebuild_large_mapping+0x320/0x638
> >     sp : ffff8000b41c3b00
> >     x29: ffff8000b41c3b30 x28: ffff8000812a0000 x27: 00000000000a8000
> >     x26: 00000000000000a8 x25: 0010000000000001 x24: ffff20401c7170f0
> >     x23: 0000ffff33a1e000 x22: 0000ffff33a76000 x21: ffff20400869eca0
> >     x20: 0000ffff33976000 x19: 00000000000000a8 x18: ffffffffffffffff
> >     x17: 0000000000000000 x16: 0000000000000020 x15: ffff8000b41c36a8
> >     x14: 0000000000000000 x13: 205d373831353154 x12: 5b5d333331363732
> >     x11: 000000000011ff78 x10: 000000000011ff10 x9 : ffff800080273f30
> >     x8 : 000000320400869e x7 : c0000000ffffd87f x6 : 00000000001e6ba8
> >     x5 : ffff206f3fb5af88 x4 : 0000000000000000 x3 : 0000000000000000
> >     x2 : 0000000000000000 x1 : fffffdffc0000000 x0 : 00000a80c021a780
> >     Call trace:
> >      numa_rebuild_large_mapping+0x338/0x638
> >      do_numa_page+0x3e4/0x4e0
> >      handle_pte_fault+0x1bc/0x238
> >      __handle_mm_fault+0x20c/0x400
> >      handle_mm_fault+0xa8/0x288
> >      do_page_fault+0x124/0x498
> >      do_translation_fault+0x54/0x80
> >      do_mem_abort+0x4c/0xa8
> >      el0_da+0x40/0x110
> >      el0t_64_sync_handler+0xe4/0x158
> >      el0t_64_sync+0x188/0x190
> >
> > Fix it by correct the start and end, which may lead to only rebuild part
> > of large mapping in one numa page fault, there is no issue since other 
> > part
> > could rebuild by another pagefault.
> >
> > Fixes: d2136d749d76 ("mm: support multi-size THP numa balancing")
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> >   mm/memory.c | 24 +++++++++++++++---------
> >   1 file changed, 15 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index db9130488231..0ad57b6485ca 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5223,15 +5223,21 @@ static void numa_rebuild_single_mapping(struct 
> > vm_fault *vmf, struct vm_area_str
> >       update_mmu_cache_range(vmf, vma, fault_addr, fault_pte, 1);
> >   }
> > -static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct 
> > vm_area_struct *vma,
> > -                       struct folio *folio, pte_t fault_pte,
> > -                       bool ignore_writable, bool pte_write_upgrade)
> > +static void numa_rebuild_large_mapping(struct vm_fault *vmf,
> > +        struct vm_area_struct *vma, struct folio *folio, int nr_pages,
> > +        pte_t fault_pte, bool ignore_writable, bool pte_write_upgrade)
> >   {
> >       int nr = pte_pfn(fault_pte) - folio_pfn(folio);
> > -    unsigned long start = max(vmf->address - nr * PAGE_SIZE, 
> > vma->vm_start);
> > -    unsigned long end = min(vmf->address + (folio_nr_pages(folio) - 
> > nr) * PAGE_SIZE, vma->vm_end);
> > -    pte_t *start_ptep = vmf->pte - (vmf->address - start) / PAGE_SIZE;
> > -    unsigned long addr;
> > +    unsigned long folio_size = nr_pages * PAGE_SIZE;
>
> Just re-read folio_nr_pages() here, it's cheap. Or even better, use 
> folio_size();
>
> > +    unsigned long addr = vmf->address;
> > +    unsigned long start, end, align_addr;
> > +    pte_t *start_ptep;
> > +
> > +    align_addr = ALIGN_DOWN(addr, folio_size);
> > +    start = max3(addr - nr * PAGE_SIZE, align_addr, vma->vm_start);
> > +    end = min3(addr + (nr_pages - nr) * PAGE_SIZE, align_addr + 
> > folio_size,
>
> Please avoid mixing nr_pages and folio_size.
>
> > +           vma->vm_end);
> > +    start_ptep = vmf->pte - (addr - start) / PAGE_SIZE;
>                  writable);
>
> I am not able to convince myself that the old code could not have 
> resulted in a vmf->pte that underflows the page table. Am I correct?

Yes, I think you are right, and I realized the problem now.

> Now align_addr would make sure that we are always within one page table 
> (as long as our folio size does not exceed PMD size :) ).
>
> Can we use PMD_SIZE instead for that, something like the following?
>
>
> /* Stay within the VMA and within the page table. */
> pt_start = ALIGN_DOWN(addr, PMD_SIZE);
> start = max3(addr - nr << PAGE_SHIFT, pt_start, vma->vm_start);
> end = min3(addr + folio_size - nr << PAGE_SHIFT,
>             pt_start + PMD_SIZE, vma->vm_end);
>
> start_ptep = vmf->pte - (addr - start) >> PAGE_SHIFT;

The changes look good to me. Thanks.