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Message-ID: <1399ea09-b53c-4eba-a023-34b8906c9bdd@redhat.com>
Date: Wed, 12 Feb 2025 09:30:20 +0100
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: linux@...linux.org.uk, ezra@...yb.ch, hughd@...gle.com,
ryan.roberts@....com, akpm@...ux-foundation.org, muchun.song@...ux.dev,
linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] arm: pgtable: fix NULL pointer dereference issue
On 12.02.25 09:28, Qi Zheng wrote:
>
>
> On 2025/2/12 16:20, David Hildenbrand wrote:
>> On 12.02.25 07:40, Qi Zheng wrote:
>>> When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
>>> parameter is NULL, which will cause a NULL pointer dereference issue in
>>> adjust_pte():
>>>
>>> Unable to handle kernel NULL pointer dereference at virtual address
>>> 00000030 when read
>>> Hardware name: Atmel AT91SAM9
>>> PC is at update_mmu_cache_range+0x1e0/0x278
>>> LR is at pte_offset_map_rw_nolock+0x18/0x2c
>>> Call trace:
>>> update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
>>> remove_migration_pte from rmap_walk_file+0xcc/0x130
>>> rmap_walk_file from remove_migration_ptes+0x90/0xa4
>>> remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
>>> migrate_pages_batch from migrate_pages+0x188/0x488
>>> migrate_pages from compact_zone+0x56c/0x954
>>> compact_zone from compact_node+0x90/0xf0
>>> compact_node from kcompactd+0x1d4/0x204
>>> kcompactd from kthread+0x120/0x12c
>>> kthread from ret_from_fork+0x14/0x38
>>> Exception stack(0xc0d8bfb0 to 0xc0d8bff8)
>>>
>>> To fix it, do not rely on whether 'ptl' is equal to decide whether to
>>> hold
>>> the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
>>> enabled. In addition, if two vmas map to the same PTE page, there is no
>>> need to hold the pte lock again, otherwise a deadlock will occur. Just
>>> add
>>> the need_lock parameter to let adjust_pte() know this information.
>>>
>>> Reported-by: Ezra Buehler <ezra@...yb.ch>
>>> Closes:
>>> https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@mail.gmail.com/
>>> Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>>> ---
>>> arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------
>>> 1 file changed, 28 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
>>> index 2bec87c3327d2..3627bf0957c75 100644
>>> --- a/arch/arm/mm/fault-armv.c
>>> +++ b/arch/arm/mm/fault-armv.c
>>> @@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> }
>>> static int adjust_pte(struct vm_area_struct *vma, unsigned long
>>> address,
>>> - unsigned long pfn, struct vm_fault *vmf)
>>> + unsigned long pfn, bool need_lock)
>>> {
>>> spinlock_t *ptl;
>>> pgd_t *pgd;
>>> @@ -99,12 +99,11 @@ static int adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> if (!pte)
>>> return 0;
>>> - /*
>>> - * If we are using split PTE locks, then we need to take the page
>>> - * lock here. Otherwise we are using shared mm->page_table_lock
>>> - * which is already locked, thus cannot take it.
>>> - */
>>> - if (ptl != vmf->ptl) {
>>> + if (need_lock) {
>>> + /*
>>> + * Use nested version here to indicate that we are already
>>> + * holding one similar spinlock.
>>> + */
>>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
>>> if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
>>> pte_unmap_unlock(pte, ptl);
>>> @@ -114,7 +113,7 @@ static int adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> ret = do_adjust_pte(vma, address, pfn, pte);
>>> - if (ptl != vmf->ptl)
>>> + if (need_lock)
>>> spin_unlock(ptl);
>>> pte_unmap(pte);
>>> @@ -123,16 +122,17 @@ static int adjust_pte(struct vm_area_struct
>>> *vma, unsigned long address,
>>> static void
>>> make_coherent(struct address_space *mapping, struct vm_area_struct
>>> *vma,
>>> - unsigned long addr, pte_t *ptep, unsigned long pfn,
>>> - struct vm_fault *vmf)
>>> + unsigned long addr, pte_t *ptep, unsigned long pfn)
>>> {
>>> struct mm_struct *mm = vma->vm_mm;
>>> struct vm_area_struct *mpnt;
>>> unsigned long offset;
>>> + unsigned long start;
>>> pgoff_t pgoff;
>>> int aliases = 0;
>>> pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
>>> + start = ALIGN_DOWN(addr, PMD_SIZE);
>>
>> I assume you can come up with a better name than "start" :)
>>
>> aligned_addr ... pmd_start_addr ...
>>
>> Maybe simply
>>
>> pmd_start_addr = ALIGN_DOWN(addr, PMD_SIZE);
>> pmd_end_addr = addr + PMD_SIZE;
>
> you mean:
>
> pmd_end_addr = pmd_start_addr + PMD_SIZE;
>
> Right?
Yes :)
>>
>>> +
>>> /*
>>> * If this VMA is not in our MM, we can ignore it.
>>> * Note that we intentionally mask out the VMA
>>> @@ -151,7 +159,15 @@ make_coherent(struct address_space *mapping,
>>> struct vm_area_struct *vma,
>>> if (!(mpnt->vm_flags & VM_MAYSHARE))
>>> continue;
>>> offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
>>> - aliases += adjust_pte(mpnt, mpnt->vm_start + offset, pfn, vmf);
>>> + mpnt_addr = mpnt->vm_start + offset;
>>> + /*
>>> + * If mpnt_addr and addr are mapped to the same PTE page, there
>>> + * is no need to hold the pte lock again, otherwise a deadlock
>>> + * will occur.
>>
>> /*
>> * Avoid deadlocks by not grabbing the PTE lock if we already hold the
>> * PTE lock of this PTE table in the caller.
>> */
>
> Maybe just:
>
> /* Avoid deadlocks by not grabbing the same PTE lock again. */
>
Agreed.
--
Cheers,
David / dhildenb
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