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Message-ID: <54c30b02-c19e-4e51-8faf-7d6c5560ef6f@bytedance.com>
Date: Wed, 12 Feb 2025 16:28:46 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: David Hildenbrand <david@...hat.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 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?
>
> Then the comparison below also becomes easier to read.
>
>> /*
>> * If we have any shared mappings that are in the same mm
>> @@ -141,6 +141,14 @@ make_coherent(struct address_space *mapping,
>> struct vm_area_struct *vma,
>> */
>> flush_dcache_mmap_lock(mapping);
>> vma_interval_tree_foreach(mpnt, &mapping->i_mmap, pgoff, pgoff) {
>> + unsigned long mpnt_addr;
>> + /*
>> + * If we are using split PTE locks, then we need to take the pte
>> + * lock. Otherwise we are using shared mm->page_table_lock which
>> + * is already locked, thus cannot take it.
>> + */
>> + bool need_lock = IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS);
>
> Nit: move "unsigned long mpnt_addr;" below this longer variable+init.
OK, will do.
>
>> +
>> /*
>> * 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. */
Thanks,
Qi
>
> ?
>
>> + */
>> + if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE)
>> + need_lock = false;
>
>
>
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