Re: [PATCH] arm: pgtable: fix NULL pointer dereference issue

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@easyb.ch Closes: https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cL... Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()") Cc: stable@vger.kernel.org Signed-off-by: Qi Zheng zhengqi.arch@bytedance.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;

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.

• /*
  • 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. */

?

•  */
  

• if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE)
  

• 	need_lock = false;