[PATCH v2] arm: pgtable: fix NULL pointer dereference issue - Linux-stable-mirror

14 Feb 2025

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.buehler@husqvarnagroup.com
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
---
Changes in v2:
 - change Ezra's email address (Ezra Buehler)
 - some cleanups (David Hildenbrand)
arch/arm/mm/fault-armv.c | 38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 2bec87c3327d2..ea4c4e15f0d31 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 +122,18 @@ 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 pmd_start_addr, pmd_end_addr;
    pgoff_t pgoff;
    int aliases = 0;
pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
+	pmd_start_addr = ALIGN_DOWN(addr, PMD_SIZE);
+	pmd_end_addr = pmd_start_addr + PMD_SIZE;
/*
     * If we have any shared mappings that are in the same mm
@@ -141,6 +142,14 @@ 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) {
+		/*
+		 * 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);
+		unsigned long mpnt_addr;
+
    	/*
    	 * If this VMA is not in our MM, we can ignore it.
    	 * Note that we intentionally mask out the VMA
@@ -151,7 +160,12 @@ 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;
+
+		/* Avoid deadlocks by not grabbing the same PTE lock again. */
+		if (mpnt_addr >= pmd_start_addr && mpnt_addr < pmd_end_addr)
+			need_lock = false;
+		aliases += adjust_pte(mpnt, mpnt_addr, pfn, need_lock);
    }
    flush_dcache_mmap_unlock(mapping);
    if (aliases)
@@ -194,7 +208,7 @@ void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma,
    	__flush_dcache_folio(mapping, folio);
    if (mapping) {
    	if (cache_is_vivt())
-			make_coherent(mapping, vma, addr, ptep, pfn, vmf);
+			make_coherent(mapping, vma, addr, ptep, pfn);
    	else if (vma->vm_flags & VM_EXEC)
    		__flush_icache_all();
    }
-- 
2.20.1



    