The patch titled Subject: arm: pgtable: fix NULL pointer dereference issue has been added to the -mm mm-hotfixes-unstable branch. Its filename is arm-pgtable-fix-null-pointer-dereference-issue.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Qi Zheng zhengqi.arch@bytedance.com Subject: arm: pgtable: fix NULL pointer dereference issue Date: Wed, 12 Feb 2025 14:40:02 +0800
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.
Link: https://lkml.kernel.org/r/20250212064002.55598-1-zhengqi.arch@bytedance.com Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()") Signed-off-by: Qi Zheng zhengqi.arch@bytedance.com Reported-by: Ezra Buehler ezra@easyb.ch Closes: https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cL... Cc: David Hildenbrand david@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Muchun Song muchun.song@linux.dev Cc: Russell King linux@armlinux.org.uk Cc: Ryan Roberts ryan.roberts@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
arch/arm/mm/fault-armv.c | 40 +++++++++++++++++++++++++------------ 1 file changed, 28 insertions(+), 12 deletions(-)
--- a/arch/arm/mm/fault-armv.c~arm-pgtable-fix-null-pointer-dereference-issue +++ a/arch/arm/mm/fault-armv.c @@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_ }
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 @@ again: 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 @@ again:
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 @@ again:
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);
/* * If we have any shared mappings that are in the same mm @@ -141,6 +141,14 @@ make_coherent(struct address_space *mapp */ 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); + /* * 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 *mapp 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. + */ + if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE) + need_lock = false; + aliases += adjust_pte(mpnt, mpnt_addr, pfn, need_lock); } flush_dcache_mmap_unlock(mapping); if (aliases) @@ -194,7 +210,7 @@ void update_mmu_cache_range(struct vm_fa __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(); } _
Patches currently in -mm which might be from zhengqi.arch@bytedance.com are
mm-pgtable-fix-incorrect-reclaim-of-non-empty-pte-pages.patch arm-pgtable-fix-null-pointer-dereference-issue.patch