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@xxxxxxxx>
Closes: https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@xxxxxxxxxxxxxx/
Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
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;
--
Cheers,
David / dhildenb
