[PATCH 01/23] arm: allow pte_offset_map[_lock]() to fail

Hugh Dickins
2023-05-10T04:43:04Z

In rare transient cases, not yet made possible, pte_offset_map() and
pte_offset_map_lock() may not find a page table: handle appropriately.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
arch/arm/lib/uaccess_with_memcpy.c | 3 +++
arch/arm/mm/fault-armv.c | 5 ++++-
arch/arm/mm/fault.c | 3 +++
3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index e4c2677cc1e9..2f6163f05e93 100644
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -74,6 +74,9 @@ pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
return 0;

pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
+ if (unlikely(!pte))
+ return 0;
+
if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
!pte_write(*pte) || !pte_dirty(*pte))) {
pte_unmap_unlock(pte, ptl);
diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 0e49154454a6..ca5302b0b7ee 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -117,8 +117,11 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
* must use the nested version. This also means we need to
* open-code the spin-locking.
*/
- ptl = pte_lockptr(vma->vm_mm, pmd);
pte = pte_offset_map(pmd, address);
+ if (!pte)
+ return 0;
+
+ ptl = pte_lockptr(vma->vm_mm, pmd);
do_pte_lock(ptl);

ret = do_adjust_pte(vma, address, pfn, pte);
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 2418f1efabd8..83598649a094 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -85,6 +85,9 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
break;

pte = pte_offset_map(pmd, addr);
+ if (!pte)
+ break;
+
pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
#ifndef CONFIG_ARM_LPAE
pr_cont(", *ppte=%08llx",
--
2.35.3