[PATCH v3 08/17] arm: pgtable: move pagetable_dtor() to __tlb_remove_table()

Qi Zheng
2024-12-23T09:44:45Z

Move pagetable_dtor() to __tlb_remove_table(), so that ptlock and page
table pages can be freed together (regardless of whether RCU is used).
This prevents the use-after-free problem where the ptlock is freed
immediately but the page table pages is freed later via RCU.

Page tables shouldn't have swap cache, so use pagetable_free() instead of
free_page_and_swap_cache() to free page table pages.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
---
arch/arm/include/asm/tlb.h | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index ef79bf1e8563f..264ab635e807a 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -26,12 +26,14 @@

#else /* !CONFIG_MMU */

-#include <linux/swap.h>
#include <asm/tlbflush.h>

static inline void __tlb_remove_table(void *_table)
{
- free_page_and_swap_cache((struct page *)_table);
+ struct ptdesc *ptdesc = (struct ptdesc *)_table;
+
+ pagetable_dtor(ptdesc);
+ pagetable_free(ptdesc);
}

#include <asm-generic/tlb.h>
@@ -41,8 +43,6 @@ __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte, unsigned long addr)
{
struct ptdesc *ptdesc = page_ptdesc(pte);

- pagetable_dtor(ptdesc);
-
#ifndef CONFIG_ARM_LPAE
/*
* With the classic ARM MMU, a pte page has two corresponding pmd
@@ -61,7 +61,6 @@ __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp, unsigned long addr)
#ifdef CONFIG_ARM_LPAE
struct ptdesc *ptdesc = virt_to_ptdesc(pmdp);

- pagetable_dtor(ptdesc);
tlb_remove_ptdesc(tlb, ptdesc);
#endif
}
--
2.20.1