[PATCH v3 11/17] x86: pgtable: move pagetable_dtor() to __tlb_remove_table()

Qi Zheng
2024-12-23T09:45:24Z

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: x86@kernel.org
---
arch/x86/include/asm/tlb.h | 17 ++++++++++-------
arch/x86/kernel/paravirt.c | 1 +
arch/x86/mm/pgtable.c | 12 ++----------
3 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
index 73f0786181cc9..f64730be5ad67 100644
--- a/arch/x86/include/asm/tlb.h
+++ b/arch/x86/include/asm/tlb.h
@@ -31,24 +31,27 @@ static inline void tlb_flush(struct mmu_gather *tlb)
*/
static inline void __tlb_remove_table(void *table)
{
- free_page_and_swap_cache(table);
+ struct ptdesc *ptdesc = (struct ptdesc *)table;
+
+ pagetable_dtor(ptdesc);
+ pagetable_free(ptdesc);
}

#ifdef CONFIG_PT_RECLAIM
static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
{
- struct page *page;
+ struct ptdesc *ptdesc;

- page = container_of(head, struct page, rcu_head);
- put_page(page);
+ ptdesc = container_of(head, struct ptdesc, pt_rcu_head);
+ __tlb_remove_table(ptdesc);
}

static inline void __tlb_remove_table_one(void *table)
{
- struct page *page;
+ struct ptdesc *ptdesc;

- page = table;
- call_rcu(&page->rcu_head, __tlb_remove_table_one_rcu);
+ ptdesc = table;
+ call_rcu(&ptdesc->pt_rcu_head, __tlb_remove_table_one_rcu);
}
#define __tlb_remove_table_one __tlb_remove_table_one
#endif /* CONFIG_PT_RECLAIM */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 7bdcf152778c0..46d5d325483b0 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -62,6 +62,7 @@ void __init native_pv_lock_init(void)
#ifndef CONFIG_PT_RECLAIM
static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)
{
+ pagetable_dtor(table);
tlb_remove_page(tlb, table);
}
#else
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index a6cd9660e29ec..a0b0e501ba663 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -23,6 +23,7 @@ EXPORT_SYMBOL(physical_mask);
static inline
void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)
{
+ pagetable_dtor(table);
tlb_remove_page(tlb, table);
}
#else
@@ -60,7 +61,6 @@ early_param("userpte", setup_userpte);

void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
{
- pagetable_dtor(page_ptdesc(pte));
paravirt_release_pte(page_to_pfn(pte));
paravirt_tlb_remove_table(tlb, pte);
}
@@ -68,7 +68,6 @@ void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
#if CONFIG_PGTABLE_LEVELS > 2
void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
{
- struct ptdesc *ptdesc = virt_to_ptdesc(pmd);
paravirt_release_pmd(__pa(pmd) >> PAGE_SHIFT);
/*
* NOTE! For PAE, any changes to the top page-directory-pointer-table
@@ -77,16 +76,12 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
#ifdef CONFIG_X86_PAE
tlb->need_flush_all = 1;
#endif
- pagetable_dtor(ptdesc);
- paravirt_tlb_remove_table(tlb, ptdesc_page(ptdesc));
+ paravirt_tlb_remove_table(tlb, virt_to_page(pmd));
}

#if CONFIG_PGTABLE_LEVELS > 3
void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
{
- struct ptdesc *ptdesc = virt_to_ptdesc(pud);
-
- pagetable_dtor(ptdesc);
paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
paravirt_tlb_remove_table(tlb, virt_to_page(pud));
}
@@ -94,9 +89,6 @@ void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
#if CONFIG_PGTABLE_LEVELS > 4
void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d)
{
- struct ptdesc *ptdesc = virt_to_ptdesc(p4d);
-
- pagetable_dtor(ptdesc);
paravirt_release_p4d(__pa(p4d) >> PAGE_SHIFT);
paravirt_tlb_remove_table(tlb, virt_to_page(p4d));
}
--
2.20.1