5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Karl Mehltretter [ Upstream commit a77644d009dece1104b6fcc6e322b0e4503db0d6 ] show_pte() walks page tables locklessly and can run with interrupts enabled. A concurrent teardown can free a table page while it is being walked. It can also clear a parent entry after show_pte() checked it; the regular pXd_offset() helpers then reread the cleared entry and can derive a bogus lower-level pointer and fault again. Use the lockless offset helpers with the saved parent entries, as gup_fast() does, and pass the saved PMD to pte_offset_map(). For task page tables, arm64 selects MMU_GATHER_RCU_TABLE_FREE. Disable local interrupts around the walk to hold off RCU-deferred table frees and block the tlb_remove_table_sync_one() IPI until the walk is finished. Place the IRQ guard after the header print. This does not make the output a consistent snapshot, but prevents the task page-table walk from dereferencing a released table page or deriving a pointer from a different parent value. Fixes: 1d18c47c735e ("arm64: MMU fault handling and page table management") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter Signed-off-by: Will Deacon [ replaced guard(irqsave)() with explicit local_irq_save()/local_irq_restore() to avoid declaration-after-statement warnings. ] Signed-off-by: Sasha Levin --- arch/arm64/mm/fault.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index d8baedd160de0..edf82cced64dd 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include #include @@ -116,6 +117,7 @@ static inline unsigned long mm_to_pgd_phys(struct mm_struct *mm) static void show_pte(unsigned long addr) { struct mm_struct *mm; + unsigned long flags; pgd_t *pgdp; pgd_t pgd; @@ -139,6 +141,9 @@ static void show_pte(unsigned long addr) pr_alert("%s pgtable: %luk pages, %llu-bit VAs, pgdp=%016lx\n", mm == &init_mm ? "swapper" : "user", PAGE_SIZE / SZ_1K, vabits_actual, mm_to_pgd_phys(mm)); + + local_irq_save(flags); + pgdp = pgd_offset(mm, addr); pgd = READ_ONCE(*pgdp); pr_alert("[%016lx] pgd=%016llx", addr, pgd_val(pgd)); @@ -152,31 +157,32 @@ static void show_pte(unsigned long addr) if (pgd_none(pgd) || pgd_bad(pgd)) break; - p4dp = p4d_offset(pgdp, addr); + p4dp = p4d_offset_lockless(pgdp, pgd, addr); p4d = READ_ONCE(*p4dp); pr_cont(", p4d=%016llx", p4d_val(p4d)); if (p4d_none(p4d) || p4d_bad(p4d)) break; - pudp = pud_offset(p4dp, addr); + pudp = pud_offset_lockless(p4dp, p4d, addr); pud = READ_ONCE(*pudp); pr_cont(", pud=%016llx", pud_val(pud)); if (pud_none(pud) || pud_bad(pud)) break; - pmdp = pmd_offset(pudp, addr); + pmdp = pmd_offset_lockless(pudp, pud, addr); pmd = READ_ONCE(*pmdp); pr_cont(", pmd=%016llx", pmd_val(pmd)); if (pmd_none(pmd) || pmd_bad(pmd)) break; - ptep = pte_offset_map(pmdp, addr); + ptep = pte_offset_map(&pmd, addr); pte = READ_ONCE(*ptep); pr_cont(", pte=%016llx", pte_val(pte)); pte_unmap(ptep); } while(0); pr_cont("\n"); + local_irq_restore(flags); } /* -- 2.53.0