From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> commit c48b5a4cf3125adb679e28ef093f66ff81368d05 upstream. So it turns out that we have to do two passes of pti_clone_entry_text(), once before initcalls, such that device and late initcalls can use user-mode-helper / modprobe and once after free_initmem() / mark_readonly(). Now obviously mark_readonly() can cause PMD splits, and pti_clone_pgtable() doesn't like that much. Allow the late clone to split PMDs so that pagetables stay in sync. [peterz: Changelog and comments] Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20240806184843.GX37996@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/pti.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-) --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -241,7 +241,7 @@ static pmd_t *pti_user_pagetable_walk_pm * * Returns a pointer to a PTE on success, or NULL on failure. */ -static pte_t *pti_user_pagetable_walk_pte(unsigned long address) +static pte_t *pti_user_pagetable_walk_pte(unsigned long address, bool late_text) { gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); pmd_t *pmd; @@ -251,10 +251,15 @@ static pte_t *pti_user_pagetable_walk_pt if (!pmd) return NULL; - /* We can't do anything sensible if we hit a large mapping. */ + /* Large PMD mapping found */ if (pmd_large(*pmd)) { - WARN_ON(1); - return NULL; + /* Clear the PMD if we hit a large mapping from the first round */ + if (late_text) { + set_pmd(pmd, __pmd(0)); + } else { + WARN_ON_ONCE(1); + return NULL; + } } if (pmd_none(*pmd)) { @@ -283,7 +288,7 @@ static void __init pti_setup_vsyscall(vo if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte)) return; - target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR); + target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR, false); if (WARN_ON(!target_pte)) return; @@ -301,7 +306,7 @@ enum pti_clone_level { static void pti_clone_pgtable(unsigned long start, unsigned long end, - enum pti_clone_level level) + enum pti_clone_level level, bool late_text) { unsigned long addr; @@ -390,7 +395,7 @@ pti_clone_pgtable(unsigned long start, u return; /* Allocate PTE in the user page-table */ - target_pte = pti_user_pagetable_walk_pte(addr); + target_pte = pti_user_pagetable_walk_pte(addr, late_text); if (WARN_ON(!target_pte)) return; @@ -453,7 +458,7 @@ static void __init pti_clone_user_shared phys_addr_t pa = per_cpu_ptr_to_phys((void *)va); pte_t *target_pte; - target_pte = pti_user_pagetable_walk_pte(va); + target_pte = pti_user_pagetable_walk_pte(va, false); if (WARN_ON(!target_pte)) return; @@ -476,7 +481,7 @@ static void __init pti_clone_user_shared start = CPU_ENTRY_AREA_BASE; end = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES); - pti_clone_pgtable(start, end, PTI_CLONE_PMD); + pti_clone_pgtable(start, end, PTI_CLONE_PMD, false); } #endif /* CONFIG_X86_64 */ @@ -493,11 +498,11 @@ static void __init pti_setup_espfix64(vo /* * Clone the populated PMDs of the entry text and force it RO. */ -static void pti_clone_entry_text(void) +static void pti_clone_entry_text(bool late) { pti_clone_pgtable((unsigned long) __entry_text_start, (unsigned long) __entry_text_end, - PTI_LEVEL_KERNEL_IMAGE); + PTI_LEVEL_KERNEL_IMAGE, late); } /* @@ -572,7 +577,7 @@ static void pti_clone_kernel_text(void) * pti_set_kernel_image_nonglobal() did to clear the * global bit. */ - pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE); + pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE, false); /* * pti_clone_pgtable() will set the global bit in any PMDs @@ -639,8 +644,15 @@ void __init pti_init(void) /* Undo all global bits from the init pagetables in head_64.S: */ pti_set_kernel_image_nonglobal(); + /* Replace some of the global bits just for shared entry text: */ - pti_clone_entry_text(); + /* + * This is very early in boot. Device and Late initcalls can do + * modprobe before free_initmem() and mark_readonly(). This + * pti_clone_entry_text() allows those user-mode-helpers to function, + * but notably the text is still RW. + */ + pti_clone_entry_text(false); pti_setup_espfix64(); pti_setup_vsyscall(); } @@ -657,10 +669,11 @@ void pti_finalize(void) if (!boot_cpu_has(X86_FEATURE_PTI)) return; /* - * We need to clone everything (again) that maps parts of the - * kernel image. + * This is after free_initmem() (all initcalls are done) and we've done + * mark_readonly(). Text is now NX which might've split some PMDs + * relative to the early clone. */ - pti_clone_entry_text(); + pti_clone_entry_text(true); pti_clone_kernel_text(); debug_checkwx_user(); Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are queue-5.10/rtmutex-drop-rt_mutex-wait_lock-before-scheduling.patch queue-5.10/x86-mm-fix-pti-for-i386-some-more.patch queue-5.10/irqchip-armada-370-xp-do-not-allow-mapping-irq-0-and.patch queue-5.10/smp-add-missing-destroy_work_on_stack-call-in-smp_ca.patch queue-5.10/irqchip-gic-v2m-fix-refcount-leak-in-gicv2m_of_init.patch
