From 85900ea51577e31b186e523c8f4e068c79ecc7d3 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Tue, 12 Dec 2017 07:56:42 -0800 Subject: [PATCH] x86/pti: Map the vsyscall page if needed Make VSYSCALLs work fully in PTI mode by mapping them properly to the user space visible page tables. [ tglx: Hide unused functions (Patch by Arnd Bergmann) ] Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: David Laight Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Kees Cook Cc: Linus Torvalds Cc: Peter Zijlstra Signed-off-by: Ingo Molnar --- arch/x86/entry/vsyscall/vsyscall_64.c | 6 +-- arch/x86/include/asm/vsyscall.h | 1 + arch/x86/mm/pti.c | 65 +++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 3 deletions(-) diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index 1faf40f2dda9..577fa8adb785 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -344,14 +344,14 @@ int in_gate_area_no_mm(unsigned long addr) * vsyscalls but leave the page not present. If so, we skip calling * this. */ -static void __init set_vsyscall_pgtable_user_bits(void) +void __init set_vsyscall_pgtable_user_bits(pgd_t *root) { pgd_t *pgd; p4d_t *p4d; pud_t *pud; pmd_t *pmd; - pgd = pgd_offset_k(VSYSCALL_ADDR); + pgd = pgd_offset_pgd(root, VSYSCALL_ADDR); set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER)); p4d = p4d_offset(pgd, VSYSCALL_ADDR); #if CONFIG_PGTABLE_LEVELS >= 5 @@ -373,7 +373,7 @@ void __init map_vsyscall(void) vsyscall_mode == NATIVE ? PAGE_KERNEL_VSYSCALL : PAGE_KERNEL_VVAR); - set_vsyscall_pgtable_user_bits(); + set_vsyscall_pgtable_user_bits(swapper_pg_dir); } BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h index d9a7c659009c..b986b2ca688a 100644 --- a/arch/x86/include/asm/vsyscall.h +++ b/arch/x86/include/asm/vsyscall.h @@ -7,6 +7,7 @@ #ifdef CONFIG_X86_VSYSCALL_EMULATION extern void map_vsyscall(void); +extern void set_vsyscall_pgtable_user_bits(pgd_t *root); /* * Called on instruction fetch fault in vsyscall page. diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index b1c38ef9fbbb..bce8aea65606 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -38,6 +38,7 @@ #include #include +#include #include #include #include @@ -223,6 +224,69 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) return pmd_offset(pud, address); } +#ifdef CONFIG_X86_VSYSCALL_EMULATION +/* + * Walk the shadow copy of the page tables (optionally) trying to allocate + * page table pages on the way down. Does not support large pages. + * + * Note: this is only used when mapping *new* kernel data into the + * user/shadow page tables. It is never used for userspace data. + * + * Returns a pointer to a PTE on success, or NULL on failure. + */ +static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address) +{ + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + pmd_t *pmd = pti_user_pagetable_walk_pmd(address); + pte_t *pte; + + /* We can't do anything sensible if we hit a large mapping. */ + if (pmd_large(*pmd)) { + WARN_ON(1); + return NULL; + } + + if (pmd_none(*pmd)) { + unsigned long new_pte_page = __get_free_page(gfp); + if (!new_pte_page) + return NULL; + + if (pmd_none(*pmd)) { + set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page))); + new_pte_page = 0; + } + if (new_pte_page) + free_page(new_pte_page); + } + + pte = pte_offset_kernel(pmd, address); + if (pte_flags(*pte) & _PAGE_USER) { + WARN_ONCE(1, "attempt to walk to user pte\n"); + return NULL; + } + return pte; +} + +static void __init pti_setup_vsyscall(void) +{ + pte_t *pte, *target_pte; + unsigned int level; + + pte = lookup_address(VSYSCALL_ADDR, &level); + if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte)) + return; + + target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR); + if (WARN_ON(!target_pte)) + return; + + *target_pte = *pte; + set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir)); +} +#else +static void __init pti_setup_vsyscall(void) { } +#endif + static void __init pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear) { @@ -319,4 +383,5 @@ void __init pti_init(void) pti_clone_user_shared(); pti_clone_entry_text(); pti_setup_espfix64(); + pti_setup_vsyscall(); }