From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- arch/x86/mm/pti.c | 666 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 666 insertions(+) create mode 100644 arch/x86/mm/pti.c (limited to 'arch/x86/mm/pti.c') diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c new file mode 100644 index 000000000..ffe3b3a08 --- /dev/null +++ b/arch/x86/mm/pti.c @@ -0,0 +1,666 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright(c) 2017 Intel Corporation. All rights reserved. + * + * This code is based in part on work published here: + * + * https://github.com/IAIK/KAISER + * + * The original work was written by and and signed off by for the Linux + * kernel by: + * + * Signed-off-by: Richard Fellner + * Signed-off-by: Moritz Lipp + * Signed-off-by: Daniel Gruss + * Signed-off-by: Michael Schwarz + * + * Major changes to the original code by: Dave Hansen + * Mostly rewritten by Thomas Gleixner and + * Andy Lutomirsky + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#undef pr_fmt +#define pr_fmt(fmt) "Kernel/User page tables isolation: " fmt + +/* Backporting helper */ +#ifndef __GFP_NOTRACK +#define __GFP_NOTRACK 0 +#endif + +/* + * Define the page-table levels we clone for user-space on 32 + * and 64 bit. + */ +#ifdef CONFIG_X86_64 +#define PTI_LEVEL_KERNEL_IMAGE PTI_CLONE_PMD +#else +#define PTI_LEVEL_KERNEL_IMAGE PTI_CLONE_PTE +#endif + +static void __init pti_print_if_insecure(const char *reason) +{ + if (boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN)) + pr_info("%s\n", reason); +} + +static void __init pti_print_if_secure(const char *reason) +{ + if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN)) + pr_info("%s\n", reason); +} + +static enum pti_mode { + PTI_AUTO = 0, + PTI_FORCE_OFF, + PTI_FORCE_ON +} pti_mode; + +void __init pti_check_boottime_disable(void) +{ + char arg[5]; + int ret; + + /* Assume mode is auto unless overridden. */ + pti_mode = PTI_AUTO; + + if (hypervisor_is_type(X86_HYPER_XEN_PV)) { + pti_mode = PTI_FORCE_OFF; + pti_print_if_insecure("disabled on XEN PV."); + return; + } + + ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg)); + if (ret > 0) { + if (ret == 3 && !strncmp(arg, "off", 3)) { + pti_mode = PTI_FORCE_OFF; + pti_print_if_insecure("disabled on command line."); + return; + } + if (ret == 2 && !strncmp(arg, "on", 2)) { + pti_mode = PTI_FORCE_ON; + pti_print_if_secure("force enabled on command line."); + goto enable; + } + if (ret == 4 && !strncmp(arg, "auto", 4)) { + pti_mode = PTI_AUTO; + goto autosel; + } + } + + if (cmdline_find_option_bool(boot_command_line, "nopti") || + cpu_mitigations_off()) { + pti_mode = PTI_FORCE_OFF; + pti_print_if_insecure("disabled on command line."); + return; + } + +autosel: + if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN)) + return; +enable: + setup_force_cpu_cap(X86_FEATURE_PTI); +} + +pgd_t __pti_set_user_pgtbl(pgd_t *pgdp, pgd_t pgd) +{ + /* + * Changes to the high (kernel) portion of the kernelmode page + * tables are not automatically propagated to the usermode tables. + * + * Users should keep in mind that, unlike the kernelmode tables, + * there is no vmalloc_fault equivalent for the usermode tables. + * Top-level entries added to init_mm's usermode pgd after boot + * will not be automatically propagated to other mms. + */ + if (!pgdp_maps_userspace(pgdp)) + return pgd; + + /* + * The user page tables get the full PGD, accessible from + * userspace: + */ + kernel_to_user_pgdp(pgdp)->pgd = pgd.pgd; + + /* + * If this is normal user memory, make it NX in the kernel + * pagetables so that, if we somehow screw up and return to + * usermode with the kernel CR3 loaded, we'll get a page fault + * instead of allowing user code to execute with the wrong CR3. + * + * As exceptions, we don't set NX if: + * - _PAGE_USER is not set. This could be an executable + * EFI runtime mapping or something similar, and the kernel + * may execute from it + * - we don't have NX support + * - we're clearing the PGD (i.e. the new pgd is not present). + */ + if ((pgd.pgd & (_PAGE_USER|_PAGE_PRESENT)) == (_PAGE_USER|_PAGE_PRESENT) && + (__supported_pte_mask & _PAGE_NX)) + pgd.pgd |= _PAGE_NX; + + /* return the copy of the PGD we want the kernel to use: */ + return pgd; +} + +/* + * Walk the user copy of the page tables (optionally) trying to allocate + * page table pages on the way down. + * + * Returns a pointer to a P4D on success, or NULL on failure. + */ +static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) +{ + pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address)); + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + + if (address < PAGE_OFFSET) { + WARN_ONCE(1, "attempt to walk user address\n"); + return NULL; + } + + if (pgd_none(*pgd)) { + unsigned long new_p4d_page = __get_free_page(gfp); + if (WARN_ON_ONCE(!new_p4d_page)) + return NULL; + + set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page))); + } + BUILD_BUG_ON(pgd_large(*pgd) != 0); + + return p4d_offset(pgd, address); +} + +/* + * Walk the user copy of the page tables (optionally) trying to allocate + * page table pages on the way down. + * + * Returns a pointer to a PMD on success, or NULL on failure. + */ +static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) +{ + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + p4d_t *p4d; + pud_t *pud; + + p4d = pti_user_pagetable_walk_p4d(address); + if (!p4d) + return NULL; + + BUILD_BUG_ON(p4d_large(*p4d) != 0); + if (p4d_none(*p4d)) { + unsigned long new_pud_page = __get_free_page(gfp); + if (WARN_ON_ONCE(!new_pud_page)) + return NULL; + + set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page))); + } + + pud = pud_offset(p4d, address); + /* The user page tables do not use large mappings: */ + if (pud_large(*pud)) { + WARN_ON(1); + return NULL; + } + if (pud_none(*pud)) { + unsigned long new_pmd_page = __get_free_page(gfp); + if (WARN_ON_ONCE(!new_pmd_page)) + return NULL; + + set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page))); + } + + return pmd_offset(pud, address); +} + +/* + * 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 pte_t *pti_user_pagetable_walk_pte(unsigned long address) +{ + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + pmd_t *pmd; + pte_t *pte; + + pmd = pti_user_pagetable_walk_pmd(address); + if (!pmd) + return NULL; + + /* 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; + + set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(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; +} + +#ifdef CONFIG_X86_VSYSCALL_EMULATION +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 + +enum pti_clone_level { + PTI_CLONE_PMD, + PTI_CLONE_PTE, +}; + +static void +pti_clone_pgtable(unsigned long start, unsigned long end, + enum pti_clone_level level) +{ + unsigned long addr; + + /* + * Clone the populated PMDs which cover start to end. These PMD areas + * can have holes. + */ + for (addr = start; addr < end;) { + pte_t *pte, *target_pte; + pmd_t *pmd, *target_pmd; + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + + /* Overflow check */ + if (addr < start) + break; + + pgd = pgd_offset_k(addr); + if (WARN_ON(pgd_none(*pgd))) + return; + p4d = p4d_offset(pgd, addr); + if (WARN_ON(p4d_none(*p4d))) + return; + + pud = pud_offset(p4d, addr); + if (pud_none(*pud)) { + WARN_ON_ONCE(addr & ~PUD_MASK); + addr = round_up(addr + 1, PUD_SIZE); + continue; + } + + pmd = pmd_offset(pud, addr); + if (pmd_none(*pmd)) { + WARN_ON_ONCE(addr & ~PMD_MASK); + addr = round_up(addr + 1, PMD_SIZE); + continue; + } + + if (pmd_large(*pmd) || level == PTI_CLONE_PMD) { + target_pmd = pti_user_pagetable_walk_pmd(addr); + if (WARN_ON(!target_pmd)) + return; + + /* + * Only clone present PMDs. This ensures only setting + * _PAGE_GLOBAL on present PMDs. This should only be + * called on well-known addresses anyway, so a non- + * present PMD would be a surprise. + */ + if (WARN_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT))) + return; + + /* + * Setting 'target_pmd' below creates a mapping in both + * the user and kernel page tables. It is effectively + * global, so set it as global in both copies. Note: + * the X86_FEATURE_PGE check is not _required_ because + * the CPU ignores _PAGE_GLOBAL when PGE is not + * supported. The check keeps consistency with + * code that only set this bit when supported. + */ + if (boot_cpu_has(X86_FEATURE_PGE)) + *pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL); + + /* + * Copy the PMD. That is, the kernelmode and usermode + * tables will share the last-level page tables of this + * address range + */ + *target_pmd = *pmd; + + addr += PMD_SIZE; + + } else if (level == PTI_CLONE_PTE) { + + /* Walk the page-table down to the pte level */ + pte = pte_offset_kernel(pmd, addr); + if (pte_none(*pte)) { + addr += PAGE_SIZE; + continue; + } + + /* Only clone present PTEs */ + if (WARN_ON(!(pte_flags(*pte) & _PAGE_PRESENT))) + return; + + /* Allocate PTE in the user page-table */ + target_pte = pti_user_pagetable_walk_pte(addr); + if (WARN_ON(!target_pte)) + return; + + /* Set GLOBAL bit in both PTEs */ + if (boot_cpu_has(X86_FEATURE_PGE)) + *pte = pte_set_flags(*pte, _PAGE_GLOBAL); + + /* Clone the PTE */ + *target_pte = *pte; + + addr += PAGE_SIZE; + + } else { + BUG(); + } + } +} + +#ifdef CONFIG_X86_64 +/* + * Clone a single p4d (i.e. a top-level entry on 4-level systems and a + * next-level entry on 5-level systems. + */ +static void __init pti_clone_p4d(unsigned long addr) +{ + p4d_t *kernel_p4d, *user_p4d; + pgd_t *kernel_pgd; + + user_p4d = pti_user_pagetable_walk_p4d(addr); + if (!user_p4d) + return; + + kernel_pgd = pgd_offset_k(addr); + kernel_p4d = p4d_offset(kernel_pgd, addr); + *user_p4d = *kernel_p4d; +} + +/* + * Clone the CPU_ENTRY_AREA and associated data into the user space visible + * page table. + */ +static void __init pti_clone_user_shared(void) +{ + unsigned int cpu; + + pti_clone_p4d(CPU_ENTRY_AREA_BASE); + + for_each_possible_cpu(cpu) { + /* + * The SYSCALL64 entry code needs one word of scratch space + * in which to spill a register. It lives in the sp2 slot + * of the CPU's TSS. + * + * This is done for all possible CPUs during boot to ensure + * that it's propagated to all mms. + */ + + unsigned long va = (unsigned long)&per_cpu(cpu_tss_rw, cpu); + phys_addr_t pa = per_cpu_ptr_to_phys((void *)va); + pte_t *target_pte; + + target_pte = pti_user_pagetable_walk_pte(va); + if (WARN_ON(!target_pte)) + return; + + *target_pte = pfn_pte(pa >> PAGE_SHIFT, PAGE_KERNEL); + } +} + +#else /* CONFIG_X86_64 */ + +/* + * On 32 bit PAE systems with 1GB of Kernel address space there is only + * one pgd/p4d for the whole kernel. Cloning that would map the whole + * address space into the user page-tables, making PTI useless. So clone + * the page-table on the PMD level to prevent that. + */ +static void __init pti_clone_user_shared(void) +{ + unsigned long start, end; + + start = CPU_ENTRY_AREA_BASE; + end = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES); + + pti_clone_pgtable(start, end, PTI_CLONE_PMD); +} +#endif /* CONFIG_X86_64 */ + +/* + * Clone the ESPFIX P4D into the user space visible page table + */ +static void __init pti_setup_espfix64(void) +{ +#ifdef CONFIG_X86_ESPFIX64 + pti_clone_p4d(ESPFIX_BASE_ADDR); +#endif +} + +/* + * Clone the populated PMDs of the entry text and force it RO. + */ +static void pti_clone_entry_text(void) +{ + pti_clone_pgtable((unsigned long) __entry_text_start, + (unsigned long) __entry_text_end, + PTI_CLONE_PMD); +} + +/* + * Global pages and PCIDs are both ways to make kernel TLB entries + * live longer, reduce TLB misses and improve kernel performance. + * But, leaving all kernel text Global makes it potentially accessible + * to Meltdown-style attacks which make it trivial to find gadgets or + * defeat KASLR. + * + * Only use global pages when it is really worth it. + */ +static inline bool pti_kernel_image_global_ok(void) +{ + /* + * Systems with PCIDs get little benefit from global + * kernel text and are not worth the downsides. + */ + if (cpu_feature_enabled(X86_FEATURE_PCID)) + return false; + + /* + * Only do global kernel image for pti=auto. Do the most + * secure thing (not global) if pti=on specified. + */ + if (pti_mode != PTI_AUTO) + return false; + + /* + * K8 may not tolerate the cleared _PAGE_RW on the userspace + * global kernel image pages. Do the safe thing (disable + * global kernel image). This is unlikely to ever be + * noticed because PTI is disabled by default on AMD CPUs. + */ + if (boot_cpu_has(X86_FEATURE_K8)) + return false; + + /* + * RANDSTRUCT derives its hardening benefits from the + * attacker's lack of knowledge about the layout of kernel + * data structures. Keep the kernel image non-global in + * cases where RANDSTRUCT is in use to help keep the layout a + * secret. + */ + if (IS_ENABLED(CONFIG_RANDSTRUCT)) + return false; + + return true; +} + +/* + * For some configurations, map all of kernel text into the user page + * tables. This reduces TLB misses, especially on non-PCID systems. + */ +static void pti_clone_kernel_text(void) +{ + /* + * rodata is part of the kernel image and is normally + * readable on the filesystem or on the web. But, do not + * clone the areas past rodata, they might contain secrets. + */ + unsigned long start = PFN_ALIGN(_text); + unsigned long end_clone = (unsigned long)__end_rodata_aligned; + unsigned long end_global = PFN_ALIGN((unsigned long)_etext); + + if (!pti_kernel_image_global_ok()) + return; + + pr_debug("mapping partial kernel image into user address space\n"); + + /* + * Note that this will undo _some_ of the work that + * pti_set_kernel_image_nonglobal() did to clear the + * global bit. + */ + pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE); + + /* + * pti_clone_pgtable() will set the global bit in any PMDs + * that it clones, but we also need to get any PTEs in + * the last level for areas that are not huge-page-aligned. + */ + + /* Set the global bit for normal non-__init kernel text: */ + set_memory_global(start, (end_global - start) >> PAGE_SHIFT); +} + +static void pti_set_kernel_image_nonglobal(void) +{ + /* + * The identity map is created with PMDs, regardless of the + * actual length of the kernel. We need to clear + * _PAGE_GLOBAL up to a PMD boundary, not just to the end + * of the image. + */ + unsigned long start = PFN_ALIGN(_text); + unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE); + + /* + * This clears _PAGE_GLOBAL from the entire kernel image. + * pti_clone_kernel_text() map put _PAGE_GLOBAL back for + * areas that are mapped to userspace. + */ + set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT); +} + +/* + * Initialize kernel page table isolation + */ +void __init pti_init(void) +{ + if (!boot_cpu_has(X86_FEATURE_PTI)) + return; + + pr_info("enabled\n"); + +#ifdef CONFIG_X86_32 + /* + * We check for X86_FEATURE_PCID here. But the init-code will + * clear the feature flag on 32 bit because the feature is not + * supported on 32 bit anyway. To print the warning we need to + * check with cpuid directly again. + */ + if (cpuid_ecx(0x1) & BIT(17)) { + /* Use printk to work around pr_fmt() */ + printk(KERN_WARNING "\n"); + printk(KERN_WARNING "************************************************************\n"); + printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! **\n"); + printk(KERN_WARNING "** **\n"); + printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit PCID-capable CPU. **\n"); + printk(KERN_WARNING "** Your performance will increase dramatically if you **\n"); + printk(KERN_WARNING "** switch to a 64-bit kernel! **\n"); + printk(KERN_WARNING "** **\n"); + printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! **\n"); + printk(KERN_WARNING "************************************************************\n"); + } +#endif + + pti_clone_user_shared(); + + /* 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(); + pti_setup_espfix64(); + pti_setup_vsyscall(); +} + +/* + * Finalize the kernel mappings in the userspace page-table. Some of the + * mappings for the kernel image might have changed since pti_init() + * cloned them. This is because parts of the kernel image have been + * mapped RO and/or NX. These changes need to be cloned again to the + * userspace page-table. + */ +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. + */ + pti_clone_entry_text(); + pti_clone_kernel_text(); + + debug_checkwx_user(); +} -- cgit v1.2.3