linux/arch/x86/mm/pti.c
Thomas Gleixner 5b497af42f treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 295
Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of version 2 of the gnu general public license as
  published by the free software foundation this program is
  distributed in the hope that it will be useful but without any
  warranty without even the implied warranty of merchantability or
  fitness for a particular purpose see the gnu general public license
  for more details

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 64 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190529141901.894819585@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-05 17:36:38 +02:00

678 lines
18 KiB
C

// 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 <richard.fellner@student.tugraz.at>
* Signed-off-by: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
* Signed-off-by: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
* Signed-off-by: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
*
* Major changes to the original code by: Dave Hansen <dave.hansen@intel.com>
* Mostly rewritten by Thomas Gleixner <tglx@linutronix.de> and
* Andy Lutomirsky <luto@amacapital.net>
*/
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/bug.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/cpu.h>
#include <asm/cpufeature.h>
#include <asm/hypervisor.h>
#include <asm/vsyscall.h>
#include <asm/cmdline.h>
#include <asm/pti.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/desc.h>
#include <asm/sections.h>
#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)) {
addr += PUD_SIZE;
continue;
}
pmd = pmd_offset(pud, addr);
if (pmd_none(*pmd)) {
addr += 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 consistentency 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 to be able to find the
* thread stack and needs one word of scratch space in which
* to spill a register. All of this lives in the TSS, in
* the sp1 and sp2 slots.
*
* This is done for all possible CPUs during boot to ensure
* that it's propagated to all mms. If we were to add one of
* these mappings during CPU hotplug, we would need to take
* some measure to make sure that every mm that subsequently
* ran on that CPU would have the relevant PGD entry in its
* pagetables. The usual vmalloc_fault() mechanism would not
* work for page faults taken in entry_SYSCALL_64 before RSP
* is set up.
*/
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 and irqentry text and force it RO.
*/
static void pti_clone_entry_text(void)
{
pti_clone_pgtable((unsigned long) __entry_text_start,
(unsigned long) __irqentry_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 litlle 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_GCC_PLUGIN_RANDSTRUCT))
return false;
return true;
}
/*
* This is the only user for these and it is not arch-generic
* like the other set_memory.h functions. Just extern them.
*/
extern int set_memory_nonglobal(unsigned long addr, int numpages);
extern int set_memory_global(unsigned long addr, int numpages);
/*
* 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)__stop___ex_table);
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)
{
/*
* We need to clone everything (again) that maps parts of the
* kernel image.
*/
pti_clone_entry_text();
pti_clone_kernel_text();
debug_checkwx_user();
}