blob: 60c48f5d6b0eede5ed2456a8196fc7d9e8187afe [file] [log] [blame]
/*
* Copyright(c) 2017 Intel Corporation. All rights reserved.
*
* 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.
*
* 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 <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
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);
}
void __init pti_check_boottime_disable(void)
{
char arg[5];
int ret;
if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
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_print_if_insecure("disabled on command line.");
return;
}
if (ret == 2 && !strncmp(arg, "on", 2)) {
pti_print_if_secure("force enabled on command line.");
goto enable;
}
if (ret == 4 && !strncmp(arg, "auto", 4))
goto autosel;
}
if (cmdline_find_option_bool(boot_command_line, "nopti")) {
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_pgd(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 __init 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 __init 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);
}
#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 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;
}
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)
{
unsigned long addr;
/*
* Clone the populated PMDs which cover start to end. These PMD areas
* can have holes.
*/
for (addr = start; addr < end; addr += PMD_SIZE) {
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))
continue;
pmd = pmd_offset(pud, addr);
if (pmd_none(*pmd))
continue;
target_pmd = pti_user_pagetable_walk_pmd(addr);
if (WARN_ON(!target_pmd))
return;
/*
* Copy the PMD. That is, the kernelmode and usermode
* tables will share the last-level page tables of this
* address range
*/
*target_pmd = pmd_clear_flags(*pmd, clear);
}
}
/*
* 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 into the user space visible page table.
*/
static void __init pti_clone_user_shared(void)
{
pti_clone_p4d(CPU_ENTRY_AREA_BASE);
}
/*
* Clone the ESPFIX P4D into the user space visinble 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 __init pti_clone_entry_text(void)
{
pti_clone_pmds((unsigned long) __entry_text_start,
(unsigned long) __irqentry_text_end,
_PAGE_RW | _PAGE_GLOBAL);
}
/*
* Initialize kernel page table isolation
*/
void __init pti_init(void)
{
if (!static_cpu_has(X86_FEATURE_PTI))
return;
pr_info("enabled\n");
pti_clone_user_shared();
pti_clone_entry_text();
pti_setup_espfix64();
pti_setup_vsyscall();
}