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-rw-r--r--arch/x86/mm/kaiser.c484
1 files changed, 484 insertions, 0 deletions
diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
new file mode 100644
index 000000000000..7a72e32e4806
--- /dev/null
+++ b/arch/x86/mm/kaiser.c
@@ -0,0 +1,484 @@
+#include <linux/bug.h>
+#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/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+#include <linux/ftrace.h>
+
+#undef pr_fmt
+#define pr_fmt(fmt) "Kernel/User page tables isolation: " fmt
+
+#include <asm/kaiser.h>
+#include <asm/tlbflush.h> /* to verify its kaiser declarations */
+#include <asm/pgtable.h>
+#include <asm/pgalloc.h>
+#include <asm/desc.h>
+#include <asm/cmdline.h>
+#include <asm/vsyscall.h>
+
+int kaiser_enabled __read_mostly = 1;
+EXPORT_SYMBOL(kaiser_enabled); /* for inlined TLB flush functions */
+
+__visible
+DEFINE_PER_CPU_USER_MAPPED(unsigned long, unsafe_stack_register_backup);
+
+/*
+ * These can have bit 63 set, so we can not just use a plain "or"
+ * instruction to get their value or'd into CR3. It would take
+ * another register. So, we use a memory reference to these instead.
+ *
+ * This is also handy because systems that do not support PCIDs
+ * just end up or'ing a 0 into their CR3, which does no harm.
+ */
+DEFINE_PER_CPU(unsigned long, x86_cr3_pcid_user);
+
+/*
+ * At runtime, the only things we map are some things for CPU
+ * hotplug, and stacks for new processes. No two CPUs will ever
+ * be populating the same addresses, so we only need to ensure
+ * that we protect between two CPUs trying to allocate and
+ * populate the same page table page.
+ *
+ * Only take this lock when doing a set_p[4um]d(), but it is not
+ * needed for doing a set_pte(). We assume that only the *owner*
+ * of a given allocation will be doing this for _their_
+ * allocation.
+ *
+ * This ensures that once a system has been running for a while
+ * and there have been stacks all over and these page tables
+ * are fully populated, there will be no further acquisitions of
+ * this lock.
+ */
+static DEFINE_SPINLOCK(shadow_table_allocation_lock);
+
+/*
+ * Returns -1 on error.
+ */
+static inline unsigned long get_pa_from_mapping(unsigned long vaddr)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+
+ pgd = pgd_offset_k(vaddr);
+ /*
+ * We made all the kernel PGDs present in kaiser_init().
+ * We expect them to stay that way.
+ */
+ BUG_ON(pgd_none(*pgd));
+ /*
+ * PGDs are either 512GB or 128TB on all x86_64
+ * configurations. We don't handle these.
+ */
+ BUG_ON(pgd_large(*pgd));
+
+ pud = pud_offset(pgd, vaddr);
+ if (pud_none(*pud)) {
+ WARN_ON_ONCE(1);
+ return -1;
+ }
+
+ if (pud_large(*pud))
+ return (pud_pfn(*pud) << PAGE_SHIFT) | (vaddr & ~PUD_PAGE_MASK);
+
+ pmd = pmd_offset(pud, vaddr);
+ if (pmd_none(*pmd)) {
+ WARN_ON_ONCE(1);
+ return -1;
+ }
+
+ if (pmd_large(*pmd))
+ return (pmd_pfn(*pmd) << PAGE_SHIFT) | (vaddr & ~PMD_PAGE_MASK);
+
+ pte = pte_offset_kernel(pmd, vaddr);
+ if (pte_none(*pte)) {
+ WARN_ON_ONCE(1);
+ return -1;
+ }
+
+ return (pte_pfn(*pte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK);
+}
+
+/*
+ * This is a relatively normal page table walk, except that it
+ * also tries to allocate page tables pages along the way.
+ *
+ * Returns a pointer to a PTE on success, or NULL on failure.
+ */
+static pte_t *kaiser_pagetable_walk(unsigned long address, bool user)
+{
+ pmd_t *pmd;
+ pud_t *pud;
+ pgd_t *pgd = native_get_shadow_pgd(pgd_offset_k(address));
+ gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
+ unsigned long prot = _KERNPG_TABLE;
+
+ if (pgd_none(*pgd)) {
+ WARN_ONCE(1, "All shadow pgds should have been populated");
+ return NULL;
+ }
+ BUILD_BUG_ON(pgd_large(*pgd) != 0);
+
+ if (user) {
+ /*
+ * The vsyscall page is the only page that will have
+ * _PAGE_USER set. Catch everything else.
+ */
+ BUG_ON(address != VSYSCALL_ADDR);
+
+ set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
+ prot = _PAGE_TABLE;
+ }
+
+ pud = pud_offset(pgd, address);
+ /* The shadow 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 (!new_pmd_page)
+ return NULL;
+ spin_lock(&shadow_table_allocation_lock);
+ if (pud_none(*pud)) {
+ set_pud(pud, __pud(prot | __pa(new_pmd_page)));
+ __inc_zone_page_state(virt_to_page((void *)
+ new_pmd_page), NR_KAISERTABLE);
+ } else
+ free_page(new_pmd_page);
+ spin_unlock(&shadow_table_allocation_lock);
+ }
+
+ pmd = pmd_offset(pud, address);
+ /* The shadow page tables do not use large mappings: */
+ 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;
+ spin_lock(&shadow_table_allocation_lock);
+ if (pmd_none(*pmd)) {
+ set_pmd(pmd, __pmd(prot | __pa(new_pte_page)));
+ __inc_zone_page_state(virt_to_page((void *)
+ new_pte_page), NR_KAISERTABLE);
+ } else
+ free_page(new_pte_page);
+ spin_unlock(&shadow_table_allocation_lock);
+ }
+
+ return pte_offset_kernel(pmd, address);
+}
+
+static int kaiser_add_user_map(const void *__start_addr, unsigned long size,
+ unsigned long flags)
+{
+ int ret = 0;
+ pte_t *pte;
+ unsigned long start_addr = (unsigned long )__start_addr;
+ unsigned long address = start_addr & PAGE_MASK;
+ unsigned long end_addr = PAGE_ALIGN(start_addr + size);
+ unsigned long target_address;
+
+ /*
+ * It is convenient for callers to pass in __PAGE_KERNEL etc,
+ * and there is no actual harm from setting _PAGE_GLOBAL, so
+ * long as CR4.PGE is not set. But it is nonetheless troubling
+ * to see Kaiser itself setting _PAGE_GLOBAL (now that "nokaiser"
+ * requires that not to be #defined to 0): so mask it off here.
+ */
+ flags &= ~_PAGE_GLOBAL;
+ if (!(__supported_pte_mask & _PAGE_NX))
+ flags &= ~_PAGE_NX;
+
+ for (; address < end_addr; address += PAGE_SIZE) {
+ target_address = get_pa_from_mapping(address);
+ if (target_address == -1) {
+ ret = -EIO;
+ break;
+ }
+ pte = kaiser_pagetable_walk(address, flags & _PAGE_USER);
+ if (!pte) {
+ ret = -ENOMEM;
+ break;
+ }
+ if (pte_none(*pte)) {
+ set_pte(pte, __pte(flags | target_address));
+ } else {
+ pte_t tmp;
+ set_pte(&tmp, __pte(flags | target_address));
+ WARN_ON_ONCE(!pte_same(*pte, tmp));
+ }
+ }
+ return ret;
+}
+
+static int kaiser_add_user_map_ptrs(const void *start, const void *end, unsigned long flags)
+{
+ unsigned long size = end - start;
+
+ return kaiser_add_user_map(start, size, flags);
+}
+
+/*
+ * Ensure that the top level of the (shadow) page tables are
+ * entirely populated. This ensures that all processes that get
+ * forked have the same entries. This way, we do not have to
+ * ever go set up new entries in older processes.
+ *
+ * Note: we never free these, so there are no updates to them
+ * after this.
+ */
+static void __init kaiser_init_all_pgds(void)
+{
+ pgd_t *pgd;
+ int i = 0;
+
+ pgd = native_get_shadow_pgd(pgd_offset_k((unsigned long )0));
+ for (i = PTRS_PER_PGD / 2; i < PTRS_PER_PGD; i++) {
+ pgd_t new_pgd;
+ pud_t *pud = pud_alloc_one(&init_mm,
+ PAGE_OFFSET + i * PGDIR_SIZE);
+ if (!pud) {
+ WARN_ON(1);
+ break;
+ }
+ inc_zone_page_state(virt_to_page(pud), NR_KAISERTABLE);
+ new_pgd = __pgd(_KERNPG_TABLE |__pa(pud));
+ /*
+ * Make sure not to stomp on some other pgd entry.
+ */
+ if (!pgd_none(pgd[i])) {
+ WARN_ON(1);
+ continue;
+ }
+ set_pgd(pgd + i, new_pgd);
+ }
+}
+
+#define kaiser_add_user_map_early(start, size, flags) do { \
+ int __ret = kaiser_add_user_map(start, size, flags); \
+ WARN_ON(__ret); \
+} while (0)
+
+#define kaiser_add_user_map_ptrs_early(start, end, flags) do { \
+ int __ret = kaiser_add_user_map_ptrs(start, end, flags); \
+ WARN_ON(__ret); \
+} while (0)
+
+void __init kaiser_check_boottime_disable(void)
+{
+ bool enable = true;
+ char arg[5];
+ int ret;
+
+ if (boot_cpu_has(X86_FEATURE_XENPV))
+ goto silent_disable;
+
+ ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
+ if (ret > 0) {
+ if (!strncmp(arg, "on", 2))
+ goto enable;
+
+ if (!strncmp(arg, "off", 3))
+ goto disable;
+
+ if (!strncmp(arg, "auto", 4))
+ goto skip;
+ }
+
+ if (cmdline_find_option_bool(boot_command_line, "nopti"))
+ goto disable;
+
+skip:
+ if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+ goto disable;
+
+enable:
+ if (enable)
+ setup_force_cpu_cap(X86_FEATURE_KAISER);
+
+ return;
+
+disable:
+ pr_info("disabled\n");
+
+silent_disable:
+ kaiser_enabled = 0;
+ setup_clear_cpu_cap(X86_FEATURE_KAISER);
+}
+
+/*
+ * If anything in here fails, we will likely die on one of the
+ * first kernel->user transitions and init will die. But, we
+ * will have most of the kernel up by then and should be able to
+ * get a clean warning out of it. If we BUG_ON() here, we run
+ * the risk of being before we have good console output.
+ */
+void __init kaiser_init(void)
+{
+ int cpu;
+
+ if (!kaiser_enabled)
+ return;
+
+ kaiser_init_all_pgds();
+
+ /*
+ * Note that this sets _PAGE_USER and it needs to happen when the
+ * pagetable hierarchy gets created, i.e., early. Otherwise
+ * kaiser_pagetable_walk() will encounter initialized PTEs in the
+ * hierarchy and not set the proper permissions, leading to the
+ * pagefaults with page-protection violations when trying to read the
+ * vsyscall page. For example.
+ */
+ if (vsyscall_enabled())
+ kaiser_add_user_map_early((void *)VSYSCALL_ADDR,
+ PAGE_SIZE,
+ vsyscall_pgprot);
+
+ for_each_possible_cpu(cpu) {
+ void *percpu_vaddr = __per_cpu_user_mapped_start +
+ per_cpu_offset(cpu);
+ unsigned long percpu_sz = __per_cpu_user_mapped_end -
+ __per_cpu_user_mapped_start;
+ kaiser_add_user_map_early(percpu_vaddr, percpu_sz,
+ __PAGE_KERNEL);
+ }
+
+ /*
+ * Map the entry/exit text section, which is needed at
+ * switches from user to and from kernel.
+ */
+ kaiser_add_user_map_ptrs_early(__entry_text_start, __entry_text_end,
+ __PAGE_KERNEL_RX);
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ kaiser_add_user_map_ptrs_early(__irqentry_text_start,
+ __irqentry_text_end,
+ __PAGE_KERNEL_RX);
+#endif
+ kaiser_add_user_map_early((void *)idt_descr.address,
+ sizeof(gate_desc) * NR_VECTORS,
+ __PAGE_KERNEL_RO);
+#ifdef CONFIG_TRACING
+ kaiser_add_user_map_early(&trace_idt_descr,
+ sizeof(trace_idt_descr),
+ __PAGE_KERNEL);
+ kaiser_add_user_map_early(&trace_idt_table,
+ sizeof(gate_desc) * NR_VECTORS,
+ __PAGE_KERNEL);
+#endif
+ kaiser_add_user_map_early(&debug_idt_descr, sizeof(debug_idt_descr),
+ __PAGE_KERNEL);
+ kaiser_add_user_map_early(&debug_idt_table,
+ sizeof(gate_desc) * NR_VECTORS,
+ __PAGE_KERNEL);
+
+ pr_info("enabled\n");
+}
+
+/* Add a mapping to the shadow mapping, and synchronize the mappings */
+int kaiser_add_mapping(unsigned long addr, unsigned long size, unsigned long flags)
+{
+ if (!kaiser_enabled)
+ return 0;
+ return kaiser_add_user_map((const void *)addr, size, flags);
+}
+
+void kaiser_remove_mapping(unsigned long start, unsigned long size)
+{
+ extern void unmap_pud_range_nofree(pgd_t *pgd,
+ unsigned long start, unsigned long end);
+ unsigned long end = start + size;
+ unsigned long addr, next;
+ pgd_t *pgd;
+
+ if (!kaiser_enabled)
+ return;
+ pgd = native_get_shadow_pgd(pgd_offset_k(start));
+ for (addr = start; addr < end; pgd++, addr = next) {
+ next = pgd_addr_end(addr, end);
+ unmap_pud_range_nofree(pgd, addr, next);
+ }
+}
+
+/*
+ * Page table pages are page-aligned. The lower half of the top
+ * level is used for userspace and the top half for the kernel.
+ * This returns true for user pages that need to get copied into
+ * both the user and kernel copies of the page tables, and false
+ * for kernel pages that should only be in the kernel copy.
+ */
+static inline bool is_userspace_pgd(pgd_t *pgdp)
+{
+ return ((unsigned long)pgdp % PAGE_SIZE) < (PAGE_SIZE / 2);
+}
+
+pgd_t kaiser_set_shadow_pgd(pgd_t *pgdp, pgd_t pgd)
+{
+ if (!kaiser_enabled)
+ return pgd;
+ /*
+ * Do we need to also populate the shadow pgd? Check _PAGE_USER to
+ * skip cases like kexec and EFI which make temporary low mappings.
+ */
+ if (pgd.pgd & _PAGE_USER) {
+ if (is_userspace_pgd(pgdp)) {
+ native_get_shadow_pgd(pgdp)->pgd = pgd.pgd;
+ /*
+ * Even if the entry is *mapping* userspace, ensure
+ * that userspace can not use it. This way, if we
+ * get out to userspace running on the kernel CR3,
+ * userspace will crash instead of running.
+ */
+ if (__supported_pte_mask & _PAGE_NX)
+ pgd.pgd |= _PAGE_NX;
+ }
+ } else if (!pgd.pgd) {
+ /*
+ * pgd_clear() cannot check _PAGE_USER, and is even used to
+ * clear corrupted pgd entries: so just rely on cases like
+ * kexec and EFI never to be using pgd_clear().
+ */
+ if (!WARN_ON_ONCE((unsigned long)pgdp & PAGE_SIZE) &&
+ is_userspace_pgd(pgdp))
+ native_get_shadow_pgd(pgdp)->pgd = pgd.pgd;
+ }
+ return pgd;
+}
+
+void kaiser_setup_pcid(void)
+{
+ unsigned long user_cr3 = KAISER_SHADOW_PGD_OFFSET;
+
+ if (this_cpu_has(X86_FEATURE_PCID))
+ user_cr3 |= X86_CR3_PCID_USER_NOFLUSH;
+ /*
+ * These variables are used by the entry/exit
+ * code to change PCID and pgd and TLB flushing.
+ */
+ this_cpu_write(x86_cr3_pcid_user, user_cr3);
+}
+
+/*
+ * Make a note that this cpu will need to flush USER tlb on return to user.
+ * If cpu does not have PCID, then the NOFLUSH bit will never have been set.
+ */
+void kaiser_flush_tlb_on_return_to_user(void)
+{
+ if (this_cpu_has(X86_FEATURE_PCID))
+ this_cpu_write(x86_cr3_pcid_user,
+ X86_CR3_PCID_USER_FLUSH | KAISER_SHADOW_PGD_OFFSET);
+}
+EXPORT_SYMBOL(kaiser_flush_tlb_on_return_to_user);
generated by cgit v1.2.3 (git 2.0.4) at 2024-04-27 01:39:44 +0000