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|
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
* Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
* Copyright (C) 2002 Andi Kleen
*
* This handles calls from both 32bit and 64bit mode.
*
* Lock order:
* contex.ldt_usr_sem
* mmap_sem
* context.lock
*/
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <asm/ldt.h>
#include <asm/tlb.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
#include <asm/syscalls.h>
#include <asm/pgtable_areas.h>
/* This is a multiple of PAGE_SIZE. */
#define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
static inline void *ldt_slot_va(int slot)
{
return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
}
void load_mm_ldt(struct mm_struct *mm)
{
struct ldt_struct *ldt;
/* READ_ONCE synchronizes with smp_store_release */
ldt = READ_ONCE(mm->context.ldt);
/*
* Any change to mm->context.ldt is followed by an IPI to all
* CPUs with the mm active. The LDT will not be freed until
* after the IPI is handled by all such CPUs. This means that,
* if the ldt_struct changes before we return, the values we see
* will be safe, and the new values will be loaded before we run
* any user code.
*
* NB: don't try to convert this to use RCU without extreme care.
* We would still need IRQs off, because we don't want to change
* the local LDT after an IPI loaded a newer value than the one
* that we can see.
*/
if (unlikely(ldt)) {
if (static_cpu_has(X86_FEATURE_PTI)) {
if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
/*
* Whoops -- either the new LDT isn't mapped
* (if slot == -1) or is mapped into a bogus
* slot (if slot > 1).
*/
clear_LDT();
return;
}
/*
* If page table isolation is enabled, ldt->entries
* will not be mapped in the userspace pagetables.
* Tell the CPU to access the LDT through the alias
* at ldt_slot_va(ldt->slot).
*/
set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
} else {
set_ldt(ldt->entries, ldt->nr_entries);
}
} else {
clear_LDT();
}
}
void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
{
/*
* Load the LDT if either the old or new mm had an LDT.
*
* An mm will never go from having an LDT to not having an LDT. Two
* mms never share an LDT, so we don't gain anything by checking to
* see whether the LDT changed. There's also no guarantee that
* prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
* then prev->context.ldt will also be non-NULL.
*
* If we really cared, we could optimize the case where prev == next
* and we're exiting lazy mode. Most of the time, if this happens,
* we don't actually need to reload LDTR, but modify_ldt() is mostly
* used by legacy code and emulators where we don't need this level of
* performance.
*
* This uses | instead of || because it generates better code.
*/
if (unlikely((unsigned long)prev->context.ldt |
(unsigned long)next->context.ldt))
load_mm_ldt(next);
DEBUG_LOCKS_WARN_ON(preemptible());
}
static void refresh_ldt_segments(void)
{
#ifdef CONFIG_X86_64
unsigned short sel;
/*
* Make sure that the cached DS and ES descriptors match the updated
* LDT.
*/
savesegment(ds, sel);
if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
loadsegment(ds, sel);
savesegment(es, sel);
if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
loadsegment(es, sel);
#endif
}
/* context.lock is held by the task which issued the smp function call */
static void flush_ldt(void *__mm)
{
struct mm_struct *mm = __mm;
if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
return;
load_mm_ldt(mm);
refresh_ldt_segments();
}
/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
{
struct ldt_struct *new_ldt;
unsigned int alloc_size;
if (num_entries > LDT_ENTRIES)
return NULL;
new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
if (!new_ldt)
return NULL;
BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
alloc_size = num_entries * LDT_ENTRY_SIZE;
/*
* Xen is very picky: it requires a page-aligned LDT that has no
* trailing nonzero bytes in any page that contains LDT descriptors.
* Keep it simple: zero the whole allocation and never allocate less
* than PAGE_SIZE.
*/
if (alloc_size > PAGE_SIZE)
new_ldt->entries = vzalloc(alloc_size);
else
new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
if (!new_ldt->entries) {
kfree(new_ldt);
return NULL;
}
/* The new LDT isn't aliased for PTI yet. */
new_ldt->slot = -1;
new_ldt->nr_entries = num_entries;
return new_ldt;
}
#ifdef CONFIG_PAGE_TABLE_ISOLATION
static void do_sanity_check(struct mm_struct *mm,
bool had_kernel_mapping,
bool had_user_mapping)
{
if (mm->context.ldt) {
/*
* We already had an LDT. The top-level entry should already
* have been allocated and synchronized with the usermode
* tables.
*/
WARN_ON(!had_kernel_mapping);
if (boot_cpu_has(X86_FEATURE_PTI))
WARN_ON(!had_user_mapping);
} else {
/*
* This is the first time we're mapping an LDT for this process.
* Sync the pgd to the usermode tables.
*/
WARN_ON(had_kernel_mapping);
if (boot_cpu_has(X86_FEATURE_PTI))
WARN_ON(had_user_mapping);
}
}
#ifdef CONFIG_X86_PAE
static pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va)
{
p4d_t *p4d;
pud_t *pud;
if (pgd->pgd == 0)
return NULL;
p4d = p4d_offset(pgd, va);
if (p4d_none(*p4d))
return NULL;
pud = pud_offset(p4d, va);
if (pud_none(*pud))
return NULL;
return pmd_offset(pud, va);
}
static void map_ldt_struct_to_user(struct mm_struct *mm)
{
pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
pmd_t *k_pmd, *u_pmd;
k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
set_pmd(u_pmd, *k_pmd);
}
static void sanity_check_ldt_mapping(struct mm_struct *mm)
{
pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
bool had_kernel, had_user;
pmd_t *k_pmd, *u_pmd;
k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
had_kernel = (k_pmd->pmd != 0);
had_user = (u_pmd->pmd != 0);
do_sanity_check(mm, had_kernel, had_user);
}
#else /* !CONFIG_X86_PAE */
static void map_ldt_struct_to_user(struct mm_struct *mm)
{
pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
set_pgd(kernel_to_user_pgdp(pgd), *pgd);
}
static void sanity_check_ldt_mapping(struct mm_struct *mm)
{
pgd_t
|