--- /dev/null
+/*
+ * mpx.c - Memory Protection eXtensions
+ *
+ * Copyright (c) 2014, Intel Corporation.
+ * Qiaowei Ren <qiaowei.ren@intel.com>
+ * Dave Hansen <dave.hansen@intel.com>
+ */
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/sched/sysctl.h>
+
+#include <asm/i387.h>
+#include <asm/insn.h>
+#include <asm/mman.h>
+#include <asm/mmu_context.h>
+#include <asm/mpx.h>
+#include <asm/processor.h>
+#include <asm/fpu-internal.h>
+
+static const char *mpx_mapping_name(struct vm_area_struct *vma)
+{
+ return "[mpx]";
+}
+
+static struct vm_operations_struct mpx_vma_ops = {
+ .name = mpx_mapping_name,
+};
+
+static int is_mpx_vma(struct vm_area_struct *vma)
+{
+ return (vma->vm_ops == &mpx_vma_ops);
+}
+
+/*
+ * This is really a simplified "vm_mmap". it only handles MPX
+ * bounds tables (the bounds directory is user-allocated).
+ *
+ * Later on, we use the vma->vm_ops to uniquely identify these
+ * VMAs.
+ */
+static unsigned long mpx_mmap(unsigned long len)
+{
+ unsigned long ret;
+ unsigned long addr, pgoff;
+ struct mm_struct *mm = current->mm;
+ vm_flags_t vm_flags;
+ struct vm_area_struct *vma;
+
+ /* Only bounds table and bounds directory can be allocated here */
+ if (len != MPX_BD_SIZE_BYTES && len != MPX_BT_SIZE_BYTES)
+ return -EINVAL;
+
+ down_write(&mm->mmap_sem);
+
+ /* Too many mappings? */
+ if (mm->map_count > sysctl_max_map_count) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ /* Obtain the address to map to. we verify (or select) it and ensure
+ * that it represents a valid section of the address space.
+ */
+ addr = get_unmapped_area(NULL, 0, len, 0, MAP_ANONYMOUS | MAP_PRIVATE);
+ if (addr & ~PAGE_MASK) {
+ ret = addr;
+ goto out;
+ }
+
+ vm_flags = VM_READ | VM_WRITE | VM_MPX |
+ mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+
+ /* Set pgoff according to addr for anon_vma */
+ pgoff = addr >> PAGE_SHIFT;
+
+ ret = mmap_region(NULL, addr, len, vm_flags, pgoff);
+ if (IS_ERR_VALUE(ret))
+ goto out;
+
+ vma = find_vma(mm, ret);
+ if (!vma) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ vma->vm_ops = &mpx_vma_ops;
+
+ if (vm_flags & VM_LOCKED) {
+ up_write(&mm->mmap_sem);
+ mm_populate(ret, len);
+ return ret;
+ }
+
+out:
+ up_write(&mm->mmap_sem);
+ return ret;
+}
+
+enum reg_type {
+ REG_TYPE_RM = 0,
+ REG_TYPE_INDEX,
+ REG_TYPE_BASE,
+};
+
+static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
+ enum reg_type type)
+{
+ int regno = 0;
+
+ static const int regoff[] = {
+ offsetof(struct pt_regs, ax),
+ offsetof(struct pt_regs, cx),
+ offsetof(struct pt_regs, dx),
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, sp),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+#ifdef CONFIG_X86_64
+ offsetof(struct pt_regs, r8),
+ offsetof(struct pt_regs, r9),
+ offsetof(struct pt_regs, r10),
+ offsetof(struct pt_regs, r11),
+ offsetof(struct pt_regs, r12),
+ offsetof(struct pt_regs, r13),
+ offsetof(struct pt_regs, r14),
+ offsetof(struct pt_regs, r15),
+#endif
+ };
+ int nr_registers = ARRAY_SIZE(regoff);
+ /*
+ * Don't possibly decode a 32-bit instructions as
+ * reading a 64-bit-only register.
+ */
+ if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
+ nr_registers -= 8;
+
+ switch (type) {
+ case REG_TYPE_RM:
+ regno = X86_MODRM_RM(insn->modrm.value);
+ if (X86_REX_B(insn->rex_prefix.value) == 1)
+ regno += 8;
+ break;
+
+ case REG_TYPE_INDEX:
+ regno = X86_SIB_INDEX(insn->sib.value);
+ if (X86_REX_X(insn->rex_prefix.value) == 1)
+ regno += 8;
+ break;
+
+ case REG_TYPE_BASE:
+ regno = X86_SIB_BASE(insn->sib.value);
+ if (X86_REX_B(insn->rex_prefix.value) == 1)
+ regno += 8;
+ break;
+
+ default:
+ pr_err("invalid register type");
+ BUG();
+ break;
+ }
+
+ if (regno > nr_registers) {
+ WARN_ONCE(1, "decoded an instruction with an invalid register");
+ return -EINVAL;
+ }
+ return regoff[regno];
+}
+
+/*
+ * return the address being referenced be instruction
+ * for rm=3 returning the content of the rm reg
+ * for rm!=3 calculates the address using SIB and Disp
+ */
+static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
+{
+ unsigned long addr, base, indx;
+ int addr_offset, base_offset, indx_offset;
+ insn_byte_t sib;
+
+ insn_get_modrm(insn);
+ insn_get_sib(insn);
+ sib = insn->sib.value;
+
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
+ if (addr_offset < 0)
+ goto out_err;
+ addr = regs_get_register(regs, addr_offset);
+ } else {
+ if (insn->sib.nbytes) {
+ base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
+ if (base_offset < 0)
+ goto out_err;
+
+ indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
+ if (indx_offset < 0)
+ goto out_err;
+
+ base = regs_get_register(regs, base_offset);
+ indx = regs_get_register(regs, indx_offset);
+ addr = base + indx * (1 << X86_SIB_SCALE(sib));
+ } else {
+ addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
+ if (addr_offset < 0)
+ goto out_err;
+ addr = regs_get_register(regs, addr_offset);
+ }
+ addr += insn->displacement.value;
+ }
+ return (void __user *)addr;
+out_err:
+ return (void __user *)-1;
+}
+
+static int mpx_insn_decode(struct insn *insn,
+ struct pt_regs *regs)
+{
+ unsigned char buf[MAX_INSN_SIZE];
+ int x86_64 = !test_thread_flag(TIF_IA32);
+ int not_copied;
+ int nr_copied;
+
+ not_copied = copy_from_user(buf, (void __user *)regs->ip, sizeof(buf));
+ nr_copied = sizeof(buf) - not_copied;
+ /*
+ * The decoder _should_ fail nicely if we pass it a short buffer.
+ * But, let's not depend on that implementation detail. If we
+ * did not get anything, just error out now.
+ */
+ if (!nr_copied)
+ return -EFAULT;
+ insn_init(insn, buf, nr_copied, x86_64);
+ insn_get_length(insn);
+ /*
+ * copy_from_user() tries to get as many bytes as we could see in
+ * the largest possible instruction. If the instruction we are
+ * after is shorter than that _and_ we attempt to copy from
+ * something unreadable, we might get a short read. This is OK
+ * as long as the read did not stop in the middle of the
+ * instruction. Check to see if we got a partial instruction.
+ */
+ if (nr_copied < insn->length)
+ return -EFAULT;
+
+ insn_get_opcode(insn);
+ /*
+ * We only _really_ need to decode bndcl/bndcn/bndcu
+ * Error out on anything else.
+ */
+ if (insn->opcode.bytes[0] != 0x0f)
+ goto bad_opcode;
+ if ((insn->opcode.bytes[1] != 0x1a) &&
+ (insn->opcode.bytes[1] != 0x1b))
+ goto bad_opcode;
+
+ return 0;
+bad_opcode:
+ return -EINVAL;
+}
+
+/*
+ * If a bounds overflow occurs then a #BR is generated. This
+ * function decodes MPX instructions to get violation address
+ * and set this address into extended struct siginfo.
+ *
+ * Note that this is not a super precise way of doing this.
+ * Userspace could have, by the time we get here, written
+ * anything it wants in to the instructions. We can not
+ * trust anything about it. They might not be valid
+ * instructions or might encode invalid registers, etc...
+ *
+ * The caller is expected to kfree() the returned siginfo_t.
+ */
+siginfo_t *mpx_generate_siginfo(struct pt_regs *regs,
+ struct xsave_struct *xsave_buf)
+{
+ struct bndreg *bndregs, *bndreg;
+ siginfo_t *info = NULL;
+ struct insn insn;
+ uint8_t bndregno;
+ int err;
+
+ err = mpx_insn_decode(&insn, regs);
+ if (err)
+ goto err_out;
+
+ /*
+ * We know at this point that we are only dealing with
+ * MPX instructions.
+ */
+ insn_get_modrm(&insn);
+ bndregno = X86_MODRM_REG(insn.modrm.value);
+ if (bndregno > 3) {
+ err = -EINVAL;
+ goto err_out;
+ }
+ /* get the bndregs _area_ of the xsave structure */
+ bndregs = get_xsave_addr(xsave_buf, XSTATE_BNDREGS);
+ if (!bndregs) {
+ err = -EINVAL;
+ goto err_out;
+ }
+ /* now go select the individual register in the set of 4 */
+ bndreg = &bndregs[bndregno];
+
+ info = kzalloc(sizeof(*info), GFP_KERNEL);
+ if (!info) {
+ err = -ENOMEM;
+ goto err_out;
+ }
+ /*
+ * The registers are always 64-bit, but the upper 32
+ * bits are ignored in 32-bit mode. Also, note that the
+ * upper bounds are architecturally represented in 1's
+ * complement form.
+ *
+ * The 'unsigned long' cast is because the compiler
+ * complains when casting from integers to different-size
+ * pointers.
+ */
+ info->si_lower = (void __user *)(unsigned long)bndreg->lower_bound;
+ info->si_upper = (void __user *)(unsigned long)~bndreg->upper_bound;
+ info->si_addr_lsb = 0;
+ info->si_signo = SIGSEGV;
+ info->si_errno = 0;
+ info->si_code = SEGV_BNDERR;
+ info->si_addr = mpx_get_addr_ref(&insn, regs);
+ /*
+ * We were not able to extract an address from the instruction,
+ * probably because there was something invalid in it.
+ */
+ if (info->si_addr == (void *)-1) {
+ err = -EINVAL;
+ goto err_out;
+ }
+ return info;
+err_out:
+ /* info might be NULL, but kfree() handles that */
+ kfree(info);
+ return ERR_PTR(err);
+}
+
+static __user void *task_get_bounds_dir(struct task_struct *tsk)
+{
+ struct bndcsr *bndcsr;
+
+ if (!cpu_feature_enabled(X86_FEATURE_MPX))
+ return MPX_INVALID_BOUNDS_DIR;
+
+ /*
+ * 32-bit binaries on 64-bit kernels are currently
+ * unsupported.
+ */
+ if (IS_ENABLED(CONFIG_X86_64) && test_thread_flag(TIF_IA32))
+ return MPX_INVALID_BOUNDS_DIR;
+ /*
+ * The bounds directory pointer is stored in a register
+ * only accessible if we first do an xsave.
+ */
+ fpu_save_init(&tsk->thread.fpu);
+ bndcsr = get_xsave_addr(&tsk->thread.fpu.state->xsave, XSTATE_BNDCSR);
+ if (!bndcsr)
+ return MPX_INVALID_BOUNDS_DIR;
+
+ /*
+ * Make sure the register looks valid by checking the
+ * enable bit.
+ */
+ if (!(bndcsr->bndcfgu & MPX_BNDCFG_ENABLE_FLAG))
+ return MPX_INVALID_BOUNDS_DIR;
+
+ /*
+ * Lastly, mask off the low bits used for configuration
+ * flags, and return the address of the bounds table.
+ */
+ return (void __user *)(unsigned long)
+ (bndcsr->bndcfgu & MPX_BNDCFG_ADDR_MASK);
+}
+
+int mpx_enable_management(struct task_struct *tsk)
+{
+ void __user *bd_base = MPX_INVALID_BOUNDS_DIR;
+ struct mm_struct *mm = tsk->mm;
+ int ret = 0;
+
+ /*
+ * runtime in the userspace will be responsible for allocation of
+ * the bounds directory. Then, it will save the base of the bounds
+ * directory into XSAVE/XRSTOR Save Area and enable MPX through
+ * XRSTOR instruction.
+ *
+ * fpu_xsave() is expected to be very expensive. Storing the bounds
+ * directory here means that we do not have to do xsave in the unmap
+ * path; we can just use mm->bd_addr instead.
+ */
+ bd_base = task_get_bounds_dir(tsk);
+ down_write(&mm->mmap_sem);
+ mm->bd_addr = bd_base;
+ if (mm->bd_addr == MPX_INVALID_BOUNDS_DIR)
+ ret = -ENXIO;
+
+ up_write(&mm->mmap_sem);
+ return ret;
+}
+
+int mpx_disable_management(struct task_struct *tsk)
+{
+ struct mm_struct *mm = current->mm;
+
+ if (!cpu_feature_enabled(X86_FEATURE_MPX))
+ return -ENXIO;
+
+ down_write(&mm->mmap_sem);
+ mm->bd_addr = MPX_INVALID_BOUNDS_DIR;
+ up_write(&mm->mmap_sem);
+ return 0;
+}
+
+/*
+ * With 32-bit mode, MPX_BT_SIZE_BYTES is 4MB, and the size of each
+ * bounds table is 16KB. With 64-bit mode, MPX_BT_SIZE_BYTES is 2GB,
+ * and the size of each bounds table is 4MB.
+ */
+static int allocate_bt(long __user *bd_entry)
+{
+ unsigned long expected_old_val = 0;
+ unsigned long actual_old_val = 0;
+ unsigned long bt_addr;
+ int ret = 0;
+
+ /*
+ * Carve the virtual space out of userspace for the new
+ * bounds table:
+ */
+ bt_addr = mpx_mmap(MPX_BT_SIZE_BYTES);
+ if (IS_ERR((void *)bt_addr))
+ return PTR_ERR((void *)bt_addr);
+ /*
+ * Set the valid flag (kinda like _PAGE_PRESENT in a pte)
+ */
+ bt_addr = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
+
+ /*
+ * Go poke the address of the new bounds table in to the
+ * bounds directory entry out in userspace memory. Note:
+ * we may race with another CPU instantiating the same table.
+ * In that case the cmpxchg will see an unexpected
+ * 'actual_old_val'.
+ *
+ * This can fault, but that's OK because we do not hold
+ * mmap_sem at this point, unlike some of the other part
+ * of the MPX code that have to pagefault_disable().
+ */
+ ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
+ expected_old_val, bt_addr);
+ if (ret)
+ goto out_unmap;
+
+ /*
+ * The user_atomic_cmpxchg_inatomic() will only return nonzero
+ * for faults, *not* if the cmpxchg itself fails. Now we must
+ * verify that the cmpxchg itself completed successfully.
+ */
+ /*
+ * We expected an empty 'expected_old_val', but instead found
+ * an apparently valid entry. Assume we raced with another
+ * thread to instantiate this table and desclare succecss.
+ */
+ if (actual_old_val & MPX_BD_ENTRY_VALID_FLAG) {
+ ret = 0;
+ goto out_unmap;
+ }
+ /*
+ * We found a non-empty bd_entry but it did not have the
+ * VALID_FLAG set. Return an error which will result in
+ * a SEGV since this probably means that somebody scribbled
+ * some invalid data in to a bounds table.
+ */
+ if (expected_old_val != actual_old_val) {
+ ret = -EINVAL;
+ goto out_unmap;
+ }
+ return 0;
+out_unmap:
+ vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);
+ return ret;
+}
+
+/*
+ * When a BNDSTX instruction attempts to save bounds to a bounds
+ * table, it will first attempt to look up the table in the
+ * first-level bounds directory. If it does not find a table in
+ * the directory, a #BR is generated and we get here in order to
+ * allocate a new table.
+ *
+ * With 32-bit mode, the size of BD is 4MB, and the size of each
+ * bound table is 16KB. With 64-bit mode, the size of BD is 2GB,
+ * and the size of each bound table is 4MB.
+ */
+static int do_mpx_bt_fault(struct xsave_struct *xsave_buf)
+{
+ unsigned long bd_entry, bd_base;
+ struct bndcsr *bndcsr;
+
+ bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);
+ if (!bndcsr)
+ return -EINVAL;
+ /*
+ * Mask off the preserve and enable bits
+ */
+ bd_base = bndcsr->bndcfgu & MPX_BNDCFG_ADDR_MASK;
+ /*
+ * The hardware provides the address of the missing or invalid
+ * entry via BNDSTATUS, so we don't have to go look it up.
+ */
+ bd_entry = bndcsr->bndstatus & MPX_BNDSTA_ADDR_MASK;
+ /*
+ * Make sure the directory entry is within where we think
+ * the directory is.
+ */
+ if ((bd_entry < bd_base) ||
+ (bd_entry >= bd_base + MPX_BD_SIZE_BYTES))
+ return -EINVAL;
+
+ return allocate_bt((long __user *)bd_entry);
+}
+
+int mpx_handle_bd_fault(struct xsave_struct *xsave_buf)
+{
+ /*
+ * Userspace never asked us to manage the bounds tables,
+ * so refuse to help.
+ */
+ if (!kernel_managing_mpx_tables(current->mm))
+ return -EINVAL;
+
+ if (do_mpx_bt_fault(xsave_buf)) {
+ force_sig(SIGSEGV, current);
+ /*
+ * The force_sig() is essentially "handling" this
+ * exception, so we do not pass up the error
+ * from do_mpx_bt_fault().
+ */
+ }
+ return 0;
+}
+
+/*
+ * A thin wrapper around get_user_pages(). Returns 0 if the
+ * fault was resolved or -errno if not.
+ */
+static int mpx_resolve_fault(long __user *addr, int write)
+{
+ long gup_ret;
+ int nr_pages = 1;
+ int force = 0;
+
+ gup_ret = get_user_pages(current, current->mm, (unsigned long)addr,
+ nr_pages, write, force, NULL, NULL);
+ /*
+ * get_user_pages() returns number of pages gotten.
+ * 0 means we failed to fault in and get anything,
+ * probably because 'addr' is bad.
+ */
+ if (!gup_ret)
+ return -EFAULT;
+ /* Other error, return it */
+ if (gup_ret < 0)
+ return gup_ret;
+ /* must have gup'd a page and gup_ret>0, success */
+ return 0;
+}
+
+/*
+ * Get the base of bounds tables pointed by specific bounds
+ * directory entry.
+ */
+static int get_bt_addr(struct mm_struct *mm,
+ long __user *bd_entry, unsigned long *bt_addr)
+{
+ int ret;
+ int valid_bit;
+
+ if (!access_ok(VERIFY_READ, (bd_entry), sizeof(*bd_entry)))
+ return -EFAULT;
+
+ while (1) {
+ int need_write = 0;
+
+ pagefault_disable();
+ ret = get_user(*bt_addr, bd_entry);
+ pagefault_enable();
+ if (!ret)
+ break;
+ if (ret == -EFAULT)
+ ret = mpx_resolve_fault(bd_entry, need_write);
+ /*
+ * If we could not resolve the fault, consider it
+ * userspace's fault and error out.
+ */
+ if (ret)
+ return ret;
+ }
+
+ valid_bit = *bt_addr & MPX_BD_ENTRY_VALID_FLAG;
+ *bt_addr &= MPX_BT_ADDR_MASK;
+
+ /*
+ * When the kernel is managing bounds tables, a bounds directory
+ * entry will either have a valid address (plus the valid bit)
+ * *OR* be completely empty. If we see a !valid entry *and* some
+ * data in the address field, we know something is wrong. This
+ * -EINVAL return will cause a SIGSEGV.
+ */
+ if (!valid_bit && *bt_addr)
+ return -EINVAL;
+ /*
+ * Do we have an completely zeroed bt entry? That is OK. It
+ * just means there was no bounds table for this memory. Make
+ * sure to distinguish this from -EINVAL, which will cause
+ * a SEGV.
+ */
+ if (!valid_bit)
+ return -ENOENT;
+
+ return 0;
+}
+
+/*
+ * Free the backing physical pages of bounds table 'bt_addr'.
+ * Assume start...end is within that bounds table.
+ */
+static int zap_bt_entries(struct mm_struct *mm,
+ unsigned long bt_addr,
+ unsigned long start, unsigned long end)
+{
+ struct vm_area_struct *vma;
+ unsigned long addr, len;
+
+ /*
+ * Find the first overlapping vma. If vma->vm_start > start, there
+ * will be a hole in the bounds table. This -EINVAL return will
+ * cause a SIGSEGV.
+ */
+ vma = find_vma(mm, start);
+ if (!vma || vma->vm_start > start)
+ return -EINVAL;
+
+ /*
+ * A NUMA policy on a VM_MPX VMA could cause this bouds table to
+ * be split. So we need to look across the entire 'start -> end'
+ * range of this bounds table, find all of the VM_MPX VMAs, and
+ * zap only those.
+ */
+ addr = start;
+ while (vma && vma->vm_start < end) {
+ /*
+ * We followed a bounds directory entry down
+ * here. If we find a non-MPX VMA, that's bad,
+ * so stop immediately and return an error. This
+ * probably results in a SIGSEGV.
+ */
+ if (!is_mpx_vma(vma))
+ return -EINVAL;
+
+ len = min(vma->vm_end, end) - addr;
+ zap_page_range(vma, addr, len, NULL);
+
+ vma = vma->vm_next;
+ addr = vma->vm_start;
+ }
+
+ return 0;
+}
+
+static int unmap_single_bt(struct mm_struct *mm,
+ long __user *bd_entry, unsigned long bt_addr)
+{
+ unsigned long expected_old_val = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
+ unsigned long actual_old_val = 0;
+ int ret;
+
+ while (1) {
+ int need_write = 1;
+
+ pagefault_disable();
+ ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
+ expected_old_val, 0);
+ pagefault_enable();
+ if (!ret)
+ break;
+ if (ret == -EFAULT)
+ ret = mpx_resolve_fault(bd_entry, need_write);
+ /*
+ * If we could not resolve the fault, consider it
+ * userspace's fault and error out.
+ */
+ if (ret)
+ return ret;
+ }
+ /*
+ * The cmpxchg was performed, check the results.
+ */
+ if (actual_old_val != expected_old_val) {
+ /*
+ * Someone else raced with us to unmap the table.
+ * There was no bounds table pointed to by the
+ * directory, so declare success. Somebody freed
+ * it.
+ */
+ if (!actual_old_val)
+ return 0;
+ /*
+ * Something messed with the bounds directory
+ * entry. We hold mmap_sem for read or write
+ * here, so it could not be a _new_ bounds table
+ * that someone just allocated. Something is
+ * wrong, so pass up the error and SIGSEGV.
+ */
+ return -EINVAL;
+ }
+
+ /*
+ * Note, we are likely being called under do_munmap() already. To
+ * avoid recursion, do_munmap() will check whether it comes
+ * from one bounds table through VM_MPX flag.
+ */
+ return do_munmap(mm, bt_addr, MPX_BT_SIZE_BYTES);
+}
+
+/*
+ * If the bounds table pointed by bounds directory 'bd_entry' is
+ * not shared, unmap this whole bounds table. Otherwise, only free
+ * those backing physical pages of bounds table entries covered
+ * in this virtual address region start...end.
+ */
+static int unmap_shared_bt(struct mm_struct *mm,
+ long __user *bd_entry, unsigned long start,
+ unsigned long end, bool prev_shared, bool next_shared)
+{
+ unsigned long bt_addr;
+ int ret;
+
+ ret = get_bt_addr(mm, bd_entry, &bt_addr);
+ /*
+ * We could see an "error" ret for not-present bounds
+ * tables (not really an error), or actual errors, but
+ * stop unmapping either way.
+ */
+ if (ret)
+ return ret;
+
+ if (prev_shared && next_shared)
+ ret = zap_bt_entries(mm, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(end));
+ else if (prev_shared)
+ ret = zap_bt_entries(mm, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
+ bt_addr+MPX_BT_SIZE_BYTES);
+ else if (next_shared)
+ ret = zap_bt_entries(mm, bt_addr, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(end));
+ else
+ ret = unmap_single_bt(mm, bd_entry, bt_addr);
+
+ return ret;
+}
+
+/*
+ * A virtual address region being munmap()ed might share bounds table
+ * with adjacent VMAs. We only need to free the backing physical
+ * memory of these shared bounds tables entries covered in this virtual
+ * address region.
+ */
+static int unmap_edge_bts(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ int ret;
+ long __user *bde_start, *bde_end;
+ struct vm_area_struct *prev, *next;
+ bool prev_shared = false, next_shared = false;
+
+ bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
+ bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+
+ /*
+ * Check whether bde_start and bde_end are shared with adjacent
+ * VMAs.
+ *
+ * We already unliked the VMAs from the mm's rbtree so 'start'
+ * is guaranteed to be in a hole. This gets us the first VMA
+ * before the hole in to 'prev' and the next VMA after the hole
+ * in to 'next'.
+ */
+ next = find_vma_prev(mm, start, &prev);
+ if (prev && (mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(prev->vm_end-1))
+ == bde_start)
+ prev_shared = true;
+ if (next && (mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(next->vm_start))
+ == bde_end)
+ next_shared = true;
+
+ /*
+ * This virtual address region being munmap()ed is only
+ * covered by one bounds table.
+ *
+ * In this case, if this table is also shared with adjacent
+ * VMAs, only part of the backing physical memory of the bounds
+ * table need be freeed. Otherwise the whole bounds table need
+ * be unmapped.
+ */
+ if (bde_start == bde_end) {
+ return unmap_shared_bt(mm, bde_start, start, end,
+ prev_shared, next_shared);
+ }
+
+ /*
+ * If more than one bounds tables are covered in this virtual
+ * address region being munmap()ed, we need to separately check
+ * whether bde_start and bde_end are shared with adjacent VMAs.
+ */
+ ret = unmap_shared_bt(mm, bde_start, start, end, prev_shared, false);
+ if (ret)
+ return ret;
+ ret = unmap_shared_bt(mm, bde_end, start, end, false, next_shared);
+ if (ret)
+ return ret;
+
+ return 0;
+}
+
+static int mpx_unmap_tables(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ int ret;
+ long __user *bd_entry, *bde_start, *bde_end;
+ unsigned long bt_addr;
+
+ /*
+ * "Edge" bounds tables are those which are being used by the region
+ * (start -> end), but that may be shared with adjacent areas. If they
+ * turn out to be completely unshared, they will be freed. If they are
+ * shared, we will free the backing store (like an MADV_DONTNEED) for
+ * areas used by this region.
+ */
+ ret = unmap_edge_bts(mm, start, end);
+ switch (ret) {
+ /* non-present tables are OK */
+ case 0:
+ case -ENOENT:
+ /* Success, or no tables to unmap */
+ break;
+ case -EINVAL:
+ case -EFAULT:
+ default:
+ return ret;
+ }
+
+ /*
+ * Only unmap the bounds table that are
+ * 1. fully covered
+ * 2. not at the edges of the mapping, even if full aligned
+ */
+ bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
+ bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+ for (bd_entry = bde_start + 1; bd_entry < bde_end; bd_entry++) {
+ ret = get_bt_addr(mm, bd_entry, &bt_addr);
+ switch (ret) {
+ case 0:
+ break;
+ case -ENOENT:
+ /* No table here, try the next one */
+ continue;
+ case -EINVAL:
+ case -EFAULT:
+ default:
+ /*
+ * Note: we are being strict here.
+ * Any time we run in to an issue
+ * unmapping tables, we stop and
+ * SIGSEGV.
+ */
+ return ret;
+ }
+
+ ret = unmap_single_bt(mm, bd_entry, bt_addr);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
+/*
+ * Free unused bounds tables covered in a virtual address region being
+ * munmap()ed. Assume end > start.
+ *
+ * This function will be called by do_munmap(), and the VMAs covering
+ * the virtual address region start...end have already been split if
+ * necessary, and the 'vma' is the first vma in this range (start -> end).
+ */
+void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+ int ret;
+
+ /*
+ * Refuse to do anything unless userspace has asked
+ * the kernel to help manage the bounds tables,
+ */
+ if (!kernel_managing_mpx_tables(current->mm))
+ return;
+ /*
+ * This will look across the entire 'start -> end' range,
+ * and find all of the non-VM_MPX VMAs.
+ *
+ * To avoid recursion, if a VM_MPX vma is found in the range
+ * (start->end), we will not continue follow-up work. This
+ * recursion represents having bounds tables for bounds tables,
+ * which should not occur normally. Being strict about it here
+ * helps ensure that we do not have an exploitable stack overflow.
+ */
+ do {
+ if (vma->vm_flags & VM_MPX)
+ return;
+ vma = vma->vm_next;
+ } while (vma && vma->vm_start < end);
+
+ ret = mpx_unmap_tables(mm, start, end);
+ if (ret)
+ force_sig(SIGSEGV, current);
+}
Code Review / kvmfornfv.git / blobdiff