diff options
Diffstat (limited to 'arch/x86/mm/mpx.c')
| -rw-r--r-- | arch/x86/mm/mpx.c | 928 |
1 files changed, 928 insertions, 0 deletions
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c new file mode 100644 index 000000000000..67ebf5751222 --- /dev/null +++ b/arch/x86/mm/mpx.c @@ -0,0 +1,928 @@ +/* + * 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; + + /* + * 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); +} |