diff options
Diffstat (limited to 'arch/x86/mm/mpx.c')
| -rw-r--r-- | arch/x86/mm/mpx.c | 948 |
1 files changed, 948 insertions, 0 deletions
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c new file mode 100644 index 000000000..e500949ba --- /dev/null +++ b/arch/x86/mm/mpx.c @@ -0,0 +1,948 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * 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/mm_types.h> +#include <linux/syscalls.h> +#include <linux/sched/sysctl.h> + +#include <asm/insn.h> +#include <asm/insn-eval.h> +#include <asm/mman.h> +#include <asm/mmu_context.h> +#include <asm/mpx.h> +#include <asm/processor.h> +#include <asm/fpu/internal.h> + +#define CREATE_TRACE_POINTS +#include <asm/trace/mpx.h> + +static inline unsigned long mpx_bd_size_bytes(struct mm_struct *mm) +{ + if (is_64bit_mm(mm)) + return MPX_BD_SIZE_BYTES_64; + else + return MPX_BD_SIZE_BYTES_32; +} + +static inline unsigned long mpx_bt_size_bytes(struct mm_struct *mm) +{ + if (is_64bit_mm(mm)) + return MPX_BT_SIZE_BYTES_64; + else + return MPX_BT_SIZE_BYTES_32; +} + +/* + * This is really a simplified "vm_mmap". it only handles MPX + * bounds tables (the bounds directory is user-allocated). + */ +static unsigned long mpx_mmap(unsigned long len) +{ + struct mm_struct *mm = current->mm; + unsigned long addr, populate; + + /* Only bounds table can be allocated here */ + if (len != mpx_bt_size_bytes(mm)) + return -EINVAL; + + down_write(&mm->mmap_sem); + addr = do_mmap(NULL, 0, len, PROT_READ | PROT_WRITE, + MAP_ANONYMOUS | MAP_PRIVATE, VM_MPX, 0, &populate, NULL); + up_write(&mm->mmap_sem); + if (populate) + mm_populate(addr, populate); + + return addr; +} + +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) +{ + const struct mpx_bndreg_state *bndregs; + const struct mpx_bndreg *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 bndregs field from current task's xsave area */ + bndregs = get_xsave_field_ptr(XFEATURE_MASK_BNDREGS); + if (!bndregs) { + err = -EINVAL; + goto err_out; + } + /* now go select the individual register in the set of 4 */ + bndreg = &bndregs->bndreg[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 = insn_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 __user *)-1) { + err = -EINVAL; + goto err_out; + } + trace_mpx_bounds_register_exception(info->si_addr, bndreg); + return info; +err_out: + /* info might be NULL, but kfree() handles that */ + kfree(info); + return ERR_PTR(err); +} + +static __user void *mpx_get_bounds_dir(void) +{ + const struct mpx_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. + */ + bndcsr = get_xsave_field_ptr(XFEATURE_MASK_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(void) +{ + void __user *bd_base = MPX_INVALID_BOUNDS_DIR; + struct mm_struct *mm = current->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. + * + * The copy_xregs_to_kernel() beneath get_xsave_field_ptr() is + * expected to be relatively expensive. Storing the bounds + * directory here means that we do not have to do xsave in the + * unmap path; we can just use mm->context.bd_addr instead. + */ + bd_base = mpx_get_bounds_dir(); + down_write(&mm->mmap_sem); + + /* MPX doesn't support addresses above 47 bits yet. */ + if (find_vma(mm, DEFAULT_MAP_WINDOW)) { + pr_warn_once("%s (%d): MPX cannot handle addresses " + "above 47-bits. Disabling.", + current->comm, current->pid); + ret = -ENXIO; + goto out; + } + mm->context.bd_addr = bd_base; + if (mm->context.bd_addr == MPX_INVALID_BOUNDS_DIR) + ret = -ENXIO; +out: + up_write(&mm->mmap_sem); + return ret; +} + +int mpx_disable_management(void) +{ + struct mm_struct *mm = current->mm; + + if (!cpu_feature_enabled(X86_FEATURE_MPX)) + return -ENXIO; + + down_write(&mm->mmap_sem); + mm->context.bd_addr = MPX_INVALID_BOUNDS_DIR; + up_write(&mm->mmap_sem); + return 0; +} + +static int mpx_cmpxchg_bd_entry(struct mm_struct *mm, + unsigned long *curval, + unsigned long __user *addr, + unsigned long old_val, unsigned long new_val) +{ + int ret; + /* + * user_atomic_cmpxchg_inatomic() actually uses sizeof() + * the pointer that we pass to it to figure out how much + * data to cmpxchg. We have to be careful here not to + * pass a pointer to a 64-bit data type when we only want + * a 32-bit copy. + */ + if (is_64bit_mm(mm)) { + ret = user_atomic_cmpxchg_inatomic(curval, + addr, old_val, new_val); + } else { + u32 uninitialized_var(curval_32); + u32 old_val_32 = old_val; + u32 new_val_32 = new_val; + u32 __user *addr_32 = (u32 __user *)addr; + + ret = user_atomic_cmpxchg_inatomic(&curval_32, + addr_32, old_val_32, new_val_32); + *curval = curval_32; + } + return ret; +} + +/* + * With 32-bit mode, a bounds directory is 4MB, and the size of each + * bounds table is 16KB. With 64-bit mode, a bounds directory is 2GB, + * and the size of each bounds table is 4MB. + */ +static int allocate_bt(struct mm_struct *mm, long __user *bd_entry) +{ + unsigned long expected_old_val = 0; + unsigned long actual_old_val = 0; + unsigned long bt_addr; + unsigned long bd_new_entry; + int ret = 0; + + /* + * Carve the virtual space out of userspace for the new + * bounds table: + */ + bt_addr = mpx_mmap(mpx_bt_size_bytes(mm)); + if (IS_ERR((void *)bt_addr)) + return PTR_ERR((void *)bt_addr); + /* + * Set the valid flag (kinda like _PAGE_PRESENT in a pte) + */ + bd_new_entry = 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 = mpx_cmpxchg_bd_entry(mm, &actual_old_val, bd_entry, + expected_old_val, bd_new_entry); + 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; + } + trace_mpx_new_bounds_table(bt_addr); + return 0; +out_unmap: + vm_munmap(bt_addr, mpx_bt_size_bytes(mm)); + 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(void) +{ + unsigned long bd_entry, bd_base; + const struct mpx_bndcsr *bndcsr; + struct mm_struct *mm = current->mm; + + bndcsr = get_xsave_field_ptr(XFEATURE_MASK_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(mm))) + return -EINVAL; + + return allocate_bt(mm, (long __user *)bd_entry); +} + +int mpx_handle_bd_fault(void) +{ + /* + * Userspace never asked us to manage the bounds tables, + * so refuse to help. + */ + if (!kernel_managing_mpx_tables(current->mm)) + return -EINVAL; + + return do_mpx_bt_fault(); +} + +/* + * 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; + + gup_ret = get_user_pages((unsigned long)addr, nr_pages, + write ? FOLL_WRITE : 0, 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; +} + +static unsigned long mpx_bd_entry_to_bt_addr(struct mm_struct *mm, + unsigned long bd_entry) +{ + unsigned long bt_addr = bd_entry; + int align_to_bytes; + /* + * Bit 0 in a bt_entry is always the valid bit. + */ + bt_addr &= ~MPX_BD_ENTRY_VALID_FLAG; + /* + * Tables are naturally aligned at 8-byte boundaries + * on 64-bit and 4-byte boundaries on 32-bit. The + * documentation makes it appear that the low bits + * are ignored by the hardware, so we do the same. + */ + if (is_64bit_mm(mm)) + align_to_bytes = 8; + else + align_to_bytes = 4; + bt_addr &= ~(align_to_bytes-1); + return bt_addr; +} + +/* + * We only want to do a 4-byte get_user() on 32-bit. Otherwise, + * we might run off the end of the bounds table if we are on + * a 64-bit kernel and try to get 8 bytes. + */ +static int get_user_bd_entry(struct mm_struct *mm, unsigned long *bd_entry_ret, + long __user *bd_entry_ptr) +{ + u32 bd_entry_32; + int ret; + + if (is_64bit_mm(mm)) + return get_user(*bd_entry_ret, bd_entry_ptr); + + /* + * Note that get_user() uses the type of the *pointer* to + * establish the size of the get, not the destination. + */ + ret = get_user(bd_entry_32, (u32 __user *)bd_entry_ptr); + *bd_entry_ret = bd_entry_32; + return ret; +} + +/* + * 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_ptr, + unsigned long *bt_addr_result) +{ + int ret; + int valid_bit; + unsigned long bd_entry; + unsigned long bt_addr; + + if (!access_ok(VERIFY_READ, (bd_entry_ptr), sizeof(*bd_entry_ptr))) + return -EFAULT; + + while (1) { + int need_write = 0; + + pagefault_disable(); + ret = get_user_bd_entry(mm, &bd_entry, bd_entry_ptr); + pagefault_enable(); + if (!ret) + break; + if (ret == -EFAULT) + ret = mpx_resolve_fault(bd_entry_ptr, need_write); + /* + * If we could not resolve the fault, consider it + * userspace's fault and error out. + */ + if (ret) + return ret; + } + + valid_bit = bd_entry & MPX_BD_ENTRY_VALID_FLAG; + bt_addr = mpx_bd_entry_to_bt_addr(mm, bd_entry); + + /* + * 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; + + *bt_addr_result = bt_addr; + return 0; +} + +static inline int bt_entry_size_bytes(struct mm_struct *mm) +{ + if (is_64bit_mm(mm)) + return MPX_BT_ENTRY_BYTES_64; + else + return MPX_BT_ENTRY_BYTES_32; +} + +/* + * Take a virtual address and turns it in to the offset in bytes + * inside of the bounds table where the bounds table entry + * controlling 'addr' can be found. + */ +static unsigned long mpx_get_bt_entry_offset_bytes(struct mm_struct *mm, + unsigned long addr) +{ + unsigned long bt_table_nr_entries; + unsigned long offset = addr; + + if (is_64bit_mm(mm)) { + /* Bottom 3 bits are ignored on 64-bit */ + offset >>= 3; + bt_table_nr_entries = MPX_BT_NR_ENTRIES_64; + } else { + /* Bottom 2 bits are ignored on 32-bit */ + offset >>= 2; + bt_table_nr_entries = MPX_BT_NR_ENTRIES_32; + } + /* + * We know the size of the table in to which we are + * indexing, and we have eliminated all the low bits + * which are ignored for indexing. + * + * Mask out all the high bits which we do not need + * to index in to the table. Note that the tables + * are always powers of two so this gives us a proper + * mask. + */ + offset &= (bt_table_nr_entries-1); + /* + * We now have an entry offset in terms of *entries* in + * the table. We need to scale it back up to bytes. + */ + offset *= bt_entry_size_bytes(mm); + return offset; +} + +/* + * How much virtual address space does a single bounds + * directory entry cover? + * + * Note, we need a long long because 4GB doesn't fit in + * to a long on 32-bit. + */ +static inline unsigned long bd_entry_virt_space(struct mm_struct *mm) +{ + unsigned long long virt_space; + unsigned long long GB = (1ULL << 30); + + /* + * This covers 32-bit emulation as well as 32-bit kernels + * running on 64-bit hardware. + */ + if (!is_64bit_mm(mm)) + return (4ULL * GB) / MPX_BD_NR_ENTRIES_32; + + /* + * 'x86_virt_bits' returns what the hardware is capable + * of, and returns the full >32-bit address space when + * running 32-bit kernels on 64-bit hardware. + */ + virt_space = (1ULL << boot_cpu_data.x86_virt_bits); + return virt_space / MPX_BD_NR_ENTRIES_64; +} + +/* + * Free the backing physical pages of bounds table 'bt_addr'. + * Assume start...end is within that bounds table. + */ +static noinline int zap_bt_entries_mapping(struct mm_struct *mm, + unsigned long bt_addr, + unsigned long start_mapping, unsigned long end_mapping) +{ + struct vm_area_struct *vma; + unsigned long addr, len; + unsigned long start; + unsigned long end; + + /* + * if we 'end' on a boundary, the offset will be 0 which + * is not what we want. Back it up a byte to get the + * last bt entry. Then once we have the entry itself, + * move 'end' back up by the table entry size. + */ + start = bt_addr + mpx_get_bt_entry_offset_bytes(mm, start_mapping); + end = bt_addr + mpx_get_bt_entry_offset_bytes(mm, end_mapping - 1); + /* + * Move end back up by one entry. Among other things + * this ensures that it remains page-aligned and does + * not screw up zap_page_range() + */ + end += bt_entry_size_bytes(mm); + + /* + * 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 bounds 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 (!(vma->vm_flags & VM_MPX)) + return -EINVAL; + + len = min(vma->vm_end, end) - addr; + zap_page_range(vma, addr, len); + trace_mpx_unmap_zap(addr, addr+len); + + vma = vma->vm_next; + addr = vma->vm_start; + } + return 0; +} + +static unsigned long mpx_get_bd_entry_offset(struct mm_struct *mm, + unsigned long addr) +{ + /* + * There are several ways to derive the bd offsets. We + * use the following approach here: + * 1. We know the size of the virtual address space + * 2. We know the number of entries in a bounds table + * 3. We know that each entry covers a fixed amount of + * virtual address space. + * So, we can just divide the virtual address by the + * virtual space used by one entry to determine which + * entry "controls" the given virtual address. + */ + if (is_64bit_mm(mm)) { + int bd_entry_size = 8; /* 64-bit pointer */ + /* + * Take the 64-bit addressing hole in to account. + */ + addr &= ((1UL << boot_cpu_data.x86_virt_bits) - 1); + return (addr / bd_entry_virt_space(mm)) * bd_entry_size; + } else { + int bd_entry_size = 4; /* 32-bit pointer */ + /* + * 32-bit has no hole so this case needs no mask + */ + return (addr / bd_entry_virt_space(mm)) * bd_entry_size; + } + /* + * The two return calls above are exact copies. If we + * pull out a single copy and put it in here, gcc won't + * realize that we're doing a power-of-2 divide and use + * shifts. It uses a real divide. If we put them up + * there, it manages to figure it out (gcc 4.8.3). + */ +} + +static int unmap_entire_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 uninitialized_var(actual_old_val); + int ret; + + while (1) { + int need_write = 1; + unsigned long cleared_bd_entry = 0; + + pagefault_disable(); + ret = mpx_cmpxchg_bd_entry(mm, &actual_old_val, + bd_entry, expected_old_val, cleared_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; + } + /* + * The cmpxchg was performed, check the results. + */ + if (actual_old_val != expected_old_val) { + /* + * Someone else raced with us to unmap the table. + * That is OK, since we were both trying to do + * the same thing. Declare success. + */ + 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(mm), NULL); +} + +static int try_unmap_single_bt(struct mm_struct *mm, + unsigned long start, unsigned long end) +{ + struct vm_area_struct *next; + struct vm_area_struct *prev; + /* + * "bta" == Bounds Table Area: the area controlled by the + * bounds table that we are unmapping. + */ + unsigned long bta_start_vaddr = start & ~(bd_entry_virt_space(mm)-1); + unsigned long bta_end_vaddr = bta_start_vaddr + bd_entry_virt_space(mm); + unsigned long uninitialized_var(bt_addr); + void __user *bde_vaddr; + int ret; + /* + * We already unlinked 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); + /* + * Do not count other MPX bounds table VMAs as neighbors. + * Although theoretically possible, we do not allow bounds + * tables for bounds tables so our heads do not explode. + * If we count them as neighbors here, we may end up with + * lots of tables even though we have no actual table + * entries in use. + */ + while (next && (next->vm_flags & VM_MPX)) + next = next->vm_next; + while (prev && (prev->vm_flags & VM_MPX)) + prev = prev->vm_prev; + /* + * We know 'start' and 'end' lie within an area controlled + * by a single bounds table. See if there are any other + * VMAs controlled by that bounds table. If there are not + * then we can "expand" the are we are unmapping to possibly + * cover the entire table. + */ + next = find_vma_prev(mm, start, &prev); + if ((!prev || prev->vm_end <= bta_start_vaddr) && + (!next || next->vm_start >= bta_end_vaddr)) { + /* + * No neighbor VMAs controlled by same bounds + * table. Try to unmap the whole thing + */ + start = bta_start_vaddr; + end = bta_end_vaddr; + } + + bde_vaddr = mm->context.bd_addr + mpx_get_bd_entry_offset(mm, start); + ret = get_bt_addr(mm, bde_vaddr, &bt_addr); + /* + * No bounds table there, so nothing to unmap. + */ + if (ret == -ENOENT) { + ret = 0; + return 0; + } + if (ret) + return ret; + /* + * We are unmapping an entire table. Either because the + * unmap that started this whole process was large enough + * to cover an entire table, or that the unmap was small + * but was the area covered by a bounds table. + */ + if ((start == bta_start_vaddr) && + (end == bta_end_vaddr)) + return unmap_entire_bt(mm, bde_vaddr, bt_addr); + return zap_bt_entries_mapping(mm, bt_addr, start, end); +} + +static int mpx_unmap_tables(struct mm_struct *mm, + unsigned long start, unsigned long end) +{ + unsigned long one_unmap_start; + trace_mpx_unmap_search(start, end); + + one_unmap_start = start; + while (one_unmap_start < end) { + int ret; + unsigned long next_unmap_start = ALIGN(one_unmap_start+1, + bd_entry_virt_space(mm)); + unsigned long one_unmap_end = end; + /* + * if the end is beyond the current bounds table, + * move it back so we only deal with a single one + * at a time + */ + if (one_unmap_end > next_unmap_start) + one_unmap_end = next_unmap_start; + ret = try_unmap_single_bt(mm, one_unmap_start, one_unmap_end); + if (ret) + return ret; + + one_unmap_start = next_unmap_start; + } + 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); +} + +/* MPX cannot handle addresses above 47 bits yet. */ +unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len, + unsigned long flags) +{ + if (!kernel_managing_mpx_tables(current->mm)) + return addr; + if (addr + len <= DEFAULT_MAP_WINDOW) + return addr; + if (flags & MAP_FIXED) + return -ENOMEM; + + /* + * Requested len is larger than the whole area we're allowed to map in. + * Resetting hinting address wouldn't do much good -- fail early. + */ + if (len > DEFAULT_MAP_WINDOW) + return -ENOMEM; + + /* Look for unmap area within DEFAULT_MAP_WINDOW */ + return 0; +} |