+++ /dev/null
-.. SPDX-License-Identifier: GPL-2.0
-
-===========================================
-Intel(R) Memory Protection Extensions (MPX)
-===========================================
-
-Intel(R) MPX Overview
-=====================
-
-Intel(R) Memory Protection Extensions (Intel(R) MPX) is a new capability
-introduced into Intel Architecture. Intel MPX provides hardware features
-that can be used in conjunction with compiler changes to check memory
-references, for those references whose compile-time normal intentions are
-usurped at runtime due to buffer overflow or underflow.
-
-You can tell if your CPU supports MPX by looking in /proc/cpuinfo::
-
- cat /proc/cpuinfo | grep ' mpx '
-
-For more information, please refer to Intel(R) Architecture Instruction
-Set Extensions Programming Reference, Chapter 9: Intel(R) Memory Protection
-Extensions.
-
-Note: As of December 2014, no hardware with MPX is available but it is
-possible to use SDE (Intel(R) Software Development Emulator) instead, which
-can be downloaded from
-http://software.intel.com/en-us/articles/intel-software-development-emulator
-
-
-How to get the advantage of MPX
-===============================
-
-For MPX to work, changes are required in the kernel, binutils and compiler.
-No source changes are required for applications, just a recompile.
-
-There are a lot of moving parts of this to all work right. The following
-is how we expect the compiler, application and kernel to work together.
-
-1) Application developer compiles with -fmpx. The compiler will add the
- instrumentation as well as some setup code called early after the app
- starts. New instruction prefixes are noops for old CPUs.
-2) That setup code allocates (virtual) space for the "bounds directory",
- points the "bndcfgu" register to the directory (must also set the valid
- bit) and notifies the kernel (via the new prctl(PR_MPX_ENABLE_MANAGEMENT))
- that the app will be using MPX. The app must be careful not to access
- the bounds tables between the time when it populates "bndcfgu" and
- when it calls the prctl(). This might be hard to guarantee if the app
- is compiled with MPX. You can add "__attribute__((bnd_legacy))" to
- the function to disable MPX instrumentation to help guarantee this.
- Also be careful not to call out to any other code which might be
- MPX-instrumented.
-3) The kernel detects that the CPU has MPX, allows the new prctl() to
- succeed, and notes the location of the bounds directory. Userspace is
- expected to keep the bounds directory at that location. We note it
- instead of reading it each time because the 'xsave' operation needed
- to access the bounds directory register is an expensive operation.
-4) If the application needs to spill bounds out of the 4 registers, it
- issues a bndstx instruction. Since the bounds directory is empty at
- this point, a bounds fault (#BR) is raised, the kernel allocates a
- bounds table (in the user address space) and makes the relevant entry
- in the bounds directory point to the new table.
-5) If the application violates the bounds specified in the bounds registers,
- a separate kind of #BR is raised which will deliver a signal with
- information about the violation in the 'struct siginfo'.
-6) Whenever memory is freed, we know that it can no longer contain valid
- pointers, and we attempt to free the associated space in the bounds
- tables. If an entire table becomes unused, we will attempt to free
- the table and remove the entry in the directory.
-
-To summarize, there are essentially three things interacting here:
-
-GCC with -fmpx:
- * enables annotation of code with MPX instructions and prefixes
- * inserts code early in the application to call in to the "gcc runtime"
-GCC MPX Runtime:
- * Checks for hardware MPX support in cpuid leaf
- * allocates virtual space for the bounds directory (malloc() essentially)
- * points the hardware BNDCFGU register at the directory
- * calls a new prctl(PR_MPX_ENABLE_MANAGEMENT) to notify the kernel to
- start managing the bounds directories
-Kernel MPX Code:
- * Checks for hardware MPX support in cpuid leaf
- * Handles #BR exceptions and sends SIGSEGV to the app when it violates
- bounds, like during a buffer overflow.
- * When bounds are spilled in to an unallocated bounds table, the kernel
- notices in the #BR exception, allocates the virtual space, then
- updates the bounds directory to point to the new table. It keeps
- special track of the memory with a VM_MPX flag.
- * Frees unused bounds tables at the time that the memory they described
- is unmapped.
-
-
-How does MPX kernel code work
-=============================
-
-Handling #BR faults caused by MPX
----------------------------------
-
-When MPX is enabled, there are 2 new situations that can generate
-#BR faults.
-
- * new bounds tables (BT) need to be allocated to save bounds.
- * bounds violation caused by MPX instructions.
-
-We hook #BR handler to handle these two new situations.
-
-On-demand kernel allocation of bounds tables
---------------------------------------------
-
-MPX only has 4 hardware registers for storing bounds information. If
-MPX-enabled code needs more than these 4 registers, it needs to spill
-them somewhere. It has two special instructions for this which allow
-the bounds to be moved between the bounds registers and some new "bounds
-tables".
-
-#BR exceptions are a new class of exceptions just for MPX. They are
-similar conceptually to a page fault and will be raised by the MPX
-hardware during both bounds violations or when the tables are not
-present. The kernel handles those #BR exceptions for not-present tables
-by carving the space out of the normal processes address space and then
-pointing the bounds-directory over to it.
-
-The tables need to be accessed and controlled by userspace because
-the instructions for moving bounds in and out of them are extremely
-frequent. They potentially happen every time a register points to
-memory. Any direct kernel involvement (like a syscall) to access the
-tables would obviously destroy performance.
-
-Why not do this in userspace? MPX does not strictly require anything in
-the kernel. It can theoretically be done completely from userspace. Here
-are a few ways this could be done. We don't think any of them are practical
-in the real-world, but here they are.
-
-:Q: Can virtual space simply be reserved for the bounds tables so that we
- never have to allocate them?
-:A: MPX-enabled application will possibly create a lot of bounds tables in
- process address space to save bounds information. These tables can take
- up huge swaths of memory (as much as 80% of the memory on the system)
- even if we clean them up aggressively. In the worst-case scenario, the
- tables can be 4x the size of the data structure being tracked. IOW, a
- 1-page structure can require 4 bounds-table pages. An X-GB virtual
- area needs 4*X GB of virtual space, plus 2GB for the bounds directory.
- If we were to preallocate them for the 128TB of user virtual address
- space, we would need to reserve 512TB+2GB, which is larger than the
- entire virtual address space today. This means they can not be reserved
- ahead of time. Also, a single process's pre-populated bounds directory
- consumes 2GB of virtual *AND* physical memory. IOW, it's completely
- infeasible to prepopulate bounds directories.
-
-:Q: Can we preallocate bounds table space at the same time memory is
- allocated which might contain pointers that might eventually need
- bounds tables?
-:A: This would work if we could hook the site of each and every memory
- allocation syscall. This can be done for small, constrained applications.
- But, it isn't practical at a larger scale since a given app has no
- way of controlling how all the parts of the app might allocate memory
- (think libraries). The kernel is really the only place to intercept
- these calls.
-
-:Q: Could a bounds fault be handed to userspace and the tables allocated
- there in a signal handler instead of in the kernel?
-:A: mmap() is not on the list of safe async handler functions and even
- if mmap() would work it still requires locking or nasty tricks to
- keep track of the allocation state there.
-
-Having ruled out all of the userspace-only approaches for managing
-bounds tables that we could think of, we create them on demand in
-the kernel.
-
-Decoding MPX instructions
--------------------------
-
-If a #BR is generated due to a bounds violation caused by MPX.
-We need to decode MPX instructions to get violation address and
-set this address into extended struct siginfo.
-
-The _sigfault field of struct siginfo is extended as follow::
-
- 87 /* SIGILL, SIGFPE, SIGSEGV, SIGBUS */
- 88 struct {
- 89 void __user *_addr; /* faulting insn/memory ref. */
- 90 #ifdef __ARCH_SI_TRAPNO
- 91 int _trapno; /* TRAP # which caused the signal */
- 92 #endif
- 93 short _addr_lsb; /* LSB of the reported address */
- 94 struct {
- 95 void __user *_lower;
- 96 void __user *_upper;
- 97 } _addr_bnd;
- 98 } _sigfault;
-
-The '_addr' field refers to violation address, and new '_addr_and'
-field refers to the upper/lower bounds when a #BR is caused.
-
-Glibc will be also updated to support this new siginfo. So user
-can get violation address and bounds when bounds violations occur.
-
-Cleanup unused bounds tables
-----------------------------
-
-When a BNDSTX instruction attempts to save bounds to a bounds directory
-entry marked as invalid, a #BR is generated. This is an indication that
-no bounds table exists for this entry. In this case the fault handler
-will allocate a new bounds table on demand.
-
-Since the kernel allocated those tables on-demand without userspace
-knowledge, it is also responsible for freeing them when the associated
-mappings go away.
-
-Here, the solution for this issue is to hook do_munmap() to check
-whether one process is MPX enabled. If yes, those bounds tables covered
-in the virtual address region which is being unmapped will be freed also.
-
-Adding new prctl commands
--------------------------
-
-Two new prctl commands are added to enable and disable MPX bounds tables
-management in kernel.
-::
-
- 155 #define PR_MPX_ENABLE_MANAGEMENT 43
- 156 #define PR_MPX_DISABLE_MANAGEMENT 44
-
-Runtime library in userspace is responsible for allocation of bounds
-directory. So kernel have to use XSAVE instruction to get the base
-of bounds directory from BNDCFG register.
-
-But XSAVE is expected to be very expensive. In order to do performance
-optimization, we have to get the base of bounds directory and save it
-into struct mm_struct to be used in future during PR_MPX_ENABLE_MANAGEMENT
-command execution.
-
-
-Special rules
-=============
-
-1) If userspace is requesting help from the kernel to do the management
-of bounds tables, it may not create or modify entries in the bounds directory.
-
-Certainly users can allocate bounds tables and forcibly point the bounds
-directory at them through XSAVE instruction, and then set valid bit
-of bounds entry to have this entry valid. But, the kernel will decline
-to assist in managing these tables.
-
-2) Userspace may not take multiple bounds directory entries and point
-them at the same bounds table.
-
-This is allowed architecturally. See more information "Intel(R) Architecture
-Instruction Set Extensions Programming Reference" (9.3.4).
-
-However, if users did this, the kernel might be fooled in to unmapping an
-in-use bounds table since it does not recognize sharing.
+++ /dev/null
-// 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/mman.h>
-#include <linux/syscalls.h>
-#include <linux/sched/sysctl.h>
-
-#include <asm/insn.h>
-#include <asm/insn-eval.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...
- */
-int mpx_fault_info(struct mpx_fault_info *info, struct pt_regs *regs)
-{
- const struct mpx_bndreg_state *bndregs;
- const struct mpx_bndreg *bndreg;
- 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_BNDREGS);
- if (!bndregs) {
- err = -EINVAL;
- goto err_out;
- }
- /* now go select the individual register in the set of 4 */
- bndreg = &bndregs->bndreg[bndregno];
-
- /*
- * 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->lower = (void __user *)(unsigned long)bndreg->lower_bound;
- info->upper = (void __user *)(unsigned long)~bndreg->upper_bound;
- info->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->addr == (void __user *)-1) {
- err = -EINVAL;
- goto err_out;
- }
- trace_mpx_bounds_register_exception(info->addr, bndreg);
- return 0;
-err_out:
- /* info might be NULL, but kfree() handles that */
- return 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_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_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((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, unsigned long start,
- unsigned long end)
-{
- struct vm_area_struct *vma;
- 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.
- */
- vma = find_vma(mm, start);
- while (vma && vma->vm_start < end) {
- if (vma->vm_flags & VM_MPX)
- return;
- vma = vma->vm_next;
- }
-
- ret = mpx_unmap_tables(mm, start, end);
- if (ret)
- force_sig(SIGSEGV);
-}
-
-/* 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;
-}
projects / users / jedix / linux-maple.git / commitdiff