1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857
//! Security-hardened buffers for storing sensitive data in memory. //! //! This crate provides hardened buffer types backed by memory allocated using //! [libsodium](https://libsodium.org)'s [secure memory management //! utilities](https://doc.libsodium.org/memory_management#guarded-heap-allocations). The intention //! is to provide types for securely storing sensitive data (cryptographic keys, passwords, etc). //! //! Memory allocated using hard is placed directly at the end of a page, followed by a guard page, //! so any buffer overflow will immediately result in the termination of the program. A canary is //! placed before the allocated memory to detect modifications on free, and another guard page is //! placed before this. Finally, operating system is advised not to swap the memory to disk, or //! include it in crash reports/core dumps. //! //! Hard also provides an interface for marking memory as read-only/no-access when its //! modification/access is not required. This can be used to protect sensitive data from access //! while not in use. //! //! # Examples //! ```rust //! use hard::{buffer_type, Buffer, BufferMut}; //! //! // Create a new public buffer type, which will store 32 bytes (= 256 bits) of sensitive data: //! buffer_type! { //! /// Stores a 256-bit key. //! pub Key(32); //! } //! //! // The new type implements a couple of basic traits for its construction and initialisation: //! let mut my_key = Key::new().unwrap(); //! my_key.zero(); //! //! // It also implements `Deref`, and similar types associated with smart pointers, so we can //! // treat it like an array [u8; 32]: //! my_key.copy_from_slice(b"Some data to store in the buffer"); //! my_key[0] ^= 0xab; //! my_key[1] ^= 0xcd; //! //! // Mark the buffer as read-only, which will prevent modification to its contents: //! let my_key = my_key.into_readonly().unwrap(); //! //! // When the buffer is dropped, its contents are securely erased, preventing leakage of the //! // contents via uninitialised memory. //! ``` //! //! We can also create anonymous buffers, which provide access to hardened memory without the need //! to worry about creating new types for whatever operation we perform: //! //! ```rust //! use hard::{buffer, Buffer, BufferMut}; //! //! // Create a 512 byte buffer. //! let mut some_data = buffer!(512).unwrap(); //! //! // Copy in some data //! some_data.copy_from_slice(&[0xab; 512]); //! //! // Debugging a buffer does not directly print its contents, although deref'ing it does do so. //! println!("{:?}, {:?}", some_data, *some_data); //! //! // Once again, dropping the buffer erases its contents. //! ``` //! //! For more information, see the [`buffer`] and [`buffer_type`] macros, and the traits the buffer //! types implement: [`Buffer`], [`BufferMut`], [`BufferReadOnly`], [`BufferNoAccess`]. pub mod mem; use errno::Errno; use libsodium_sys as sodium; use thiserror::Error; /// Represents an error encountered while using Hard. #[derive(Clone, Copy, Debug, Eq, Error, PartialEq)] pub enum HardError { /// `sodium_malloc` returned an error when we tried to allocate a region of memory. /// /// This is most likely to occur if there is not sufficient memory to allocate, but could occur /// for other reasons. The associated value contains the value of the errno value, which is set /// if `sodium_malloc` fails. #[error("Failed to allocate secure memory region")] AllocationFailed(Errno), /// `sodium_mprotect_noaccess` returned an error. /// /// This is most likely to occur if the platform we're running on doesn't have the `mprotect` /// syscall (or its equivalent). #[error("Failed to mark memory region as noaccess (syscall may not be available)")] MprotectNoAccessFailed(Errno), /// `sodium_mprotect_readonly` returned an error. /// /// This is most likely to occur if the platform we're running on doesn't have the `mprotect` /// syscall (or its equivalent). #[error("Failed to mark memory region as readonly (syscall may not be available)")] MprotectReadOnlyFailed(Errno), /// `sodium_mprotect_readwrite` returned an error. /// /// This is most likely to occur if the platform we're running on doesn't have the `mprotect` /// syscall (or its equivalent). #[error("Failed to mark memory region as read/write (syscall may not be available)")] MprotectReadWriteFailed(Errno), /// `sodium_init` returned an error. #[error("Failed to initialise libsodium")] InitFailed, } /// Trait implemented by any buffer type generated with [`buffer_type`]. pub trait Buffer where Self: Sized, { /// The size of this buffer, in bytes. const SIZE: usize; /// Create a new instance of the buffer, filled with garbage data. fn new() -> Result<Self, HardError>; } /// Trait implemented by any buffer type with mutable contents. pub trait BufferMut: Buffer where Self: Sized, { /// The variant of this buffer that is locked such that its contents cannot be accessed. type NoAccess: BufferNoAccess; /// The variant of this buffer that is locked such that its contents cannot be mutated, /// although they can be read. type ReadOnly: BufferReadOnly; /// Overwrite the contents of the buffer with zeros, in such a way that will not be optimised /// away by the compiler. /// /// Buffers are automatically zeroed on drop, you should not need to call this method yourself /// unless you want to set a buffer to zero for initialisation purposes. fn zero(&mut self); /// Attempt to clone this buffer. /// /// This will allocate a new region of memory, and copy the contents of this buffer into it. fn try_clone(&self) -> Result<Self, HardError>; /// `mprotect` the region of memory pointed to by this buffer, so that it cannot be accessed. /// /// This function uses the operating system's memory protection tools to mark the region of /// memory backing this buffer as inaccessible. This is used as a hardening measure, to protect /// the region of memory so that it can't be accessed by anything while we don't need it. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_noaccess(self) -> Result<Self::NoAccess, HardError>; /// `mprotect` the region of memory pointed to by this buffer, so that it cannot be mutated, /// although it can still be read. /// /// This function uses the operating system's memory protection tools to mark the region of /// memory backing this buffer as read-only. This is used as a hardening measure, to protect /// the region of memory so that it can't be altered by anything. This would be well suited to, /// for example, secure a key after key generation, since there is no need to modify a key once /// we've generated it in most cases. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_readonly(self) -> Result<Self::ReadOnly, HardError>; } /// Trait implemented by any buffer type whose memory is marked no-access. pub trait BufferNoAccess: Buffer where Self: Sized, { /// The mutable variant of this buffer. type ReadWrite: BufferMut; /// The variant of this buffer that is locked such that its contents cannot be mutated, /// although they can be read. type ReadOnly: BufferReadOnly; /// Remove protections for this buffer that marked it as noaccess, so it can be read and /// modified. /// /// This basically just marks the memory underlying this buffer as the same as any normal /// memory, so it can be read or modified again, although sodium's hardening measures (guard /// pages, canaries, mlock, etc.) remain in place. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_mut(self) -> Result<Self::ReadWrite, HardError>; /// `mprotect` the region of memory pointed to by this buffer, so that it cannot be mutated, /// although it can still be read. /// /// This function uses the operating system's memory protection tools to mark the region of /// memory backing this buffer as read-only. This is used as a hardening measure, to protect /// the region of memory so that it can't be altered by anything. This would be well suited to, /// for example, secure a key after key generation, since there is no need to modify a key once /// we've generated it in most cases. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_readonly(self) -> Result<Self::ReadOnly, HardError>; } /// Trait implemented by any buffer type whose memory is marked read-only. pub trait BufferReadOnly: Buffer where Self: Sized, { /// The mutable variant of this buffer. type ReadWrite: BufferMut; /// The variant of this buffer that is locked such that its contents cannot be accessed. type NoAccess: BufferNoAccess; /// Attempt to clone this buffer. /// /// This will allocate a new region of memory, and copy the contents of this buffer into it. fn try_clone(&self) -> Result<Self, HardError>; /// Remove protections for this buffer that marked it as noaccess, so it can be read and /// modified. /// /// This basically just marks the memory underlying this buffer as the same as any normal /// memory, so it can be read or modified again, although sodium's hardening measures (guard /// pages, canaries, mlock, etc.) remain in place. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_mut(self) -> Result<Self::ReadWrite, HardError>; /// `mprotect` the region of memory pointed to by this buffer, so that it cannot be accessed. /// /// This function uses the operating system's memory protection tools to mark the region of /// memory backing this buffer as inaccessible. This is used as a hardening measure, to protect /// the region of memory so that it can't be accessed by anything while we don't need it. /// /// If there is no `mprotect` (or equivalent) syscall on this platform, this function will /// return an error. fn into_noaccess(self) -> Result<Self::NoAccess, HardError>; } #[doc(hidden)] pub unsafe trait BufferAsPtr: Buffer where Self: Sized, { /// Returns the pointer to the memory backing this type. /// /// We use this to implement PartialEq for buffer types using `sodium_memcmp`, which needs a /// pointer to both portions of memory we're comparing. /// /// # Safety /// This function returns a pointer to raw memory, any modification to its contents or /// protection status could violate the safety invariants required for this buffer type to be /// safe. Therefore, it should only be used where the memory it points to will not be modified, /// and any use should be documented. unsafe fn as_ptr(&self) -> std::ptr::NonNull<()>; } #[macro_export] #[doc(hidden)] macro_rules! buffer_common_impl { ($name:ident, $size:expr) => { impl Drop for $name { fn drop(&mut self) { // SAFETY: // * Is a double-free possible in safe code? // * No: `drop` cannot be called manually, and is only called once when the // buffer is actually dropped. Once the value is dropped, there's no way to // free the memory again. In methods that produce other buffers (e.g: // `try_clone`, `into_noaccess`), we either allocate new memory for the new // buffer, or use `ManuallyDrop` to avoid calling drop more than once. // * Is a use-after-free possible in safe code? // * No: We only ever free a buffer on drop. and after drop, the buffer type is // no longer accessible. // * Is a memory leak possible in safe code? // * Yes: If the user uses `Box::leak()`, `ManuallyDrop`, or `std::mem::forget`, // the destructor will not be called even though the buffer is dropped. // However, it is documented that in these cases heap memory may be leaked, so // this is expected behaviour. In addition, certain signal interrupts, or // setting panic=abort, will mean that the destructor is not called. In any // other case, `drop` will be called, and the memory freed. unsafe { $crate::mem::free(self.0); } } } }; } #[macro_export] #[doc(hidden)] macro_rules! buffer_immutable_impl { ($name:ident, $size:expr) => { #[doc(hidden)] unsafe impl $crate::BufferAsPtr for $name { unsafe fn as_ptr(&self) -> std::ptr::NonNull<()> { self.0.cast() } } impl std::convert::AsRef<[u8; $size]> for $name { fn as_ref(&self) -> &[u8; $size] { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that of // the struct, as the memory is only freed on drop. Any portion of memory of length // T is a valid array of `u8`s of size T, so initialisation & alignment issues are // not a concern. unsafe { self.0.as_ref() } } } impl std::borrow::Borrow<[u8; $size]> for $name { fn borrow(&self) -> &[u8; $size] { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that of // the struct, as the memory is only freed on drop. Any portion of memory of length // T is a valid array of `u8`s of size T, so initialisation & alignment issues are // not a concern. unsafe { self.0.as_ref() } } } impl std::fmt::Debug for $name { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { f.write_str(&format!("{}([u8; {}])", stringify!($name), $size)) } } impl std::ops::Deref for $name { type Target = [u8; $size]; fn deref(&self) -> &Self::Target { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that of // the struct, as the memory is only freed on drop. Any portion of memory of length // T is a valid array of `u8`s of size T, so initialisation & alignment issues are // not a concern. unsafe { self.0.as_ref() } } } impl<T: $crate::Buffer + $crate::BufferAsPtr> std::cmp::PartialEq<T> for $name { fn eq(&self, other: &T) -> bool { if T::SIZE != Self::SIZE { return false; } // SAFETY: We make use of the unsafe method `Self::as_ptr` here, which requires // that we do not modify the memory to which its return value points. The `memcmp` // function simply compares two pointers, they will not be modified. As both `self` // and `other` are instances of a Buffer, we know they must point to sufficient, // allocated memory for their types, so the memcmp call is safe. unsafe { $crate::mem::memcmp(self.0, other.as_ptr().cast()) } } } impl std::fmt::Pointer for $name { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> { <std::ptr::NonNull<[u8; $size]> as std::fmt::Pointer>::fmt(&self.0, f) } } }; } #[macro_export] #[doc(hidden)] macro_rules! buffer_mutable_impl { ($name:ident, $size:expr) => { paste::paste! { $crate::buffer_common_impl!($name, $size); $crate::buffer_immutable_impl!($name, $size); impl $crate::Buffer for $name { const SIZE: usize = $size; fn new() -> Result<Self, $crate::HardError> { $crate::init()?; // SAFETY: This call to malloc() will allocate the memory required for a [u8; // $size] type, outside of Rust's memory management. The associated memory is // always freed in the corresponding `drop` call. We never free the memory in // any other method of this struct, nor do we ever give out a pointer to the // memory directly, only references. The region of memory allocated will always // a valid representation of a [u8; $size], as a [u8; $size] is simply // represented as $size bytes of memory, of arbitrary values. The alignment for // a u8 is just 1, so we don't need to worry about alignment issues. let ptr = unsafe { $crate::mem::malloc()? }; Ok(Self(ptr)) } } impl $crate::BufferMut for $name { type NoAccess = [<$name NoAccess>]; type ReadOnly = [<$name ReadOnly>]; fn zero(&mut self) { // SAFETY: While a buffer is in scope, its memory is valid. It is therefore // safe to write zeroes to the buffer. All zeroes is a valid memory // representation of a u8 array. unsafe { $crate::mem::memzero(self.0) } } fn try_clone(&self) -> Result<Self, $crate::HardError> { let mut new_buf = Self::new()?; new_buf.copy_from_slice(self.as_ref()); Ok(new_buf) } fn into_noaccess(self) -> Result<Self::NoAccess, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_noaccess(self_leak.0)?; } Ok([<$name NoAccess>](self_leak.0)) } fn into_readonly(self) -> Result<Self::ReadOnly, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_readonly(self_leak.0)?; } Ok([<$name ReadOnly>](self_leak.0)) } } impl std::convert::AsMut<[u8; $size]> for $name { fn as_mut(&mut self) -> &mut [u8; $size] { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that // of the struct, as the memory is only freed on drop. Any portion of memory of // length T is a valid array of `u8`s of size T, so initialisation & alignment // issues are not a concern. unsafe { self.0.as_mut() } } } impl std::borrow::BorrowMut<[u8; $size]> for $name { fn borrow_mut(&mut self) -> &mut [u8; $size] { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that // of the struct, as the memory is only freed on drop. Any portion of memory of // length T is a valid array of `u8`s of size T, so initialisation & alignment // issues are not a concern. unsafe { self.0.as_mut() } } } impl std::ops::DerefMut for $name { fn deref_mut(&mut self) -> &mut Self::Target { // SAFETY: As long as a buffer type exists, the memory backing it is // dereferenceable and non-null. The lifetime of the returned reference is that // of the struct, as the memory is only freed on drop. Any portion of memory of // length T is a valid array of `u8`s of size T, so initialisation & alignment // issues are not a concern. unsafe { self.0.as_mut() } } } } }; } #[macro_export] #[doc(hidden)] macro_rules! buffer_noaccess_impl { ($name:ident, $size:expr) => { paste::paste! { $crate::buffer_common_impl!([<$name NoAccess>], $size); impl $crate::Buffer for [<$name NoAccess>] { const SIZE: usize = $size; fn new() -> Result<Self, $crate::HardError> { $crate::init()?; // SAFETY: This call to malloc() will allocate the memory required for a [u8; // $size] type, outside of Rust's memory management. The associated memory is // always freed in the corresponding `drop` call. We never free the memory in // any other method of this struct, nor do we ever give out a pointer to the // memory directly, only references. The region of memory allocated will always // a valid representation of a [u8; $size], as a [u8; $size] is simply // represented as $size bytes of memory, of arbitrary values. The alignment for // a u8 is just 1, so we don't need to worry about alignment issues. let ptr = unsafe { let ptr = $crate::mem::malloc()?; $crate::mem::mprotect_noaccess(ptr)?; ptr }; Ok(Self(ptr)) } } impl $crate::BufferNoAccess for [<$name NoAccess>] { type ReadWrite = $name; type ReadOnly = [<$name ReadOnly>]; fn into_mut(self) -> Result<Self::ReadWrite, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_readwrite(self_leak.0)?; } Ok($name(self_leak.0)) } fn into_readonly(self) -> Result<Self::ReadOnly, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_readonly(self_leak.0)?; } Ok([<$name ReadOnly>](self_leak.0)) } } } }; } #[macro_export] #[doc(hidden)] macro_rules! buffer_readonly_impl { ($name:ident, $size:expr) => { paste::paste! { $crate::buffer_common_impl!([<$name ReadOnly>], $size); $crate::buffer_immutable_impl!([<$name ReadOnly>], $size); impl $crate::Buffer for [<$name ReadOnly>] { const SIZE: usize = $size; fn new() -> Result<Self, $crate::HardError> { $crate::init()?; // SAFETY: This call to malloc() will allocate the memory required for a [u8; // $size] type, outside of Rust's memory management. The associated memory is // always freed in the corresponding `drop` call. We never free the memory in // any other method of this struct, nor do we ever give out a pointer to the // memory directly, only references. The region of memory allocated will always // a valid representation of a [u8; $size], as a [u8; $size] is simply // represented as $size bytes of memory, of arbitrary values. The alignment for // a u8 is just 1, so we don't need to worry about alignment issues. let ptr = unsafe { let ptr = $crate::mem::malloc()?; $crate::mem::mprotect_readonly(ptr)?; ptr }; Ok(Self(ptr)) } } impl $crate::BufferReadOnly for [<$name ReadOnly>] { type ReadWrite = $name; type NoAccess = [<$name NoAccess>]; fn try_clone(&self) -> Result<Self, $crate::HardError> { use $crate::BufferMut; let mut new_buf = $name::new()?; new_buf.copy_from_slice(self.as_ref()); new_buf.into_readonly() } fn into_mut(self) -> Result<Self::ReadWrite, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_readwrite(self_leak.0)?; } Ok($name(self_leak.0)) } fn into_noaccess(self) -> Result<Self::NoAccess, $crate::HardError> { // SAFETY: Avoid calling self.drop() when self goes out of scope, so as to // avoid freeing the underlying memory. We use the underlying memory in the new // type, so when it goes out of scope, the memory will then be freed. let self_leak = std::mem::ManuallyDrop::new(self); // SAFETY: The buffer is currently in scope, so its backing memory is valid. unsafe { $crate::mem::mprotect_noaccess(self_leak.0)?; } Ok([<$name NoAccess>](self_leak.0)) } } } }; } /// Create a new fixed-size buffer type. /// /// `buffer_type!(Name(Size))` will create a new type with name `Name`, that provides access to /// `Size` bytes of hardened contiguous memory. /// /// The new type will implement the following traits: /// * [`Buffer`] and [`BufferMut`] /// * [`AsRef<[u8; Size]>`](std::convert::AsRef) and [`AsMut<[u8; Size]>`](std::convert::AsMut) /// * [`Borrow<[u8; $size]>`](std::borrow::Borrow) and [`BorrowMut<[u8; /// * [`Debug`](std::fmt::Debug) /// * [`Deref<Target = [u8; Size]>`](std::ops::Deref) and [`DerefMut`](std::ops::DerefMut) /// $size]>`](std::borrow::BorrowMut) /// * [`PartialEq<Rhs = BufferMut or BufferReadOnly>`](std::cmp::PartialEq) and /// [`Eq`](std::cmp::Eq) /// * This implementation uses a constant-time comparison function for equivalent-sized buffers, /// suitable for comparing sensitive data without the risk of timing attacks. /// * [`Pointer`](std::fmt::Pointer) /// /// This macro also generates `NameNoAccess` and `NameReadOnly` variants, which use the operating /// system's memory protection utilities to mark the buffer's contents as completely inaccessible, /// and immutable, respectively. /// /// ## Example Usage /// ```rust /// use hard::{buffer_type, Buffer}; /// /// // Create a 32-byte (256-bit) buffer type called `Key` /// buffer_type!(Key(32)); /// let mut my_key = Key::new().unwrap(); /// // The type implements Deref<Target = [u8; 32]> and DerefMut, so we can use any methods from /// // the array type. /// my_key.copy_from_slice(b"Some data to copy into my_key..."); /// my_key[0] ^= 0xca; /// println!("{:x?}", my_key); /// /// // By default, a new buffer type will be private, but we can specify that it should be public. /// buffer_type!(pub Password(128)); /// /// // We can also provide documentation for the newly generated type, if we like. /// buffer_type! { /// /// This type stores some very important information /// pub ImportantBuf(99); /// } /// ``` #[macro_export] macro_rules! buffer_type { ($(#[$metadata:meta])* $name:ident($size:expr)$(;)?) => { paste::paste! { $(#[$metadata])* struct $name(std::ptr::NonNull<[u8; $size]>); $crate::buffer_mutable_impl!($name, $size); /// Variation of this buffer type whose contents are restricted from being accessed. struct [<$name NoAccess>](std::ptr::NonNull<[u8; $size]>); $crate::buffer_noaccess_impl!($name, $size); /// Variation of this buffer type whose contents are restricted from being mutated. struct [<$name ReadOnly>](std::ptr::NonNull<[u8; $size]>); $crate::buffer_readonly_impl!($name, $size); } }; ($(#[$metadata:meta])* pub $name:ident($size:expr)$(;)?) => { paste::paste! { $(#[$metadata])* pub struct $name(std::ptr::NonNull<[u8; $size]>); $crate::buffer_mutable_impl!($name, $size); /// Variation of this buffer type whose contents are restricted from being accessed. pub struct [<$name NoAccess>](std::ptr::NonNull<[u8; $size]>); $crate::buffer_noaccess_impl!($name, $size); /// Variation of this buffer type whose contents are restricted from being mutated. pub struct [<$name ReadOnly>](std::ptr::NonNull<[u8; $size]>); $crate::buffer_readonly_impl!($name, $size); } }; } /// Create a fixed-size anonymous buffer. /// /// `buffer!(Size)` will initialise a new buffer of length `Size` bytes, returning /// `Result<Buffer, HardError>`. /// /// The buffer will implement the following traits: /// * [`Buffer`] and [`BufferMut`] /// * [`AsRef<[u8; Size]>`](std::convert::AsRef) and [`AsMut<[u8; Size]>`](std::convert::AsMut) /// * [`Borrow<[u8; $size]>`](std::borrow::Borrow) and [`BorrowMut<[u8; /// * [`Debug`](std::fmt::Debug) /// * [`Deref<Target = [u8; Size]>`](std::ops::Deref) and [`DerefMut`](std::ops::DerefMut) /// $size]>`](std::borrow::BorrowMut) /// * [`PartialEq<Rhs = BufferMut or BufferReadOnly>`](std::cmp::PartialEq) and /// [`Eq`](std::cmp::Eq) /// * This implementation uses a constant-time comparison function, suitable for comparing /// sensitive data without the risk of timing attacks. /// * [`Pointer`](std::fmt::Pointer) /// /// ## Example Usage /// ```rust /// use hard::buffer; /// /// // Create a 32-byte buffer /// let mut some_buffer = buffer!(32).unwrap(); /// some_buffer.copy_from_slice(b"Copy this data into that buffer."); /// /// let mut another_buffer = buffer!(32).unwrap(); /// some_buffer.copy_from_slice(b"We'll compare these two buffers."); /// /// // This comparison is a constant-time equality-check of the contents of the two buffers /// assert!(some_buffer != another_buffer); /// ``` #[macro_export] macro_rules! buffer { ($size:expr$(;)?) => {{ paste::paste! { use $crate::Buffer; $crate::buffer_type!([<_HardAnonBuffer $size>]($size)); [<_HardAnonBuffer $size>]::new() } }}; } /// Initialise Sodium. /// /// This function is automatically called when a buffer is initialised. It can safely be called /// multiple times from multiple threads. You should not need to call this function yourself, but /// it's not an issue if you do. pub fn init() -> Result<(), HardError> { // SAFETY: Sodium guarantees that this function is thread safe, and can be called multiple // times without issue. It should not produce any unsafe behaviour. If it returns a // non-negative value, then Sodium has been securely initialised, and can be used throughout // the program. unsafe { if sodium::sodium_init() >= 0 { Ok(()) } else { Err(HardError::InitFailed) } } } #[cfg(test)] mod tests { use super::{ buffer, buffer_type, init, Buffer, BufferMut, BufferNoAccess, BufferReadOnly, HardError, }; use std::borrow::{Borrow, BorrowMut}; use std::ops::DerefMut; #[test] fn initialise_sodium() -> Result<(), HardError> { init() } #[test] fn create_buffer_types() -> Result<(), HardError> { buffer_type!(Buf8(8)); buffer_type!(pub Buf32(32)); buffer_type! { /// Documented Buf512(512) } buffer_type! { /// Public and documented pub Buf1MiB(1 << 20) } assert_eq!(Buf8::SIZE, 8); assert_eq!(Buf32::SIZE, 32); assert_eq!(Buf512::SIZE, 512); assert_eq!(Buf1MiB::SIZE, 1 << 20); let buf_8 = Buf8::new()?; let buf_32 = Buf32::new()?; let buf_512 = Buf512::new()?; let buf_mib = Buf1MiB::new()?; assert_eq!(buf_8.len(), 8); assert_eq!(buf_32.len(), 32); assert_eq!(buf_512.len(), 512); assert_eq!(buf_mib.len(), 1 << 20); Ok(()) } #[test] fn create_anonymous_buffers() -> Result<(), HardError> { let buf_8_a = buffer!(8)?; let buf_8_b = buffer!(8)?; let buf_32 = buffer!(32)?; let buf_512 = buffer!(512)?; let buf_mib = buffer!(0x100000)?; assert_eq!(buf_8_a.len(), 8); assert_eq!(buf_8_b.len(), 8); assert_eq!(buf_32.len(), 32); assert_eq!(buf_512.len(), 512); assert_eq!(buf_mib.len(), 1 << 20); Ok(()) } #[test] fn buffer_traits() -> Result<(), HardError> { let mut buf = buffer!(32)?; buf.zero(); let buf_b = buf.try_clone()?; assert_eq!(buf, buf_b); let buf = buf.into_noaccess()?; let buf = buf.into_mut()?; let buf = buf.into_readonly()?; let buf_c = buf.try_clone()?; assert_eq!(buf, buf_c); let buf = buf.into_noaccess()?; let buf = buf.into_readonly()?; let buf = buf.into_mut()?; assert_eq!(*buf, [0; 32]); Ok(()) } #[test] fn immutable_common_trait_impls() -> Result<(), HardError> { let mut buf = buffer!(32)?; buf.zero(); // AsRef assert_eq!(buf.as_ref(), &[0; 32]); // Borrow let buf_ref: &[u8; 32] = buf.borrow(); assert_eq!(buf_ref, &[0; 32]); // Debug format!("{:?}", buf); // Deref assert_eq!(*buf, [0; 32]); // PartialEq let mut other = buffer!(32)?; other.zero(); assert_eq!(buf, other); // Pointer format!("{:p}", buf); Ok(()) } #[test] fn mutable_common_trait_impls() -> Result<(), HardError> { let mut buf = buffer!(32)?; buf.zero(); // AsMut assert_eq!(buf.as_mut(), &mut [0; 32]); // BorrowMut let buf_ref: &mut [u8; 32] = buf.borrow_mut(); assert_eq!(buf_ref, &mut [0; 32]); // DerefMut assert_eq!(buf.deref_mut(), &mut [0; 32]); Ok(()) } }