| // Copyright 2020 The Fuchsia Authors |
| // |
| // Use of this source code is governed by a MIT-style |
| // license that can be found in the LICENSE file or at |
| // https://opensource.org/licenses/MIT |
| |
| #include <fbl/conditional_select_nospec.h> |
| #include <fbl/confine_array_index.h> |
| #include <sys/types.h> |
| |
| namespace internal { |
| |
| // Confines vaddr, len to [0, top]; if [|vaddr|, |vaddr + len|] are above top, return {0,0} |
| // Does so without any conditional branches, avoiding Spectre V1 attacks. |
| // |
| // Confines both vaddr and len by following the sequence: |
| // vaddr_lo = vaddr <= top ? vaddr : 0 |
| // vaddr_hi = vaddr + len <= top : vaddr + len : 0 |
| // *vaddr = (len == vaddr_hi - vaddr_lo) ? vaddr_lo : 0 |
| // *len = (len == vaddr_hi - vaddr_lo) ? len : 0 |
| void confine_user_address_range(vaddr_t* vaddr, size_t* len, const uintptr_t top) { |
| const size_t vaddr_lo = fbl::confine_array_index(*vaddr, top + 1); |
| const size_t vaddr_hi = fbl::confine_array_index(*vaddr + *len, top + 1); |
| *vaddr = fbl::conditional_select_nospec_eq(*len, vaddr_hi - vaddr_lo, vaddr_lo, 0); |
| *len = fbl::conditional_select_nospec_eq(*len, vaddr_hi - vaddr_lo, *len, 0); |
| } |
| |
| } // namespace internal |
