arch/arm64/kvm/va_layout.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2017 ARM Ltd.
   4  * Author: Marc Zyngier <marc.zyngier@arm.com>
   5  */
   6
   7 #include <linux/kvm_host.h>
   8 #include <linux/random.h>
   9 #include <linux/memblock.h>
  10 #include <asm/alternative.h>
  11 #include <asm/debug-monitors.h>
  12 #include <asm/insn.h>
  13 #include <asm/kvm_mmu.h>
  14 #include <asm/memory.h>
  15
  16 /*
  17  * The LSB of the HYP VA tag
  18  */
  19 static u8 tag_lsb;
  20 /*
  21  * The HYP VA tag value with the region bit
  22  */
  23 static u64 tag_val;
  24 static u64 va_mask;
  25
  26 /*
  27  * Compute HYP VA by using the same computation as kern_hyp_va().
  28  */
  29 static u64 __early_kern_hyp_va(u64 addr)
  30 {
  31         addr &= va_mask;
  32         addr |= tag_val << tag_lsb;
  33         return addr;
  34 }
  35
  36 /*
  37  * Store a hyp VA <-> PA offset into a EL2-owned variable.
  38  */
  39 static void init_hyp_physvirt_offset(void)
  40 {
  41         u64 kern_va, hyp_va;
  42
  43         /* Compute the offset from the hyp VA and PA of a random symbol. */
  44         kern_va = (u64)lm_alias(__hyp_text_start);
  45         hyp_va = __early_kern_hyp_va(kern_va);
  46         hyp_physvirt_offset = (s64)__pa(kern_va) - (s64)hyp_va;
  47 }
  48
  49 /*
  50  * We want to generate a hyp VA with the following format (with V ==
  51  * vabits_actual):
  52  *
  53  *  63 ... V |     V-1    | V-2 .. tag_lsb | tag_lsb - 1 .. 0
  54  *  ---------------------------------------------------------
  55  * | 0000000 | hyp_va_msb |   random tag   |  kern linear VA |
  56  *           |--------- tag_val -----------|----- va_mask ---|
  57  *
  58  * which does not conflict with the idmap regions.
  59  */
  60 __init void kvm_compute_layout(void)
  61 {
  62         phys_addr_t idmap_addr = __pa_symbol(__hyp_idmap_text_start);
  63         u64 hyp_va_msb;
  64
  65         /* Where is my RAM region? */
  66         hyp_va_msb  = idmap_addr & BIT(vabits_actual - 1);
  67         hyp_va_msb ^= BIT(vabits_actual - 1);
  68
  69         tag_lsb = fls64((u64)phys_to_virt(memblock_start_of_DRAM()) ^
  70                         (u64)(high_memory - 1));
  71
  72         va_mask = GENMASK_ULL(tag_lsb - 1, 0);
  73         tag_val = hyp_va_msb;
  74
  75         if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && tag_lsb != (vabits_actual - 1)) {
  76                 /* We have some free bits to insert a random tag. */
  77                 tag_val |= get_random_long() & GENMASK_ULL(vabits_actual - 2, tag_lsb);
  78         }
  79         tag_val >>= tag_lsb;
  80
  81         init_hyp_physvirt_offset();
  82 }
  83
  84 static u32 compute_instruction(int n, u32 rd, u32 rn)
  85 {
  86         u32 insn = AARCH64_BREAK_FAULT;
  87
  88         switch (n) {
  89         case 0:
  90                 insn = aarch64_insn_gen_logical_immediate(AARCH64_INSN_LOGIC_AND,
  91                                                           AARCH64_INSN_VARIANT_64BIT,
  92                                                           rn, rd, va_mask);
  93                 break;
  94
  95         case 1:
  96                 /* ROR is a variant of EXTR with Rm = Rn */
  97                 insn = aarch64_insn_gen_extr(AARCH64_INSN_VARIANT_64BIT,
  98                                              rn, rn, rd,
  99                                              tag_lsb);
 100                 break;
 101
 102         case 2:
 103                 insn = aarch64_insn_gen_add_sub_imm(rd, rn,
 104                                                     tag_val & GENMASK(11, 0),
 105                                                     AARCH64_INSN_VARIANT_64BIT,
 106                                                     AARCH64_INSN_ADSB_ADD);
 107                 break;
 108
 109         case 3:
 110                 insn = aarch64_insn_gen_add_sub_imm(rd, rn,
 111                                                     tag_val & GENMASK(23, 12),
 112                                                     AARCH64_INSN_VARIANT_64BIT,
 113                                                     AARCH64_INSN_ADSB_ADD);
 114                 break;
 115
 116         case 4:
 117                 /* ROR is a variant of EXTR with Rm = Rn */
 118                 insn = aarch64_insn_gen_extr(AARCH64_INSN_VARIANT_64BIT,
 119                                              rn, rn, rd, 64 - tag_lsb);
 120                 break;
 121         }
 122
 123         return insn;
 124 }
 125
 126 void __init kvm_update_va_mask(struct alt_instr *alt,
 127                                __le32 *origptr, __le32 *updptr, int nr_inst)
 128 {
 129         int i;
 130
 131         BUG_ON(nr_inst != 5);
 132
 133         for (i = 0; i < nr_inst; i++) {
 134                 u32 rd, rn, insn, oinsn;
 135
 136                 /*
 137                  * VHE doesn't need any address translation, let's NOP
 138                  * everything.
 139                  *
 140                  * Alternatively, if the tag is zero (because the layout
 141                  * dictates it and we don't have any spare bits in the
 142                  * address), NOP everything after masking the kernel VA.
 143                  */
 144                 if (has_vhe() || (!tag_val && i > 0)) {
 145                         updptr[i] = cpu_to_le32(aarch64_insn_gen_nop());
 146                         continue;
 147                 }
 148
 149                 oinsn = le32_to_cpu(origptr[i]);
 150                 rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, oinsn);
 151                 rn = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RN, oinsn);
 152
 153                 insn = compute_instruction(i, rd, rn);
 154                 BUG_ON(insn == AARCH64_BREAK_FAULT);
 155
 156                 updptr[i] = cpu_to_le32(insn);
 157         }
 158 }
 159
 160 void kvm_patch_vector_branch(struct alt_instr *alt,
 161                              __le32 *origptr, __le32 *updptr, int nr_inst)
 162 {
 163         u64 addr;
 164         u32 insn;
 165
 166         BUG_ON(nr_inst != 4);
 167
 168         if (!cpus_have_const_cap(ARM64_SPECTRE_V3A) || WARN_ON_ONCE(has_vhe()))
 169                 return;
 170
 171         /*
 172          * Compute HYP VA by using the same computation as kern_hyp_va()
 173          */
 174         addr = __early_kern_hyp_va((u64)kvm_ksym_ref(__kvm_hyp_vector));
 175
 176         /* Use PC[10:7] to branch to the same vector in KVM */
 177         addr |= ((u64)origptr & GENMASK_ULL(10, 7));
 178
 179         /*
 180          * Branch over the preamble in order to avoid the initial store on
 181          * the stack (which we already perform in the hardening vectors).
 182          */
 183         addr += KVM_VECTOR_PREAMBLE;
 184
 185         /* movz x0, #(addr & 0xffff) */
 186         insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0,
 187                                          (u16)addr,
 188                                          0,
 189                                          AARCH64_INSN_VARIANT_64BIT,
 190                                          AARCH64_INSN_MOVEWIDE_ZERO);
 191         *updptr++ = cpu_to_le32(insn);
 192
 193         /* movk x0, #((addr >> 16) & 0xffff), lsl #16 */
 194         insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0,
 195                                          (u16)(addr >> 16),
 196                                          16,
 197                                          AARCH64_INSN_VARIANT_64BIT,
 198                                          AARCH64_INSN_MOVEWIDE_KEEP);
 199         *updptr++ = cpu_to_le32(insn);
 200
 201         /* movk x0, #((addr >> 32) & 0xffff), lsl #32 */
 202         insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_0,
 203                                          (u16)(addr >> 32),
 204                                          32,
 205                                          AARCH64_INSN_VARIANT_64BIT,
 206                                          AARCH64_INSN_MOVEWIDE_KEEP);
 207         *updptr++ = cpu_to_le32(insn);
 208
 209         /* br x0 */
 210         insn = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_0,
 211                                            AARCH64_INSN_BRANCH_NOLINK);
 212         *updptr++ = cpu_to_le32(insn);
 213 }
 214
 215 static void generate_mov_q(u64 val, __le32 *origptr, __le32 *updptr, int nr_inst)
 216 {
 217         u32 insn, oinsn, rd;
 218
 219         BUG_ON(nr_inst != 4);
 220
 221         /* Compute target register */
 222         oinsn = le32_to_cpu(*origptr);
 223         rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, oinsn);
 224
 225         /* movz rd, #(val & 0xffff) */
 226         insn = aarch64_insn_gen_movewide(rd,
 227                                          (u16)val,
 228                                          0,
 229                                          AARCH64_INSN_VARIANT_64BIT,
 230                                          AARCH64_INSN_MOVEWIDE_ZERO);
 231         *updptr++ = cpu_to_le32(insn);
 232
 233         /* movk rd, #((val >> 16) & 0xffff), lsl #16 */
 234         insn = aarch64_insn_gen_movewide(rd,
 235                                          (u16)(val >> 16),
 236                                          16,
 237                                          AARCH64_INSN_VARIANT_64BIT,
 238                                          AARCH64_INSN_MOVEWIDE_KEEP);
 239         *updptr++ = cpu_to_le32(insn);
 240
 241         /* movk rd, #((val >> 32) & 0xffff), lsl #32 */
 242         insn = aarch64_insn_gen_movewide(rd,
 243                                          (u16)(val >> 32),
 244                                          32,
 245                                          AARCH64_INSN_VARIANT_64BIT,
 246                                          AARCH64_INSN_MOVEWIDE_KEEP);
 247         *updptr++ = cpu_to_le32(insn);
 248
 249         /* movk rd, #((val >> 48) & 0xffff), lsl #48 */
 250         insn = aarch64_insn_gen_movewide(rd,
 251                                          (u16)(val >> 48),
 252                                          48,
 253                                          AARCH64_INSN_VARIANT_64BIT,
 254                                          AARCH64_INSN_MOVEWIDE_KEEP);
 255         *updptr++ = cpu_to_le32(insn);
 256 }
 257
 258 void kvm_update_kimg_phys_offset(struct alt_instr *alt,
 259                                  __le32 *origptr, __le32 *updptr, int nr_inst)
 260 {
 261         generate_mov_q(kimage_voffset + PHYS_OFFSET, origptr, updptr, nr_inst);
 262 }
 263
 264 void kvm_get_kimage_voffset(struct alt_instr *alt,
 265                             __le32 *origptr, __le32 *updptr, int nr_inst)
 266 {
 267         generate_mov_q(kimage_voffset, origptr, updptr, nr_inst);
 268 }