1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 /* 3 * AMD Memory Encryption Support 4 * 5 * Copyright (C) 2017 Advanced Micro Devices, Inc. 6 * 7 * Author: Tom Lendacky <thomas.lendacky@amd.com> 8 */ 9 10 #include <linux/linkage.h> 11 12 #include <asm/processor-flags.h> 13 #include <asm/msr.h> 14 #include <asm/asm-offsets.h> 15 #include <asm/segment.h> 16 #include <asm/trapnr.h> 17 18 .text 19 .code32 20 SYM_FUNC_START(get_sev_encryption_bit) 21 push %ebx 22 23 movl $0x80000000, %eax /* CPUID to check the highest leaf */ 24 cpuid 25 cmpl $0x8000001f, %eax /* See if 0x8000001f is available */ 26 jb .Lno_sev 27 28 /* 29 * Check for the SEV feature: 30 * CPUID Fn8000_001F[EAX] - Bit 1 31 * CPUID Fn8000_001F[EBX] - Bits 5:0 32 * Pagetable bit position used to indicate encryption 33 */ 34 movl $0x8000001f, %eax 35 cpuid 36 bt $1, %eax /* Check if SEV is available */ 37 jnc .Lno_sev 38 39 movl $MSR_AMD64_SEV, %ecx /* Read the SEV MSR */ 40 rdmsr 41 bt $MSR_AMD64_SEV_ENABLED_BIT, %eax /* Check if SEV is active */ 42 jnc .Lno_sev 43 44 movl %ebx, %eax 45 andl $0x3f, %eax /* Return the encryption bit location */ 46 jmp .Lsev_exit 47 48 .Lno_sev: 49 xor %eax, %eax 50 51 .Lsev_exit: 52 pop %ebx 53 RET 54 SYM_FUNC_END(get_sev_encryption_bit) 55 56 /** 57 * sev_es_req_cpuid - Request a CPUID value from the Hypervisor using 58 * the GHCB MSR protocol 59 * 60 * @%eax: Register to request (0=EAX, 1=EBX, 2=ECX, 3=EDX) 61 * @%edx: CPUID Function 62 * 63 * Returns 0 in %eax on success, non-zero on failure 64 * %edx returns CPUID value on success 65 */ 66 SYM_CODE_START_LOCAL(sev_es_req_cpuid) 67 shll $30, %eax 68 orl $0x00000004, %eax 69 movl $MSR_AMD64_SEV_ES_GHCB, %ecx 70 wrmsr 71 rep; vmmcall # VMGEXIT 72 rdmsr 73 74 /* Check response */ 75 movl %eax, %ecx 76 andl $0x3ffff000, %ecx # Bits [12-29] MBZ 77 jnz 2f 78 79 /* Check return code */ 80 andl $0xfff, %eax 81 cmpl $5, %eax 82 jne 2f 83 84 /* All good - return success */ 85 xorl %eax, %eax 86 1: 87 RET 88 2: 89 movl $-1, %eax 90 jmp 1b 91 SYM_CODE_END(sev_es_req_cpuid) 92 93 SYM_CODE_START_LOCAL(startup32_vc_handler) 94 pushl %eax 95 pushl %ebx 96 pushl %ecx 97 pushl %edx 98 99 /* Keep CPUID function in %ebx */ 100 movl %eax, %ebx 101 102 /* Check if error-code == SVM_EXIT_CPUID */ 103 cmpl $0x72, 16(%esp) 104 jne .Lfail 105 106 movl $0, %eax # Request CPUID[fn].EAX 107 movl %ebx, %edx # CPUID fn 108 call sev_es_req_cpuid # Call helper 109 testl %eax, %eax # Check return code 110 jnz .Lfail 111 movl %edx, 12(%esp) # Store result 112 113 movl $1, %eax # Request CPUID[fn].EBX 114 movl %ebx, %edx # CPUID fn 115 call sev_es_req_cpuid # Call helper 116 testl %eax, %eax # Check return code 117 jnz .Lfail 118 movl %edx, 8(%esp) # Store result 119 120 movl $2, %eax # Request CPUID[fn].ECX 121 movl %ebx, %edx # CPUID fn 122 call sev_es_req_cpuid # Call helper 123 testl %eax, %eax # Check return code 124 jnz .Lfail 125 movl %edx, 4(%esp) # Store result 126 127 movl $3, %eax # Request CPUID[fn].EDX 128 movl %ebx, %edx # CPUID fn 129 call sev_es_req_cpuid # Call helper 130 testl %eax, %eax # Check return code 131 jnz .Lfail 132 movl %edx, 0(%esp) # Store result 133 134 /* 135 * Sanity check CPUID results from the Hypervisor. See comment in 136 * do_vc_no_ghcb() for more details on why this is necessary. 137 */ 138 139 /* Fail if SEV leaf not available in CPUID[0x80000000].EAX */ 140 cmpl $0x80000000, %ebx 141 jne .Lcheck_sev 142 cmpl $0x8000001f, 12(%esp) 143 jb .Lfail 144 jmp .Ldone 145 146 .Lcheck_sev: 147 /* Fail if SEV bit not set in CPUID[0x8000001f].EAX[1] */ 148 cmpl $0x8000001f, %ebx 149 jne .Ldone 150 btl $1, 12(%esp) 151 jnc .Lfail 152 153 .Ldone: 154 popl %edx 155 popl %ecx 156 popl %ebx 157 popl %eax 158 159 /* Remove error code */ 160 addl $4, %esp 161 162 /* Jump over CPUID instruction */ 163 addl $2, (%esp) 164 165 iret 166 .Lfail: 167 /* Send terminate request to Hypervisor */ 168 movl $0x100, %eax 169 xorl %edx, %edx 170 movl $MSR_AMD64_SEV_ES_GHCB, %ecx 171 wrmsr 172 rep; vmmcall 173 174 /* If request fails, go to hlt loop */ 175 hlt 176 jmp .Lfail 177 SYM_CODE_END(startup32_vc_handler) 178 179 /* 180 * Write an IDT entry into boot32_idt 181 * 182 * Parameters: 183 * 184 * %eax: Handler address 185 * %edx: Vector number 186 * %ecx: IDT address 187 */ 188 SYM_FUNC_START_LOCAL(startup32_set_idt_entry) 189 /* IDT entry address to %ecx */ 190 leal (%ecx, %edx, 8), %ecx 191 192 /* Build IDT entry, lower 4 bytes */ 193 movl %eax, %edx 194 andl $0x0000ffff, %edx # Target code segment offset [15:0] 195 orl $(__KERNEL32_CS << 16), %edx # Target code segment selector 196 197 /* Store lower 4 bytes to IDT */ 198 movl %edx, (%ecx) 199 200 /* Build IDT entry, upper 4 bytes */ 201 movl %eax, %edx 202 andl $0xffff0000, %edx # Target code segment offset [31:16] 203 orl $0x00008e00, %edx # Present, Type 32-bit Interrupt Gate 204 205 /* Store upper 4 bytes to IDT */ 206 movl %edx, 4(%ecx) 207 208 RET 209 SYM_FUNC_END(startup32_set_idt_entry) 210 211 SYM_FUNC_START(startup32_load_idt) 212 push %ebp 213 push %ebx 214 215 call 1f 216 1: pop %ebp 217 218 leal (boot32_idt - 1b)(%ebp), %ebx 219 220 /* #VC handler */ 221 leal (startup32_vc_handler - 1b)(%ebp), %eax 222 movl $X86_TRAP_VC, %edx 223 movl %ebx, %ecx 224 call startup32_set_idt_entry 225 226 /* Load IDT */ 227 leal (boot32_idt_desc - 1b)(%ebp), %ecx 228 movl %ebx, 2(%ecx) 229 lidt (%ecx) 230 231 pop %ebx 232 pop %ebp 233 RET 234 SYM_FUNC_END(startup32_load_idt) 235 236 /* 237 * Check for the correct C-bit position when the startup_32 boot-path is used. 238 * 239 * The check makes use of the fact that all memory is encrypted when paging is 240 * disabled. The function creates 64 bits of random data using the RDRAND 241 * instruction. RDRAND is mandatory for SEV guests, so always available. If the 242 * hypervisor violates that the kernel will crash right here. 243 * 244 * The 64 bits of random data are stored to a memory location and at the same 245 * time kept in the %eax and %ebx registers. Since encryption is always active 246 * when paging is off the random data will be stored encrypted in main memory. 247 * 248 * Then paging is enabled. When the C-bit position is correct all memory is 249 * still mapped encrypted and comparing the register values with memory will 250 * succeed. An incorrect C-bit position will map all memory unencrypted, so that 251 * the compare will use the encrypted random data and fail. 252 */ 253 SYM_FUNC_START(startup32_check_sev_cbit) 254 pushl %ebx 255 pushl %ebp 256 257 call 0f 258 0: popl %ebp 259 260 /* Check for non-zero sev_status */ 261 movl (sev_status - 0b)(%ebp), %eax 262 testl %eax, %eax 263 jz 4f 264 265 /* 266 * Get two 32-bit random values - Don't bail out if RDRAND fails 267 * because it is better to prevent forward progress if no random value 268 * can be gathered. 269 */ 270 1: rdrand %eax 271 jnc 1b 272 2: rdrand %ebx 273 jnc 2b 274 275 /* Store to memory and keep it in the registers */ 276 leal (sev_check_data - 0b)(%ebp), %ebp 277 movl %eax, 0(%ebp) 278 movl %ebx, 4(%ebp) 279 280 /* Enable paging to see if encryption is active */ 281 movl %cr0, %edx /* Backup %cr0 in %edx */ 282 movl $(X86_CR0_PG | X86_CR0_PE), %ecx /* Enable Paging and Protected mode */ 283 movl %ecx, %cr0 284 285 cmpl %eax, 0(%ebp) 286 jne 3f 287 cmpl %ebx, 4(%ebp) 288 jne 3f 289 290 movl %edx, %cr0 /* Restore previous %cr0 */ 291 292 jmp 4f 293 294 3: /* Check failed - hlt the machine */ 295 hlt 296 jmp 3b 297 298 4: 299 popl %ebp 300 popl %ebx 301 RET 302 SYM_FUNC_END(startup32_check_sev_cbit) 303 304 .code64 305 306 #include "../../kernel/sev_verify_cbit.S" 307 308 .data 309 310 .balign 8 311 SYM_DATA(sme_me_mask, .quad 0) 312 SYM_DATA(sev_status, .quad 0) 313 SYM_DATA(sev_check_data, .quad 0) 314 315 SYM_DATA_START_LOCAL(boot32_idt) 316 .rept 32 317 .quad 0 318 .endr 319 SYM_DATA_END(boot32_idt) 320 321 SYM_DATA_START_LOCAL(boot32_idt_desc) 322 .word . - boot32_idt - 1 323 .long 0 324 SYM_DATA_END(boot32_idt_desc)
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