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Linux/arch/x86/math-emu/get_address.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*---------------------------------------------------------------------------+
  3  |  get_address.c                                                            |
  4  |                                                                           |
  5  | Get the effective address from an FPU instruction.                        |
  6  |                                                                           |
  7  | Copyright (C) 1992,1993,1994,1997                                         |
  8  |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
  9  |                       Australia.  E-mail   billm@suburbia.net             |
 10  |                                                                           |
 11  |                                                                           |
 12  +---------------------------------------------------------------------------*/
 13 
 14 /*---------------------------------------------------------------------------+
 15  | Note:                                                                     |
 16  |    The file contains code which accesses user memory.                     |
 17  |    Emulator static data may change when user memory is accessed, due to   |
 18  |    other processes using the emulator while swapping is in progress.      |
 19  +---------------------------------------------------------------------------*/
 20 
 21 #include <linux/stddef.h>
 22 
 23 #include <linux/uaccess.h>
 24 #include <asm/vm86.h>
 25 
 26 #include "fpu_system.h"
 27 #include "exception.h"
 28 #include "fpu_emu.h"
 29 
 30 #define FPU_WRITE_BIT 0x10
 31 
 32 static int reg_offset[] = {
 33         offsetof(struct pt_regs, ax),
 34         offsetof(struct pt_regs, cx),
 35         offsetof(struct pt_regs, dx),
 36         offsetof(struct pt_regs, bx),
 37         offsetof(struct pt_regs, sp),
 38         offsetof(struct pt_regs, bp),
 39         offsetof(struct pt_regs, si),
 40         offsetof(struct pt_regs, di)
 41 };
 42 
 43 #define REG_(x) (*(long *)(reg_offset[(x)] + (u_char *)FPU_info->regs))
 44 
 45 static int reg_offset_vm86[] = {
 46         offsetof(struct pt_regs, cs),
 47         offsetof(struct kernel_vm86_regs, ds),
 48         offsetof(struct kernel_vm86_regs, es),
 49         offsetof(struct kernel_vm86_regs, fs),
 50         offsetof(struct kernel_vm86_regs, gs),
 51         offsetof(struct pt_regs, ss),
 52         offsetof(struct kernel_vm86_regs, ds)
 53 };
 54 
 55 #define VM86_REG_(x) (*(unsigned short *) \
 56                 (reg_offset_vm86[((unsigned)x)] + (u_char *)FPU_info->regs))
 57 
 58 static int reg_offset_pm[] = {
 59         offsetof(struct pt_regs, cs),
 60         offsetof(struct pt_regs, ds),
 61         offsetof(struct pt_regs, es),
 62         offsetof(struct pt_regs, fs),
 63         offsetof(struct pt_regs, ds),   /* dummy, not saved on stack */
 64         offsetof(struct pt_regs, ss),
 65         offsetof(struct pt_regs, ds)
 66 };
 67 
 68 #define PM_REG_(x) (*(unsigned short *) \
 69                 (reg_offset_pm[((unsigned)x)] + (u_char *)FPU_info->regs))
 70 
 71 /* Decode the SIB byte. This function assumes mod != 0 */
 72 static int sib(int mod, unsigned long *fpu_eip)
 73 {
 74         u_char ss, index, base;
 75         long offset;
 76 
 77         RE_ENTRANT_CHECK_OFF;
 78         FPU_code_access_ok(1);
 79         FPU_get_user(base, (u_char __user *) (*fpu_eip));       /* The SIB byte */
 80         RE_ENTRANT_CHECK_ON;
 81         (*fpu_eip)++;
 82         ss = base >> 6;
 83         index = (base >> 3) & 7;
 84         base &= 7;
 85 
 86         if ((mod == 0) && (base == 5))
 87                 offset = 0;     /* No base register */
 88         else
 89                 offset = REG_(base);
 90 
 91         if (index == 4) {
 92                 /* No index register */
 93                 /* A non-zero ss is illegal */
 94                 if (ss)
 95                         EXCEPTION(EX_Invalid);
 96         } else {
 97                 offset += (REG_(index)) << ss;
 98         }
 99 
100         if (mod == 1) {
101                 /* 8 bit signed displacement */
102                 long displacement;
103                 RE_ENTRANT_CHECK_OFF;
104                 FPU_code_access_ok(1);
105                 FPU_get_user(displacement, (signed char __user *)(*fpu_eip));
106                 offset += displacement;
107                 RE_ENTRANT_CHECK_ON;
108                 (*fpu_eip)++;
109         } else if (mod == 2 || base == 5) {     /* The second condition also has mod==0 */
110                 /* 32 bit displacement */
111                 long displacement;
112                 RE_ENTRANT_CHECK_OFF;
113                 FPU_code_access_ok(4);
114                 FPU_get_user(displacement, (long __user *)(*fpu_eip));
115                 offset += displacement;
116                 RE_ENTRANT_CHECK_ON;
117                 (*fpu_eip) += 4;
118         }
119 
120         return offset;
121 }
122 
123 static unsigned long vm86_segment(u_char segment, struct address *addr)
124 {
125         segment--;
126 #ifdef PARANOID
127         if (segment > PREFIX_SS_) {
128                 EXCEPTION(EX_INTERNAL | 0x130);
129                 math_abort(FPU_info, SIGSEGV);
130         }
131 #endif /* PARANOID */
132         addr->selector = VM86_REG_(segment);
133         return (unsigned long)VM86_REG_(segment) << 4;
134 }
135 
136 /* This should work for 16 and 32 bit protected mode. */
137 static long pm_address(u_char FPU_modrm, u_char segment,
138                        struct address *addr, long offset)
139 {
140         struct desc_struct descriptor;
141         unsigned long base_address, limit, address, seg_top;
142 
143         segment--;
144 
145 #ifdef PARANOID
146         /* segment is unsigned, so this also detects if segment was 0: */
147         if (segment > PREFIX_SS_) {
148                 EXCEPTION(EX_INTERNAL | 0x132);
149                 math_abort(FPU_info, SIGSEGV);
150         }
151 #endif /* PARANOID */
152 
153         switch (segment) {
154         case PREFIX_GS_ - 1:
155                 /* user gs handling can be lazy, use special accessors */
156                 addr->selector = get_user_gs(FPU_info->regs);
157                 break;
158         default:
159                 addr->selector = PM_REG_(segment);
160         }
161 
162         descriptor = FPU_get_ldt_descriptor(addr->selector);
163         base_address = seg_get_base(&descriptor);
164         address = base_address + offset;
165         limit = seg_get_limit(&descriptor) + 1;
166         limit *= seg_get_granularity(&descriptor);
167         limit += base_address - 1;
168         if (limit < base_address)
169                 limit = 0xffffffff;
170 
171         if (seg_expands_down(&descriptor)) {
172                 if (descriptor.g) {
173                         seg_top = 0xffffffff;
174                 } else {
175                         seg_top = base_address + (1 << 20);
176                         if (seg_top < base_address)
177                                 seg_top = 0xffffffff;
178                 }
179                 access_limit =
180                     (address <= limit) || (address >= seg_top) ? 0 :
181                     ((seg_top - address) >= 255 ? 255 : seg_top - address);
182         } else {
183                 access_limit =
184                     (address > limit) || (address < base_address) ? 0 :
185                     ((limit - address) >= 254 ? 255 : limit - address + 1);
186         }
187         if (seg_execute_only(&descriptor) ||
188             (!seg_writable(&descriptor) && (FPU_modrm & FPU_WRITE_BIT))) {
189                 access_limit = 0;
190         }
191         return address;
192 }
193 
194 /*
195        MOD R/M byte:  MOD == 3 has a special use for the FPU
196                       SIB byte used iff R/M = 100b
197 
198        7   6   5   4   3   2   1   0
199        .....   .........   .........
200         MOD    OPCODE(2)     R/M
201 
202        SIB byte
203 
204        7   6   5   4   3   2   1   0
205        .....   .........   .........
206         SS      INDEX        BASE
207 
208 */
209 
210 void __user *FPU_get_address(u_char FPU_modrm, unsigned long *fpu_eip,
211                              struct address *addr, fpu_addr_modes addr_modes)
212 {
213         u_char mod;
214         unsigned rm = FPU_modrm & 7;
215         long *cpu_reg_ptr;
216         int address = 0;        /* Initialized just to stop compiler warnings. */
217 
218         /* Memory accessed via the cs selector is write protected
219            in `non-segmented' 32 bit protected mode. */
220         if (!addr_modes.default_mode && (FPU_modrm & FPU_WRITE_BIT)
221             && (addr_modes.override.segment == PREFIX_CS_)) {
222                 math_abort(FPU_info, SIGSEGV);
223         }
224 
225         addr->selector = FPU_DS;        /* Default, for 32 bit non-segmented mode. */
226 
227         mod = (FPU_modrm >> 6) & 3;
228 
229         if (rm == 4 && mod != 3) {
230                 address = sib(mod, fpu_eip);
231         } else {
232                 cpu_reg_ptr = &REG_(rm);
233                 switch (mod) {
234                 case 0:
235                         if (rm == 5) {
236                                 /* Special case: disp32 */
237                                 RE_ENTRANT_CHECK_OFF;
238                                 FPU_code_access_ok(4);
239                                 FPU_get_user(address,
240                                              (unsigned long __user
241                                               *)(*fpu_eip));
242                                 (*fpu_eip) += 4;
243                                 RE_ENTRANT_CHECK_ON;
244                                 addr->offset = address;
245                                 return (void __user *)address;
246                         } else {
247                                 address = *cpu_reg_ptr; /* Just return the contents
248                                                            of the cpu register */
249                                 addr->offset = address;
250                                 return (void __user *)address;
251                         }
252                 case 1:
253                         /* 8 bit signed displacement */
254                         RE_ENTRANT_CHECK_OFF;
255                         FPU_code_access_ok(1);
256                         FPU_get_user(address, (signed char __user *)(*fpu_eip));
257                         RE_ENTRANT_CHECK_ON;
258                         (*fpu_eip)++;
259                         break;
260                 case 2:
261                         /* 32 bit displacement */
262                         RE_ENTRANT_CHECK_OFF;
263                         FPU_code_access_ok(4);
264                         FPU_get_user(address, (long __user *)(*fpu_eip));
265                         (*fpu_eip) += 4;
266                         RE_ENTRANT_CHECK_ON;
267                         break;
268                 case 3:
269                         /* Not legal for the FPU */
270                         EXCEPTION(EX_Invalid);
271                 }
272                 address += *cpu_reg_ptr;
273         }
274 
275         addr->offset = address;
276 
277         switch (addr_modes.default_mode) {
278         case 0:
279                 break;
280         case VM86:
281                 address += vm86_segment(addr_modes.override.segment, addr);
282                 break;
283         case PM16:
284         case SEG32:
285                 address = pm_address(FPU_modrm, addr_modes.override.segment,
286                                      addr, address);
287                 break;
288         default:
289                 EXCEPTION(EX_INTERNAL | 0x133);
290         }
291 
292         return (void __user *)address;
293 }
294 
295 void __user *FPU_get_address_16(u_char FPU_modrm, unsigned long *fpu_eip,
296                                 struct address *addr, fpu_addr_modes addr_modes)
297 {
298         u_char mod;
299         unsigned rm = FPU_modrm & 7;
300         int address = 0;        /* Default used for mod == 0 */
301 
302         /* Memory accessed via the cs selector is write protected
303            in `non-segmented' 32 bit protected mode. */
304         if (!addr_modes.default_mode && (FPU_modrm & FPU_WRITE_BIT)
305             && (addr_modes.override.segment == PREFIX_CS_)) {
306                 math_abort(FPU_info, SIGSEGV);
307         }
308 
309         addr->selector = FPU_DS;        /* Default, for 32 bit non-segmented mode. */
310 
311         mod = (FPU_modrm >> 6) & 3;
312 
313         switch (mod) {
314         case 0:
315                 if (rm == 6) {
316                         /* Special case: disp16 */
317                         RE_ENTRANT_CHECK_OFF;
318                         FPU_code_access_ok(2);
319                         FPU_get_user(address,
320                                      (unsigned short __user *)(*fpu_eip));
321                         (*fpu_eip) += 2;
322                         RE_ENTRANT_CHECK_ON;
323                         goto add_segment;
324                 }
325                 break;
326         case 1:
327                 /* 8 bit signed displacement */
328                 RE_ENTRANT_CHECK_OFF;
329                 FPU_code_access_ok(1);
330                 FPU_get_user(address, (signed char __user *)(*fpu_eip));
331                 RE_ENTRANT_CHECK_ON;
332                 (*fpu_eip)++;
333                 break;
334         case 2:
335                 /* 16 bit displacement */
336                 RE_ENTRANT_CHECK_OFF;
337                 FPU_code_access_ok(2);
338                 FPU_get_user(address, (unsigned short __user *)(*fpu_eip));
339                 (*fpu_eip) += 2;
340                 RE_ENTRANT_CHECK_ON;
341                 break;
342         case 3:
343                 /* Not legal for the FPU */
344                 EXCEPTION(EX_Invalid);
345                 break;
346         }
347         switch (rm) {
348         case 0:
349                 address += FPU_info->regs->bx + FPU_info->regs->si;
350                 break;
351         case 1:
352                 address += FPU_info->regs->bx + FPU_info->regs->di;
353                 break;
354         case 2:
355                 address += FPU_info->regs->bp + FPU_info->regs->si;
356                 if (addr_modes.override.segment == PREFIX_DEFAULT)
357                         addr_modes.override.segment = PREFIX_SS_;
358                 break;
359         case 3:
360                 address += FPU_info->regs->bp + FPU_info->regs->di;
361                 if (addr_modes.override.segment == PREFIX_DEFAULT)
362                         addr_modes.override.segment = PREFIX_SS_;
363                 break;
364         case 4:
365                 address += FPU_info->regs->si;
366                 break;
367         case 5:
368                 address += FPU_info->regs->di;
369                 break;
370         case 6:
371                 address += FPU_info->regs->bp;
372                 if (addr_modes.override.segment == PREFIX_DEFAULT)
373                         addr_modes.override.segment = PREFIX_SS_;
374                 break;
375         case 7:
376                 address += FPU_info->regs->bx;
377                 break;
378         }
379 
380       add_segment:
381         address &= 0xffff;
382 
383         addr->offset = address;
384 
385         switch (addr_modes.default_mode) {
386         case 0:
387                 break;
388         case VM86:
389                 address += vm86_segment(addr_modes.override.segment, addr);
390                 break;
391         case PM16:
392         case SEG32:
393                 address = pm_address(FPU_modrm, addr_modes.override.segment,
394                                      addr, address);
395                 break;
396         default:
397                 EXCEPTION(EX_INTERNAL | 0x131);
398         }
399 
400         return (void __user *)address;
401 }
402 

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