arch/mips/kernel/elf.c

   1 /*
   2  * Copyright (C) 2014 Imagination Technologies
   3  * Author: Paul Burton <paul.burton@imgtec.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License as published by the
   7  * Free Software Foundation;  either version 2 of the  License, or (at your
   8  * option) any later version.
   9  */
  10
  11 #include <linux/binfmts.h>
  12 #include <linux/elf.h>
  13 #include <linux/export.h>
  14 #include <linux/sched.h>
  15
  16 #include <asm/cpu-features.h>
  17 #include <asm/cpu-info.h>
  18
  19 /* Whether to accept legacy-NaN and 2008-NaN user binaries.  */
  20 bool mips_use_nan_legacy;
  21 bool mips_use_nan_2008;
  22
  23 /* FPU modes */
  24 enum {
  25         FP_FRE,
  26         FP_FR0,
  27         FP_FR1,
  28 };
  29
  30 /**
  31  * struct mode_req - ABI FPU mode requirements
  32  * @single:     The program being loaded needs an FPU but it will only issue
  33  *              single precision instructions meaning that it can execute in
  34  *              either FR0 or FR1.
  35  * @soft:       The soft(-float) requirement means that the program being
  36  *              loaded needs has no FPU dependency at all (i.e. it has no
  37  *              FPU instructions).
  38  * @fr1:        The program being loaded depends on FPU being in FR=1 mode.
  39  * @frdefault:  The program being loaded depends on the default FPU mode.
  40  *              That is FR0 for O32 and FR1 for N32/N64.
  41  * @fre:        The program being loaded depends on FPU with FRE=1. This mode is
  42  *              a bridge which uses FR=1 whilst still being able to maintain
  43  *              full compatibility with pre-existing code using the O32 FP32
  44  *              ABI.
  45  *
  46  * More information about the FP ABIs can be found here:
  47  *
  48  * https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
  49  *
  50  */
  51
  52 struct mode_req {
  53         bool single;
  54         bool soft;
  55         bool fr1;
  56         bool frdefault;
  57         bool fre;
  58 };
  59
  60 static const struct mode_req fpu_reqs[] = {
  61         [MIPS_ABI_FP_ANY]    = { true,  true,  true,  true,  true  },
  62         [MIPS_ABI_FP_DOUBLE] = { false, false, false, true,  true  },
  63         [MIPS_ABI_FP_SINGLE] = { true,  false, false, false, false },
  64         [MIPS_ABI_FP_SOFT]   = { false, true,  false, false, false },
  65         [MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
  66         [MIPS_ABI_FP_XX]     = { false, false, true,  true,  true  },
  67         [MIPS_ABI_FP_64]     = { false, false, true,  false, false },
  68         [MIPS_ABI_FP_64A]    = { false, false, true,  false, true  }
  69 };
  70
  71 /*
  72  * Mode requirements when .MIPS.abiflags is not present in the ELF.
  73  * Not present means that everything is acceptable except FR1.
  74  */
  75 static struct mode_req none_req = { true, true, false, true, true };
  76
  77 int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
  78                      bool is_interp, struct arch_elf_state *state)
  79 {
  80         union {
  81                 struct elf32_hdr e32;
  82                 struct elf64_hdr e64;
  83         } *ehdr = _ehdr;
  84         struct elf32_phdr *phdr32 = _phdr;
  85         struct elf64_phdr *phdr64 = _phdr;
  86         struct mips_elf_abiflags_v0 abiflags;
  87         bool elf32;
  88         u32 flags;
  89         int ret;
  90
  91         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
  92         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
  93
  94         /* Let's see if this is an O32 ELF */
  95         if (elf32) {
  96                 if (flags & EF_MIPS_FP64) {
  97                         /*
  98                          * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
  99                          * later if needed
 100                          */
 101                         if (is_interp)
 102                                 state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
 103                         else
 104                                 state->fp_abi = MIPS_ABI_FP_OLD_64;
 105                 }
 106                 if (phdr32->p_type != PT_MIPS_ABIFLAGS)
 107                         return 0;
 108
 109                 if (phdr32->p_filesz < sizeof(abiflags))
 110                         return -EINVAL;
 111
 112                 ret = kernel_read(elf, phdr32->p_offset,
 113                                   (char *)&abiflags,
 114                                   sizeof(abiflags));
 115         } else {
 116                 if (phdr64->p_type != PT_MIPS_ABIFLAGS)
 117                         return 0;
 118                 if (phdr64->p_filesz < sizeof(abiflags))
 119                         return -EINVAL;
 120
 121                 ret = kernel_read(elf, phdr64->p_offset,
 122                                   (char *)&abiflags,
 123                                   sizeof(abiflags));
 124         }
 125
 126         if (ret < 0)
 127                 return ret;
 128         if (ret != sizeof(abiflags))
 129                 return -EIO;
 130
 131         /* Record the required FP ABIs for use by mips_check_elf */
 132         if (is_interp)
 133                 state->interp_fp_abi = abiflags.fp_abi;
 134         else
 135                 state->fp_abi = abiflags.fp_abi;
 136
 137         return 0;
 138 }
 139
 140 int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
 141                    struct arch_elf_state *state)
 142 {
 143         union {
 144                 struct elf32_hdr e32;
 145                 struct elf64_hdr e64;
 146         } *ehdr = _ehdr;
 147         union {
 148                 struct elf32_hdr e32;
 149                 struct elf64_hdr e64;
 150         } *iehdr = _interp_ehdr;
 151         struct mode_req prog_req, interp_req;
 152         int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
 153         bool elf32;
 154         u32 flags;
 155
 156         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
 157         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
 158
 159         /*
 160          * Determine the NaN personality, reject the binary if not allowed.
 161          * Also ensure that any interpreter matches the executable.
 162          */
 163         if (flags & EF_MIPS_NAN2008) {
 164                 if (mips_use_nan_2008)
 165                         state->nan_2008 = 1;
 166                 else
 167                         return -ENOEXEC;
 168         } else {
 169                 if (mips_use_nan_legacy)
 170                         state->nan_2008 = 0;
 171                 else
 172                         return -ENOEXEC;
 173         }
 174         if (has_interpreter) {
 175                 bool ielf32;
 176                 u32 iflags;
 177
 178                 ielf32 = iehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
 179                 iflags = ielf32 ? iehdr->e32.e_flags : iehdr->e64.e_flags;
 180
 181                 if ((flags ^ iflags) & EF_MIPS_NAN2008)
 182                         return -ELIBBAD;
 183         }
 184
 185         if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
 186                 return 0;
 187
 188         fp_abi = state->fp_abi;
 189
 190         if (has_interpreter) {
 191                 interp_fp_abi = state->interp_fp_abi;
 192
 193                 abi0 = min(fp_abi, interp_fp_abi);
 194                 abi1 = max(fp_abi, interp_fp_abi);
 195         } else {
 196                 abi0 = abi1 = fp_abi;
 197         }
 198
 199         if (elf32 && !(flags & EF_MIPS_ABI2)) {
 200                 /* Default to a mode capable of running code expecting FR=0 */
 201                 state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
 202
 203                 /* Allow all ABIs we know about */
 204                 max_abi = MIPS_ABI_FP_64A;
 205         } else {
 206                 /* MIPS64 code always uses FR=1, thus the default is easy */
 207                 state->overall_fp_mode = FP_FR1;
 208
 209                 /* Disallow access to the various FPXX & FP64 ABIs */
 210                 max_abi = MIPS_ABI_FP_SOFT;
 211         }
 212
 213         if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
 214             (abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
 215                 return -ELIBBAD;
 216
 217         /* It's time to determine the FPU mode requirements */
 218         prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
 219         interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
 220
 221         /*
 222          * Check whether the program's and interp's ABIs have a matching FPU
 223          * mode requirement.
 224          */
 225         prog_req.single = interp_req.single && prog_req.single;
 226         prog_req.soft = interp_req.soft && prog_req.soft;
 227         prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
 228         prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
 229         prog_req.fre = interp_req.fre && prog_req.fre;
 230
 231         /*
 232          * Determine the desired FPU mode
 233          *
 234          * Decision making:
 235          *
 236          * - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
 237          *   means that we have a combination of program and interpreter
 238          *   that inherently require the hybrid FP mode.
 239          * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
 240          *   fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
 241          *   instructions so we don't care about the mode. We will simply use
 242          *   the one preferred by the hardware. In fpxx case, that ABI can
 243          *   handle both FR=1 and FR=0, so, again, we simply choose the one
 244          *   preferred by the hardware. Next, if we only use single-precision
 245          *   FPU instructions, and the default ABI FPU mode is not good
 246          *   (ie single + any ABI combination), we set again the FPU mode to the
 247          *   one is preferred by the hardware. Next, if we know that the code
 248          *   will only use single-precision instructions, shown by single being
 249          *   true but frdefault being false, then we again set the FPU mode to
 250          *   the one that is preferred by the hardware.
 251          * - We want FP_FR1 if that's the only matching mode and the default one
 252          *   is not good.
 253          * - Return with -ELIBADD if we can't find a matching FPU mode.
 254          */
 255         if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
 256                 state->overall_fp_mode = FP_FRE;
 257         else if ((prog_req.fr1 && prog_req.frdefault) ||
 258                  (prog_req.single && !prog_req.frdefault))
 259                 /* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
 260                 state->overall_fp_mode = ((current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
 261                                           cpu_has_mips_r2_r6) ?
 262                                           FP_FR1 : FP_FR0;
 263         else if (prog_req.fr1)
 264                 state->overall_fp_mode = FP_FR1;
 265         else  if (!prog_req.fre && !prog_req.frdefault &&
 266                   !prog_req.fr1 && !prog_req.single && !prog_req.soft)
 267                 return -ELIBBAD;
 268
 269         return 0;
 270 }
 271
 272 static inline void set_thread_fp_mode(int hybrid, int regs32)
 273 {
 274         if (hybrid)
 275                 set_thread_flag(TIF_HYBRID_FPREGS);
 276         else
 277                 clear_thread_flag(TIF_HYBRID_FPREGS);
 278         if (regs32)
 279                 set_thread_flag(TIF_32BIT_FPREGS);
 280         else
 281                 clear_thread_flag(TIF_32BIT_FPREGS);
 282 }
 283
 284 void mips_set_personality_fp(struct arch_elf_state *state)
 285 {
 286         /*
 287          * This function is only ever called for O32 ELFs so we should
 288          * not be worried about N32/N64 binaries.
 289          */
 290
 291         if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
 292                 return;
 293
 294         switch (state->overall_fp_mode) {
 295         case FP_FRE:
 296                 set_thread_fp_mode(1, 0);
 297                 break;
 298         case FP_FR0:
 299                 set_thread_fp_mode(0, 1);
 300                 break;
 301         case FP_FR1:
 302                 set_thread_fp_mode(0, 0);
 303                 break;
 304         default:
 305                 BUG();
 306         }
 307 }
 308
 309 /*
 310  * Select the IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode
 311  * in FCSR according to the ELF NaN personality.
 312  */
 313 void mips_set_personality_nan(struct arch_elf_state *state)
 314 {
 315         struct cpuinfo_mips *c = &boot_cpu_data;
 316         struct task_struct *t = current;
 317
 318         t->thread.fpu.fcr31 = c->fpu_csr31;
 319         switch (state->nan_2008) {
 320         case 0:
 321                 break;
 322         case 1:
 323                 if (!(c->fpu_msk31 & FPU_CSR_NAN2008))
 324                         t->thread.fpu.fcr31 |= FPU_CSR_NAN2008;
 325                 if (!(c->fpu_msk31 & FPU_CSR_ABS2008))
 326                         t->thread.fpu.fcr31 |= FPU_CSR_ABS2008;
 327                 break;
 328         default:
 329                 BUG();
 330         }
 331 }
 332
 333 int mips_elf_read_implies_exec(void *elf_ex, int exstack)
 334 {
 335         if (exstack != EXSTACK_DISABLE_X) {
 336                 /* The binary doesn't request a non-executable stack */
 337                 return 1;
 338         }
 339
 340         if (!cpu_has_rixi) {
 341                 /* The CPU doesn't support non-executable memory */
 342                 return 1;
 343         }
 344
 345         return 0;
 346 }
 347 EXPORT_SYMBOL(mips_elf_read_implies_exec);