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/elf.h>
  12 #include <linux/sched.h>
  13
  14 /* FPU modes */
  15 enum {
  16         FP_FRE,
  17         FP_FR0,
  18         FP_FR1,
  19 };
  20
  21 /**
  22  * struct mode_req - ABI FPU mode requirements
  23  * @single:     The program being loaded needs an FPU but it will only issue
  24  *              single precision instructions meaning that it can execute in
  25  *              either FR0 or FR1.
  26  * @soft:       The soft(-float) requirement means that the program being
  27  *              loaded needs has no FPU dependency at all (i.e. it has no
  28  *              FPU instructions).
  29  * @fr1:        The program being loaded depends on FPU being in FR=1 mode.
  30  * @frdefault:  The program being loaded depends on the default FPU mode.
  31  *              That is FR0 for O32 and FR1 for N32/N64.
  32  * @fre:        The program being loaded depends on FPU with FRE=1. This mode is
  33  *              a bridge which uses FR=1 whilst still being able to maintain
  34  *              full compatibility with pre-existing code using the O32 FP32
  35  *              ABI.
  36  *
  37  * More information about the FP ABIs can be found here:
  38  *
  39  * https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
  40  *
  41  */
  42
  43 struct mode_req {
  44         bool single;
  45         bool soft;
  46         bool fr1;
  47         bool frdefault;
  48         bool fre;
  49 };
  50
  51 static const struct mode_req fpu_reqs[] = {
  52         [MIPS_ABI_FP_ANY]    = { true,  true,  true,  true,  true  },
  53         [MIPS_ABI_FP_DOUBLE] = { false, false, false, true,  true  },
  54         [MIPS_ABI_FP_SINGLE] = { true,  false, false, false, false },
  55         [MIPS_ABI_FP_SOFT]   = { false, true,  false, false, false },
  56         [MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
  57         [MIPS_ABI_FP_XX]     = { false, false, true,  true,  true  },
  58         [MIPS_ABI_FP_64]     = { false, false, true,  false, false },
  59         [MIPS_ABI_FP_64A]    = { false, false, true,  false, true  }
  60 };
  61
  62 /*
  63  * Mode requirements when .MIPS.abiflags is not present in the ELF.
  64  * Not present means that everything is acceptable except FR1.
  65  */
  66 static struct mode_req none_req = { true, true, false, true, true };
  67
  68 int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
  69                      bool is_interp, struct arch_elf_state *state)
  70 {
  71         union {
  72                 struct elf32_hdr e32;
  73                 struct elf64_hdr e64;
  74         } *ehdr = _ehdr;
  75         struct elf32_phdr *phdr32 = _phdr;
  76         struct elf64_phdr *phdr64 = _phdr;
  77         struct mips_elf_abiflags_v0 abiflags;
  78         bool elf32;
  79         u32 flags;
  80         int ret;
  81
  82         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
  83         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
  84
  85         /* Lets see if this is an O32 ELF */
  86         if (elf32) {
  87                 if (flags & EF_MIPS_FP64) {
  88                         /*
  89                          * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
  90                          * later if needed
  91                          */
  92                         if (is_interp)
  93                                 state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
  94                         else
  95                                 state->fp_abi = MIPS_ABI_FP_OLD_64;
  96                 }
  97                 if (phdr32->p_type != PT_MIPS_ABIFLAGS)
  98                         return 0;
  99
 100                 if (phdr32->p_filesz < sizeof(abiflags))
 101                         return -EINVAL;
 102
 103                 ret = kernel_read(elf, phdr32->p_offset,
 104                                   (char *)&abiflags,
 105                                   sizeof(abiflags));
 106         } else {
 107                 if (phdr64->p_type != PT_MIPS_ABIFLAGS)
 108                         return 0;
 109                 if (phdr64->p_filesz < sizeof(abiflags))
 110                         return -EINVAL;
 111
 112                 ret = kernel_read(elf, phdr64->p_offset,
 113                                   (char *)&abiflags,
 114                                   sizeof(abiflags));
 115         }
 116
 117         if (ret < 0)
 118                 return ret;
 119         if (ret != sizeof(abiflags))
 120                 return -EIO;
 121
 122         /* Record the required FP ABIs for use by mips_check_elf */
 123         if (is_interp)
 124                 state->interp_fp_abi = abiflags.fp_abi;
 125         else
 126                 state->fp_abi = abiflags.fp_abi;
 127
 128         return 0;
 129 }
 130
 131 int arch_check_elf(void *_ehdr, bool has_interpreter,
 132                    struct arch_elf_state *state)
 133 {
 134         union {
 135                 struct elf32_hdr e32;
 136                 struct elf64_hdr e64;
 137         } *ehdr = _ehdr;
 138         struct mode_req prog_req, interp_req;
 139         int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
 140         bool elf32;
 141         u32 flags;
 142
 143         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
 144         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
 145
 146         if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
 147                 return 0;
 148
 149         fp_abi = state->fp_abi;
 150
 151         if (has_interpreter) {
 152                 interp_fp_abi = state->interp_fp_abi;
 153
 154                 abi0 = min(fp_abi, interp_fp_abi);
 155                 abi1 = max(fp_abi, interp_fp_abi);
 156         } else {
 157                 abi0 = abi1 = fp_abi;
 158         }
 159
 160         if (elf32 && !(flags & EF_MIPS_ABI2)) {
 161                 /* Default to a mode capable of running code expecting FR=0 */
 162                 state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
 163
 164                 /* Allow all ABIs we know about */
 165                 max_abi = MIPS_ABI_FP_64A;
 166         } else {
 167                 /* MIPS64 code always uses FR=1, thus the default is easy */
 168                 state->overall_fp_mode = FP_FR1;
 169
 170                 /* Disallow access to the various FPXX & FP64 ABIs */
 171                 max_abi = MIPS_ABI_FP_SOFT;
 172         }
 173
 174         if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
 175             (abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
 176                 return -ELIBBAD;
 177
 178         /* It's time to determine the FPU mode requirements */
 179         prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
 180         interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
 181
 182         /*
 183          * Check whether the program's and interp's ABIs have a matching FPU
 184          * mode requirement.
 185          */
 186         prog_req.single = interp_req.single && prog_req.single;
 187         prog_req.soft = interp_req.soft && prog_req.soft;
 188         prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
 189         prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
 190         prog_req.fre = interp_req.fre && prog_req.fre;
 191
 192         /*
 193          * Determine the desired FPU mode
 194          *
 195          * Decision making:
 196          *
 197          * - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
 198          *   means that we have a combination of program and interpreter
 199          *   that inherently require the hybrid FP mode.
 200          * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
 201          *   fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
 202          *   instructions so we don't care about the mode. We will simply use
 203          *   the one preferred by the hardware. In fpxx case, that ABI can
 204          *   handle both FR=1 and FR=0, so, again, we simply choose the one
 205          *   preferred by the hardware. Next, if we only use single-precision
 206          *   FPU instructions, and the default ABI FPU mode is not good
 207          *   (ie single + any ABI combination), we set again the FPU mode to the
 208          *   one is preferred by the hardware. Next, if we know that the code
 209          *   will only use single-precision instructions, shown by single being
 210          *   true but frdefault being false, then we again set the FPU mode to
 211          *   the one that is preferred by the hardware.
 212          * - We want FP_FR1 if that's the only matching mode and the default one
 213          *   is not good.
 214          * - Return with -ELIBADD if we can't find a matching FPU mode.
 215          */
 216         if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
 217                 state->overall_fp_mode = FP_FRE;
 218         else if ((prog_req.fr1 && prog_req.frdefault) ||
 219                  (prog_req.single && !prog_req.frdefault))
 220                 /* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
 221                 state->overall_fp_mode = ((current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
 222                                           cpu_has_mips_r2_r6) ?
 223                                           FP_FR1 : FP_FR0;
 224         else if (prog_req.fr1)
 225                 state->overall_fp_mode = FP_FR1;
 226         else  if (!prog_req.fre && !prog_req.frdefault &&
 227                   !prog_req.fr1 && !prog_req.single && !prog_req.soft)
 228                 return -ELIBBAD;
 229
 230         return 0;
 231 }
 232
 233 static inline void set_thread_fp_mode(int hybrid, int regs32)
 234 {
 235         if (hybrid)
 236                 set_thread_flag(TIF_HYBRID_FPREGS);
 237         else
 238                 clear_thread_flag(TIF_HYBRID_FPREGS);
 239         if (regs32)
 240                 set_thread_flag(TIF_32BIT_FPREGS);
 241         else
 242                 clear_thread_flag(TIF_32BIT_FPREGS);
 243 }
 244
 245 void mips_set_personality_fp(struct arch_elf_state *state)
 246 {
 247         /*
 248          * This function is only ever called for O32 ELFs so we should
 249          * not be worried about N32/N64 binaries.
 250          */
 251
 252         if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
 253                 return;
 254
 255         switch (state->overall_fp_mode) {
 256         case FP_FRE:
 257                 set_thread_fp_mode(1, 0);
 258                 break;
 259         case FP_FR0:
 260                 set_thread_fp_mode(0, 1);
 261                 break;
 262         case FP_FR1:
 263                 set_thread_fp_mode(0, 0);
 264                 break;
 265         default:
 266                 BUG();
 267         }
 268 }