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         struct elf32_hdr *ehdr32 = _ehdr;
  72         struct elf32_phdr *phdr32 = _phdr;
  73         struct elf64_phdr *phdr64 = _phdr;
  74         struct mips_elf_abiflags_v0 abiflags;
  75         int ret;
  76
  77         /* Lets see if this is an O32 ELF */
  78         if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
  79                 if (ehdr32->e_flags & EF_MIPS_FP64) {
  80                         /*
  81                          * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
  82                          * later if needed
  83                          */
  84                         if (is_interp)
  85                                 state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
  86                         else
  87                                 state->fp_abi = MIPS_ABI_FP_OLD_64;
  88                 }
  89                 if (phdr32->p_type != PT_MIPS_ABIFLAGS)
  90                         return 0;
  91
  92                 if (phdr32->p_filesz < sizeof(abiflags))
  93                         return -EINVAL;
  94
  95                 ret = kernel_read(elf, phdr32->p_offset,
  96                                   (char *)&abiflags,
  97                                   sizeof(abiflags));
  98         } else {
  99                 if (phdr64->p_type != PT_MIPS_ABIFLAGS)
 100                         return 0;
 101                 if (phdr64->p_filesz < sizeof(abiflags))
 102                         return -EINVAL;
 103
 104                 ret = kernel_read(elf, phdr64->p_offset,
 105                                   (char *)&abiflags,
 106                                   sizeof(abiflags));
 107         }
 108
 109         if (ret < 0)
 110                 return ret;
 111         if (ret != sizeof(abiflags))
 112                 return -EIO;
 113
 114         /* Record the required FP ABIs for use by mips_check_elf */
 115         if (is_interp)
 116                 state->interp_fp_abi = abiflags.fp_abi;
 117         else
 118                 state->fp_abi = abiflags.fp_abi;
 119
 120         return 0;
 121 }
 122
 123 int arch_check_elf(void *_ehdr, bool has_interpreter,
 124                    struct arch_elf_state *state)
 125 {
 126         struct elf32_hdr *ehdr = _ehdr;
 127         struct mode_req prog_req, interp_req;
 128         int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
 129         bool is_mips64;
 130
 131         if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
 132                 return 0;
 133
 134         fp_abi = state->fp_abi;
 135
 136         if (has_interpreter) {
 137                 interp_fp_abi = state->interp_fp_abi;
 138
 139                 abi0 = min(fp_abi, interp_fp_abi);
 140                 abi1 = max(fp_abi, interp_fp_abi);
 141         } else {
 142                 abi0 = abi1 = fp_abi;
 143         }
 144
 145         is_mips64 = (ehdr->e_ident[EI_CLASS] == ELFCLASS64) ||
 146                     (ehdr->e_flags & EF_MIPS_ABI2);
 147
 148         if (is_mips64) {
 149                 /* MIPS64 code always uses FR=1, thus the default is easy */
 150                 state->overall_fp_mode = FP_FR1;
 151
 152                 /* Disallow access to the various FPXX & FP64 ABIs */
 153                 max_abi = MIPS_ABI_FP_SOFT;
 154         } else {
 155                 /* Default to a mode capable of running code expecting FR=0 */
 156                 state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
 157
 158                 /* Allow all ABIs we know about */
 159                 max_abi = MIPS_ABI_FP_64A;
 160         }
 161
 162         if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
 163             (abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
 164                 return -ELIBBAD;
 165
 166         /* It's time to determine the FPU mode requirements */
 167         prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
 168         interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
 169
 170         /*
 171          * Check whether the program's and interp's ABIs have a matching FPU
 172          * mode requirement.
 173          */
 174         prog_req.single = interp_req.single && prog_req.single;
 175         prog_req.soft = interp_req.soft && prog_req.soft;
 176         prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
 177         prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
 178         prog_req.fre = interp_req.fre && prog_req.fre;
 179
 180         /*
 181          * Determine the desired FPU mode
 182          *
 183          * Decision making:
 184          *
 185          * - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
 186          *   means that we have a combination of program and interpreter
 187          *   that inherently require the hybrid FP mode.
 188          * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
 189          *   fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
 190          *   instructions so we don't care about the mode. We will simply use
 191          *   the one preferred by the hardware. In fpxx case, that ABI can
 192          *   handle both FR=1 and FR=0, so, again, we simply choose the one
 193          *   preferred by the hardware. Next, if we only use single-precision
 194          *   FPU instructions, and the default ABI FPU mode is not good
 195          *   (ie single + any ABI combination), we set again the FPU mode to the
 196          *   one is preferred by the hardware. Next, if we know that the code
 197          *   will only use single-precision instructions, shown by single being
 198          *   true but frdefault being false, then we again set the FPU mode to
 199          *   the one that is preferred by the hardware.
 200          * - We want FP_FR1 if that's the only matching mode and the default one
 201          *   is not good.
 202          * - Return with -ELIBADD if we can't find a matching FPU mode.
 203          */
 204         if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
 205                 state->overall_fp_mode = FP_FRE;
 206         else if ((prog_req.fr1 && prog_req.frdefault) ||
 207                  (prog_req.single && !prog_req.frdefault))
 208                 /* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
 209                 state->overall_fp_mode = ((current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
 210                                           cpu_has_mips_r2_r6) ?
 211                                           FP_FR1 : FP_FR0;
 212         else if (prog_req.fr1)
 213                 state->overall_fp_mode = FP_FR1;
 214         else  if (!prog_req.fre && !prog_req.frdefault &&
 215                   !prog_req.fr1 && !prog_req.single && !prog_req.soft)
 216                 return -ELIBBAD;
 217
 218         return 0;
 219 }
 220
 221 static inline void set_thread_fp_mode(int hybrid, int regs32)
 222 {
 223         if (hybrid)
 224                 set_thread_flag(TIF_HYBRID_FPREGS);
 225         else
 226                 clear_thread_flag(TIF_HYBRID_FPREGS);
 227         if (regs32)
 228                 set_thread_flag(TIF_32BIT_FPREGS);
 229         else
 230                 clear_thread_flag(TIF_32BIT_FPREGS);
 231 }
 232
 233 void mips_set_personality_fp(struct arch_elf_state *state)
 234 {
 235         /*
 236          * This function is only ever called for O32 ELFs so we should
 237          * not be worried about N32/N64 binaries.
 238          */
 239
 240         if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
 241                 return;
 242
 243         switch (state->overall_fp_mode) {
 244         case FP_FRE:
 245                 set_thread_fp_mode(1, 0);
 246                 break;
 247         case FP_FR0:
 248                 set_thread_fp_mode(0, 1);
 249                 break;
 250         case FP_FR1:
 251                 set_thread_fp_mode(0, 0);
 252                 break;
 253         default:
 254                 BUG();
 255         }
 256 }