root/arch/mips/kernel/elf.c

DEFINITIONS

1. arch_elf_pt_proc
2. arch_check_elf
3. set_thread_fp_mode
4. mips_set_personality_fp
5. mips_set_personality_nan
6. mips_elf_read_implies_exec

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2014 Imagination Technologies
   4  * Author: Paul Burton <paul.burton@mips.com>
   5  */
   6 
   7 #include <linux/binfmts.h>
   8 #include <linux/elf.h>
   9 #include <linux/export.h>
  10 #include <linux/sched.h>
  11 
  12 #include <asm/cpu-features.h>
  13 #include <asm/cpu-info.h>
  14 
  15 #ifdef CONFIG_MIPS_FP_SUPPORT
  16 
  17 /* Whether to accept legacy-NaN and 2008-NaN user binaries.  */
  18 bool mips_use_nan_legacy;
  19 bool mips_use_nan_2008;
  20 
  21 /* FPU modes */
  22 enum {
  23         FP_FRE,
  24         FP_FR0,
  25         FP_FR1,
  26 };
  27 
  28 /**
  29  * struct mode_req - ABI FPU mode requirements
  30  * @single:     The program being loaded needs an FPU but it will only issue
  31  *              single precision instructions meaning that it can execute in
  32  *              either FR0 or FR1.
  33  * @soft:       The soft(-float) requirement means that the program being
  34  *              loaded needs has no FPU dependency at all (i.e. it has no
  35  *              FPU instructions).
  36  * @fr1:        The program being loaded depends on FPU being in FR=1 mode.
  37  * @frdefault:  The program being loaded depends on the default FPU mode.
  38  *              That is FR0 for O32 and FR1 for N32/N64.
  39  * @fre:        The program being loaded depends on FPU with FRE=1. This mode is
  40  *              a bridge which uses FR=1 whilst still being able to maintain
  41  *              full compatibility with pre-existing code using the O32 FP32
  42  *              ABI.
  43  *
  44  * More information about the FP ABIs can be found here:
  45  *
  46  * https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
  47  *
  48  */
  49 
  50 struct mode_req {
  51         bool single;
  52         bool soft;
  53         bool fr1;
  54         bool frdefault;
  55         bool fre;
  56 };
  57 
  58 static const struct mode_req fpu_reqs[] = {
  59         [MIPS_ABI_FP_ANY]    = { true,  true,  true,  true,  true  },
  60         [MIPS_ABI_FP_DOUBLE] = { false, false, false, true,  true  },
  61         [MIPS_ABI_FP_SINGLE] = { true,  false, false, false, false },
  62         [MIPS_ABI_FP_SOFT]   = { false, true,  false, false, false },
  63         [MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
  64         [MIPS_ABI_FP_XX]     = { false, false, true,  true,  true  },
  65         [MIPS_ABI_FP_64]     = { false, false, true,  false, false },
  66         [MIPS_ABI_FP_64A]    = { false, false, true,  false, true  }
  67 };
  68 
  69 /*
  70  * Mode requirements when .MIPS.abiflags is not present in the ELF.
  71  * Not present means that everything is acceptable except FR1.
  72  */
  73 static struct mode_req none_req = { true, true, false, true, true };
  74 
  75 int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
  76                      bool is_interp, struct arch_elf_state *state)
  77 {
  78         union {
  79                 struct elf32_hdr e32;
  80                 struct elf64_hdr e64;
  81         } *ehdr = _ehdr;
  82         struct elf32_phdr *phdr32 = _phdr;
  83         struct elf64_phdr *phdr64 = _phdr;
  84         struct mips_elf_abiflags_v0 abiflags;
  85         bool elf32;
  86         u32 flags;
  87         int ret;
  88         loff_t pos;
  89 
  90         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
  91         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
  92 
  93         /* Let's see if this is an O32 ELF */
  94         if (elf32) {
  95                 if (flags & EF_MIPS_FP64) {
  96                         /*
  97                          * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
  98                          * later if needed
  99                          */
 100                         if (is_interp)
 101                                 state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
 102                         else
 103                                 state->fp_abi = MIPS_ABI_FP_OLD_64;
 104                 }
 105                 if (phdr32->p_type != PT_MIPS_ABIFLAGS)
 106                         return 0;
 107 
 108                 if (phdr32->p_filesz < sizeof(abiflags))
 109                         return -EINVAL;
 110                 pos = phdr32->p_offset;
 111         } else {
 112                 if (phdr64->p_type != PT_MIPS_ABIFLAGS)
 113                         return 0;
 114                 if (phdr64->p_filesz < sizeof(abiflags))
 115                         return -EINVAL;
 116                 pos = phdr64->p_offset;
 117         }
 118 
 119         ret = kernel_read(elf, &abiflags, sizeof(abiflags), &pos);
 120         if (ret < 0)
 121                 return ret;
 122         if (ret != sizeof(abiflags))
 123                 return -EIO;
 124 
 125         /* Record the required FP ABIs for use by mips_check_elf */
 126         if (is_interp)
 127                 state->interp_fp_abi = abiflags.fp_abi;
 128         else
 129                 state->fp_abi = abiflags.fp_abi;
 130 
 131         return 0;
 132 }
 133 
 134 int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
 135                    struct arch_elf_state *state)
 136 {
 137         union {
 138                 struct elf32_hdr e32;
 139                 struct elf64_hdr e64;
 140         } *ehdr = _ehdr;
 141         union {
 142                 struct elf32_hdr e32;
 143                 struct elf64_hdr e64;
 144         } *iehdr = _interp_ehdr;
 145         struct mode_req prog_req, interp_req;
 146         int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
 147         bool elf32;
 148         u32 flags;
 149 
 150         elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
 151         flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
 152 
 153         /*
 154          * Determine the NaN personality, reject the binary if not allowed.
 155          * Also ensure that any interpreter matches the executable.
 156          */
 157         if (flags & EF_MIPS_NAN2008) {
 158                 if (mips_use_nan_2008)
 159                         state->nan_2008 = 1;
 160                 else
 161                         return -ENOEXEC;
 162         } else {
 163                 if (mips_use_nan_legacy)
 164                         state->nan_2008 = 0;
 165                 else
 166                         return -ENOEXEC;
 167         }
 168         if (has_interpreter) {
 169                 bool ielf32;
 170                 u32 iflags;
 171 
 172                 ielf32 = iehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
 173                 iflags = ielf32 ? iehdr->e32.e_flags : iehdr->e64.e_flags;
 174 
 175                 if ((flags ^ iflags) & EF_MIPS_NAN2008)
 176                         return -ELIBBAD;
 177         }
 178 
 179         if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
 180                 return 0;
 181 
 182         fp_abi = state->fp_abi;
 183 
 184         if (has_interpreter) {
 185                 interp_fp_abi = state->interp_fp_abi;
 186 
 187                 abi0 = min(fp_abi, interp_fp_abi);
 188                 abi1 = max(fp_abi, interp_fp_abi);
 189         } else {
 190                 abi0 = abi1 = fp_abi;
 191         }
 192 
 193         if (elf32 && !(flags & EF_MIPS_ABI2)) {
 194                 /* Default to a mode capable of running code expecting FR=0 */
 195                 state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
 196 
 197                 /* Allow all ABIs we know about */
 198                 max_abi = MIPS_ABI_FP_64A;
 199         } else {
 200                 /* MIPS64 code always uses FR=1, thus the default is easy */
 201                 state->overall_fp_mode = FP_FR1;
 202 
 203                 /* Disallow access to the various FPXX & FP64 ABIs */
 204                 max_abi = MIPS_ABI_FP_SOFT;
 205         }
 206 
 207         if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
 208             (abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
 209                 return -ELIBBAD;
 210 
 211         /* It's time to determine the FPU mode requirements */
 212         prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
 213         interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
 214 
 215         /*
 216          * Check whether the program's and interp's ABIs have a matching FPU
 217          * mode requirement.
 218          */
 219         prog_req.single = interp_req.single && prog_req.single;
 220         prog_req.soft = interp_req.soft && prog_req.soft;
 221         prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
 222         prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
 223         prog_req.fre = interp_req.fre && prog_req.fre;
 224 
 225         /*
 226          * Determine the desired FPU mode
 227          *
 228          * Decision making:
 229          *
 230          * - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
 231          *   means that we have a combination of program and interpreter
 232          *   that inherently require the hybrid FP mode.
 233          * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
 234          *   fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
 235          *   instructions so we don't care about the mode. We will simply use
 236          *   the one preferred by the hardware. In fpxx case, that ABI can
 237          *   handle both FR=1 and FR=0, so, again, we simply choose the one
 238          *   preferred by the hardware. Next, if we only use single-precision
 239          *   FPU instructions, and the default ABI FPU mode is not good
 240          *   (ie single + any ABI combination), we set again the FPU mode to the
 241          *   one is preferred by the hardware. Next, if we know that the code
 242          *   will only use single-precision instructions, shown by single being
 243          *   true but frdefault being false, then we again set the FPU mode to
 244          *   the one that is preferred by the hardware.
 245          * - We want FP_FR1 if that's the only matching mode and the default one
 246          *   is not good.
 247          * - Return with -ELIBADD if we can't find a matching FPU mode.
 248          */
 249         if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
 250                 state->overall_fp_mode = FP_FRE;
 251         else if ((prog_req.fr1 && prog_req.frdefault) ||
 252                  (prog_req.single && !prog_req.frdefault))
 253                 /* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
 254                 state->overall_fp_mode = ((raw_current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
 255                                           cpu_has_mips_r2_r6) ?
 256                                           FP_FR1 : FP_FR0;
 257         else if (prog_req.fr1)
 258                 state->overall_fp_mode = FP_FR1;
 259         else  if (!prog_req.fre && !prog_req.frdefault &&
 260                   !prog_req.fr1 && !prog_req.single && !prog_req.soft)
 261                 return -ELIBBAD;
 262 
 263         return 0;
 264 }
 265 
 266 static inline void set_thread_fp_mode(int hybrid, int regs32)
 267 {
 268         if (hybrid)
 269                 set_thread_flag(TIF_HYBRID_FPREGS);
 270         else
 271                 clear_thread_flag(TIF_HYBRID_FPREGS);
 272         if (regs32)
 273                 set_thread_flag(TIF_32BIT_FPREGS);
 274         else
 275                 clear_thread_flag(TIF_32BIT_FPREGS);
 276 }
 277 
 278 void mips_set_personality_fp(struct arch_elf_state *state)
 279 {
 280         /*
 281          * This function is only ever called for O32 ELFs so we should
 282          * not be worried about N32/N64 binaries.
 283          */
 284 
 285         if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
 286                 return;
 287 
 288         switch (state->overall_fp_mode) {
 289         case FP_FRE:
 290                 set_thread_fp_mode(1, 0);
 291                 break;
 292         case FP_FR0:
 293                 set_thread_fp_mode(0, 1);
 294                 break;
 295         case FP_FR1:
 296                 set_thread_fp_mode(0, 0);
 297                 break;
 298         default:
 299                 BUG();
 300         }
 301 }
 302 
 303 /*
 304  * Select the IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode
 305  * in FCSR according to the ELF NaN personality.
 306  */
 307 void mips_set_personality_nan(struct arch_elf_state *state)
 308 {
 309         struct cpuinfo_mips *c = &boot_cpu_data;
 310         struct task_struct *t = current;
 311 
 312         t->thread.fpu.fcr31 = c->fpu_csr31;
 313         switch (state->nan_2008) {
 314         case 0:
 315                 break;
 316         case 1:
 317                 if (!(c->fpu_msk31 & FPU_CSR_NAN2008))
 318                         t->thread.fpu.fcr31 |= FPU_CSR_NAN2008;
 319                 if (!(c->fpu_msk31 & FPU_CSR_ABS2008))
 320                         t->thread.fpu.fcr31 |= FPU_CSR_ABS2008;
 321                 break;
 322         default:
 323                 BUG();
 324         }
 325 }
 326 
 327 #endif /* CONFIG_MIPS_FP_SUPPORT */
 328 
 329 int mips_elf_read_implies_exec(void *elf_ex, int exstack)
 330 {
 331         if (exstack != EXSTACK_DISABLE_X) {
 332                 /* The binary doesn't request a non-executable stack */
 333                 return 1;
 334         }
 335 
 336         if (!cpu_has_rixi) {
 337                 /* The CPU doesn't support non-executable memory */
 338                 return 1;
 339         }
 340 
 341         return 0;
 342 }
 343 EXPORT_SYMBOL(mips_elf_read_implies_exec);