sysdeps/mips/dl-machine-reject-phdr.h

   1 /* Machine-dependent program header inspection for the ELF loader.
   2    Copyright (C) 2014-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _DL_MACHINE_REJECT_PHDR_H
  20 #define _DL_MACHINE_REJECT_PHDR_H 1
  21
  22 #include <unistd.h>
  23 #include <sys/prctl.h>
  24
  25 #if defined PR_GET_FP_MODE && defined PR_SET_FP_MODE
  26 # define HAVE_PRCTL_FP_MODE 1
  27 #else
  28 # define HAVE_PRCTL_FP_MODE 0
  29 #endif
  30
  31 /* Reject an object with a debug message.  */
  32 #define REJECT(str, args...)                                                  \
  33   {                                                                           \
  34     if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))               \
  35       _dl_debug_printf (str, ##args);                                         \
  36     return true;                                                              \
  37   }
  38
  39 /* Search the program headers for the ABI Flags.  */
  40
  41 static inline const ElfW(Phdr) *
  42 find_mips_abiflags (const ElfW(Phdr) *phdr, ElfW(Half) phnum)
  43 {
  44   const ElfW(Phdr) *ph;
  45
  46   for (ph = phdr; ph < &phdr[phnum]; ++ph)
  47     if (ph->p_type == PT_MIPS_ABIFLAGS)
  48       return ph;
  49   return NULL;
  50 }
  51
  52 /* Cache the FP ABI value from the PT_MIPS_ABIFLAGS program header.  */
  53
  54 static bool
  55 cached_fpabi_reject_phdr_p (struct link_map *l)
  56 {
  57   if (l->l_mach.fpabi == 0)
  58     {
  59       const ElfW(Phdr) *ph = find_mips_abiflags (l->l_phdr, l->l_phnum);
  60
  61       if (ph)
  62         {
  63           Elf_MIPS_ABIFlags_v0 * mips_abiflags;
  64           if (ph->p_filesz < sizeof (Elf_MIPS_ABIFlags_v0))
  65             REJECT ("   %s: malformed PT_MIPS_ABIFLAGS found\n", l->l_name);
  66
  67           mips_abiflags = (Elf_MIPS_ABIFlags_v0 *) (l->l_addr + ph->p_vaddr);
  68
  69           if (__glibc_unlikely (mips_abiflags->flags2 != 0))
  70             REJECT ("   %s: unknown MIPS.abiflags flags2: %u\n", l->l_name,
  71                     mips_abiflags->flags2);
  72
  73           l->l_mach.fpabi = mips_abiflags->fp_abi;
  74           l->l_mach.odd_spreg = (mips_abiflags->flags1
  75                                  & MIPS_AFL_FLAGS1_ODDSPREG) != 0;
  76         }
  77       else
  78         {
  79           l->l_mach.fpabi = -1;
  80           l->l_mach.odd_spreg = true;
  81         }
  82     }
  83   return false;
  84 }
  85
  86 /* Return a description of the specified floating-point ABI.  */
  87
  88 static const char *
  89 fpabi_string (int fpabi)
  90 {
  91   switch (fpabi)
  92     {
  93     case Val_GNU_MIPS_ABI_FP_ANY:
  94       return "Hard or soft float";
  95     case Val_GNU_MIPS_ABI_FP_DOUBLE:
  96       return "Hard float (double precision)";
  97     case Val_GNU_MIPS_ABI_FP_SINGLE:
  98       return "Hard float (single precision)";
  99     case Val_GNU_MIPS_ABI_FP_SOFT:
 100       return "Soft float";
 101     case Val_GNU_MIPS_ABI_FP_OLD_64:
 102       return "Unsupported FP64";
 103     case Val_GNU_MIPS_ABI_FP_XX:
 104       return "Hard float (32-bit CPU, Any FPU)";
 105     case Val_GNU_MIPS_ABI_FP_64:
 106       return "Hard float (32-bit CPU, 64-bit FPU)";
 107     case Val_GNU_MIPS_ABI_FP_64A:
 108       return "Hard float compat (32-bit CPU, 64-bit FPU)";
 109     case -1:
 110       return "Double precision, single precision or soft float";
 111     default:
 112       return "Unknown FP ABI";
 113     }
 114 }
 115
 116 /* A structure to describe the requirements of each FP ABI extension.
 117    Each field says whether the ABI can be executed in that mode.  The FR0 field
 118    is actually overloaded and means 'default' FR mode for the ABI.  I.e. For
 119    O32 it is FR0 and for N32/N64 it is actually FR1.  Since this logic is
 120    focussed on the intricacies of mode management for O32 we call the field
 121    FR0.  */
 122
 123 struct abi_req
 124 {
 125   bool single;
 126   bool soft;
 127   bool fr0;
 128   bool fr1;
 129   bool fre;
 130 };
 131
 132 /* FP ABI requirements for all Val_GNU_MIPS_ABI_FP_* values.  */
 133
 134 static const struct abi_req reqs[Val_GNU_MIPS_ABI_FP_MAX + 1] =
 135     {{true,  true,  true,  true,  true},  /* Any */
 136      {false, false, true,  false, true},  /* Double-float */
 137      {true,  false, false, false, false}, /* Single-float */
 138      {false, true,  false, false, false}, /* Soft-float */
 139      {false, false, false, false, false}, /* old-FP64 */
 140      {false, false, true,  true,  true},  /* FPXX */
 141      {false, false, false, true,  false}, /* FP64 */
 142      {false, false, false, true,  true}}; /* FP64A */
 143
 144 /* FP ABI requirements for objects without a PT_MIPS_ABIFLAGS segment.  */
 145
 146 static const struct abi_req none_req = { true, true, true, false, true };
 147
 148 /* Return true iff ELF program headers are incompatible with the running
 149    host.  This verifies that floating-point ABIs are compatible and
 150    re-configures the hardware mode if necessary.  This code handles both the
 151    DT_NEEDED libraries and the dlopen'ed libraries.  It also accounts for the
 152    impact of dlclose.  */
 153
 154 static bool __attribute_used__
 155 elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, unsigned int phnum,
 156                            const char *buf, size_t len, struct link_map *map,
 157                            int fd)
 158 {
 159   const ElfW(Phdr) *ph = find_mips_abiflags (phdr, phnum);
 160   struct link_map *l;
 161   Lmid_t nsid;
 162   int in_abi = -1;
 163   struct abi_req in_req;
 164   Elf_MIPS_ABIFlags_v0 mips_abiflags;
 165   bool perfect_match = false;
 166 #if _MIPS_SIM == _ABIO32
 167   unsigned int cur_mode = -1;
 168 # if HAVE_PRCTL_FP_MODE
 169   bool cannot_mode_switch = false;
 170
 171   /* Get the current hardware mode.  */
 172   cur_mode = __prctl (PR_GET_FP_MODE);
 173 # endif
 174 #endif
 175
 176   /* Read the attributes section.  */
 177   if (ph != NULL)
 178     {
 179       ElfW(Addr) size = sizeof (Elf_MIPS_ABIFlags_v0);
 180
 181       if (ph->p_filesz < size)
 182         REJECT ("   contains malformed PT_MIPS_ABIFLAGS\n");
 183
 184       __lseek (fd, ph->p_offset, SEEK_SET);
 185       if (__libc_read (fd, (void *) &mips_abiflags, size) != size)
 186         REJECT ("   unable to read PT_MIPS_ABIFLAGS\n");
 187
 188       if (__glibc_unlikely (mips_abiflags.flags2 != 0))
 189         REJECT ("   unknown MIPS.abiflags flags2: %u\n", mips_abiflags.flags2);
 190
 191       in_abi = mips_abiflags.fp_abi;
 192     }
 193
 194   /* ANY is compatible with anything.  */
 195   perfect_match |= (in_abi == Val_GNU_MIPS_ABI_FP_ANY);
 196
 197   /* Unknown ABIs are rejected.  */
 198   if (in_abi != -1 && in_abi > Val_GNU_MIPS_ABI_FP_MAX)
 199     REJECT ("   uses unknown FP ABI: %u\n", in_abi);
 200
 201   /* Obtain the initial requirements.  */
 202   in_req = (in_abi == -1) ? none_req : reqs[in_abi];
 203
 204   /* Check that the new requirement does not conflict with any currently
 205      loaded object.  */
 206   for (nsid = 0; nsid < DL_NNS; ++nsid)
 207     for (l = GL(dl_ns)[nsid]._ns_loaded; l != NULL; l = l->l_next)
 208       {
 209         struct abi_req existing_req;
 210
 211         if (cached_fpabi_reject_phdr_p (l))
 212           return true;
 213
 214 #if _MIPS_SIM == _ABIO32
 215         /* A special case arises for O32 FP64 and FP64A where the kernel
 216            pre-dates PT_MIPS_ABIFLAGS.  These ABIs will be blindly loaded even
 217            if the hardware mode is unavailable or disabled.  In this
 218            circumstance the prctl call to obtain the current mode will fail.
 219            Detect this situation here and reject everything.  This will
 220            effectively prevent dynamically linked applications from failing in
 221            unusual ways but there is nothing we can do to help static
 222            applications.  */
 223         if ((l->l_mach.fpabi == Val_GNU_MIPS_ABI_FP_64A
 224              || l->l_mach.fpabi == Val_GNU_MIPS_ABI_FP_64)
 225             && cur_mode == -1)
 226           REJECT ("   found %s running in the wrong mode\n",
 227                   fpabi_string (l->l_mach.fpabi));
 228 #endif
 229
 230         /* Found a perfect match, success.  */
 231         perfect_match |= (in_abi == l->l_mach.fpabi);
 232
 233         /* Unknown ABIs are rejected.  */
 234         if (l->l_mach.fpabi != -1 && l->l_mach.fpabi > Val_GNU_MIPS_ABI_FP_MAX)
 235           REJECT ("   found unknown FP ABI: %u\n", l->l_mach.fpabi);
 236
 237         existing_req = (l->l_mach.fpabi == -1 ? none_req
 238                         : reqs[l->l_mach.fpabi]);
 239
 240         /* Merge requirements.  */
 241         in_req.soft &= existing_req.soft;
 242         in_req.single &= existing_req.single;
 243         in_req.fr0 &= existing_req.fr0;
 244         in_req.fr1 &= existing_req.fr1;
 245         in_req.fre &= existing_req.fre;
 246
 247         /* If there is at least one mode which is still usable then the new
 248            object can be loaded.  */
 249         if (in_req.single || in_req.soft || in_req.fr1 || in_req.fr0
 250             || in_req.fre)
 251           {
 252 #if _MIPS_SIM == _ABIO32 && HAVE_PRCTL_FP_MODE
 253             /* Account for loaded ABIs which prohibit mode switching.  */
 254             if (l->l_mach.fpabi == Val_GNU_MIPS_ABI_FP_XX)
 255               cannot_mode_switch |= l->l_mach.odd_spreg;
 256 #endif
 257           }
 258         else
 259           REJECT ("   uses %s, already loaded %s\n",
 260                   fpabi_string (in_abi),
 261                   fpabi_string (l->l_mach.fpabi));
 262       }
 263
 264 #if _MIPS_SIM == _ABIO32
 265   /* At this point we know that the newly loaded object is compatible with all
 266      existing objects but the hardware mode may not be correct.  */
 267   if ((in_req.fr1 || in_req.fre || in_req.fr0)
 268       && !perfect_match)
 269     {
 270       if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
 271         _dl_debug_printf ("   needs %s%s mode\n", in_req.fr0 ? "FR0 or " : "",
 272                           (in_req.fre && !in_req.fr1) ? "FRE" : "FR1");
 273
 274       /* If the PR_GET_FP_MODE is not supported then only FR0 is available.
 275          If the overall requirements cannot be met by FR0 then reject the
 276          object.  */
 277       if (cur_mode == -1)
 278         return !in_req.fr0;
 279
 280 # if HAVE_PRCTL_FP_MODE
 281       {
 282         unsigned int fr1_mode = PR_FP_MODE_FR;
 283
 284         /* It is not possible to change the mode of a thread which may be
 285            executing FPXX code with odd-singles.  If an FPXX object with
 286            odd-singles is loaded then just check the current mode is OK. This
 287            can be either the FR1 mode or FR0 if the requirements are met by
 288            FR0.  */
 289         if (cannot_mode_switch)
 290           return (!(in_req.fre && cur_mode == (PR_FP_MODE_FR | PR_FP_MODE_FRE))
 291                   && !(in_req.fr1 && cur_mode == PR_FP_MODE_FR)
 292                   && !(in_req.fr0 && cur_mode == 0));
 293
 294         /* If the overall requirements can be satisfied by FRE but not FR1 then
 295            fr1_mode must become FRE.  */
 296         if (in_req.fre && !in_req.fr1)
 297           fr1_mode |= PR_FP_MODE_FRE;
 298
 299         /* Set the new mode.  Use fr1_mode if the requirements cannot be met by
 300            FR0.  */
 301         if (!in_req.fr0)
 302           return __prctl (PR_SET_FP_MODE, fr1_mode) != 0;
 303         else if (__prctl (PR_SET_FP_MODE, /* fr0_mode */ 0) != 0)
 304           {
 305             /* Setting FR0 can validly fail on an R6 core so retry with the FR1
 306                mode as a fall back.  */
 307             if (errno != ENOTSUP)
 308               return true;
 309
 310             return __prctl (PR_SET_FP_MODE, fr1_mode) != 0;
 311           }
 312       }
 313 # endif /* HAVE_PRCTL_FP_MODE */
 314     }
 315 #endif /* _MIPS_SIM == _ABIO32 */
 316
 317   return false;
 318 }
 319
 320 #endif /* dl-machine-reject-phdr.h */