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Linux/arch/mips/kernel/elf.c

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  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);
348 

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