arch/x86/include/asm/nospec-branch.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2
   3 #ifndef __NOSPEC_BRANCH_H__
   4 #define __NOSPEC_BRANCH_H__
   5
   6 #include <asm/alternative.h>
   7 #include <asm/alternative-asm.h>
   8 #include <asm/cpufeature.h>
   9
  10 #ifdef __ASSEMBLY__
  11
  12 /*
  13  * These are the bare retpoline primitives for indirect jmp and call.
  14  * Do not use these directly; they only exist to make the ALTERNATIVE
  15  * invocation below less ugly.
  16  */
  17 .macro RETPOLINE_JMP reg:req
  18         call    .Ldo_rop_\@
  19 .Lspec_trap_\@:
  20         pause
  21         jmp     .Lspec_trap_\@
  22 .Ldo_rop_\@:
  23         mov     \reg, (%_ASM_SP)
  24         ret
  25 .endm
  26
  27 /*
  28  * This is a wrapper around RETPOLINE_JMP so the called function in reg
  29  * returns to the instruction after the macro.
  30  */
  31 .macro RETPOLINE_CALL reg:req
  32         jmp     .Ldo_call_\@
  33 .Ldo_retpoline_jmp_\@:
  34         RETPOLINE_JMP \reg
  35 .Ldo_call_\@:
  36         call    .Ldo_retpoline_jmp_\@
  37 .endm
  38
  39 /*
  40  * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
  41  * indirect jmp/call which may be susceptible to the Spectre variant 2
  42  * attack.
  43  */
  44 .macro JMP_NOSPEC reg:req
  45 #ifdef CONFIG_RETPOLINE
  46         ALTERNATIVE_2 __stringify(jmp *\reg),                           \
  47                 __stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE, \
  48                 __stringify(lfence; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
  49 #else
  50         jmp     *\reg
  51 #endif
  52 .endm
  53
  54 .macro CALL_NOSPEC reg:req
  55 #ifdef CONFIG_RETPOLINE
  56         ALTERNATIVE_2 __stringify(call *\reg),                          \
  57                 __stringify(RETPOLINE_CALL \reg), X86_FEATURE_RETPOLINE,\
  58                 __stringify(lfence; call *\reg), X86_FEATURE_RETPOLINE_AMD
  59 #else
  60         call    *\reg
  61 #endif
  62 .endm
  63
  64 #else /* __ASSEMBLY__ */
  65
  66 #if defined(CONFIG_X86_64) && defined(RETPOLINE)
  67
  68 /*
  69  * Since the inline asm uses the %V modifier which is only in newer GCC,
  70  * the 64-bit one is dependent on RETPOLINE not CONFIG_RETPOLINE.
  71  */
  72 # define CALL_NOSPEC                                            \
  73         ALTERNATIVE(                                            \
  74         "call *%[thunk_target]\n",                              \
  75         "call __x86_indirect_thunk_%V[thunk_target]\n",         \
  76         X86_FEATURE_RETPOLINE)
  77 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)
  78
  79 #elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
  80 /*
  81  * For i386 we use the original ret-equivalent retpoline, because
  82  * otherwise we'll run out of registers. We don't care about CET
  83  * here, anyway.
  84  */
  85 # define CALL_NOSPEC ALTERNATIVE("call *%[thunk_target]\n",     \
  86         "       jmp    904f;\n"                                 \
  87         "       .align 16\n"                                    \
  88         "901:   call   903f;\n"                                 \
  89         "902:   pause;\n"                                       \
  90         "       jmp    902b;\n"                                 \
  91         "       .align 16\n"                                    \
  92         "903:   addl   $4, %%esp;\n"                            \
  93         "       pushl  %[thunk_target];\n"                      \
  94         "       ret;\n"                                         \
  95         "       .align 16\n"                                    \
  96         "904:   call   901b;\n",                                \
  97         X86_FEATURE_RETPOLINE)
  98
  99 # define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
 100 #else /* No retpoline */
 101 # define CALL_NOSPEC "call *%[thunk_target]\n"
 102 # define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
 103 #endif
 104
 105 #endif /* __ASSEMBLY__ */
 106 #endif /* __NOSPEC_BRANCH_H__ */