LXR linux/arch/x86/kernel/static

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/static_call.h>
   3#include <linux/memory.h>
   4#include <linux/bug.h>
   5#include <asm/text-patching.h>
   6
   7enum insn_type {
   8        CALL = 0, /* site call */
   9        NOP = 1,  /* site cond-call */
  10        JMP = 2,  /* tramp / site tail-call */
  11        RET = 3,  /* tramp / site cond-tail-call */
  12};
  13
  14/*
  15 * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax
  16 * The REX.W cancels the effect of any data16.
  17 */
  18static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 };
  19
  20static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
  21
  22static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
  23{
  24        const void *emulate = NULL;
  25        int size = CALL_INSN_SIZE;
  26        const void *code;
  27
  28        switch (type) {
  29        case CALL:
  30                code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
  31                if (func == &__static_call_return0) {
  32                        emulate = code;
  33                        code = &xor5rax;
  34                }
  35
  36                break;
  37
  38        case NOP:
  39                code = x86_nops[5];
  40                break;
  41
  42        case JMP:
  43                code = text_gen_insn(JMP32_INSN_OPCODE, insn, func);
  44                break;
  45
  46        case RET:
  47                code = &retinsn;
  48                break;
  49        }
  50
  51        if (memcmp(insn, code, size) == 0)
  52                return;
  53
  54        if (unlikely(system_state == SYSTEM_BOOTING))
  55                return text_poke_early(insn, code, size);
  56
  57        text_poke_bp(insn, code, size, emulate);
  58}
  59
  60static void __static_call_validate(void *insn, bool tail, bool tramp)
  61{
  62        u8 opcode = *(u8 *)insn;
  63
  64        if (tramp && memcmp(insn+5, "SCT", 3)) {
  65                pr_err("trampoline signature fail");
  66                BUG();
  67        }
  68
  69        if (tail) {
  70                if (opcode == JMP32_INSN_OPCODE ||
  71                    opcode == RET_INSN_OPCODE)
  72                        return;
  73        } else {
  74                if (opcode == CALL_INSN_OPCODE ||
  75                    !memcmp(insn, x86_nops[5], 5) ||
  76                    !memcmp(insn, xor5rax, 5))
  77                        return;
  78        }
  79
  80        /*
  81         * If we ever trigger this, our text is corrupt, we'll probably not live long.
  82         */
  83        pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
  84        BUG();
  85}
  86
  87static inline enum insn_type __sc_insn(bool null, bool tail)
  88{
  89        /*
  90         * Encode the following table without branches:
  91         *
  92         *      tail    null    insn
  93         *      -----+-------+------
  94         *        0  |   0   |  CALL
  95         *        0  |   1   |  NOP
  96         *        1  |   0   |  JMP
  97         *        1  |   1   |  RET
  98         */
  99        return 2*tail + null;
 100}
 101
 102void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 103{
 104        mutex_lock(&text_mutex);
 105
 106        if (tramp) {
 107                __static_call_validate(tramp, true, true);
 108                __static_call_transform(tramp, __sc_insn(!func, true), func);
 109        }
 110
 111        if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
 112                __static_call_validate(site, tail, false);
 113                __static_call_transform(site, __sc_insn(!func, tail), func);
 114        }
 115
 116        mutex_unlock(&text_mutex);
 117}
 118EXPORT_SYMBOL_GPL(arch_static_call_transform);
 119