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 * cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax
  16 */
  17static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 };
  18
  19static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
  20
  21static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
  22{
  23        const void *emulate = NULL;
  24        int size = CALL_INSN_SIZE;
  25        const void *code;
  26
  27        switch (type) {
  28        case CALL:
  29                code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
  30                if (func == &__static_call_return0) {
  31                        emulate = code;
  32                        code = &xor5rax;
  33                }
  34
  35                break;
  36
  37        case NOP:
  38                code = x86_nops[5];
  39                break;
  40
  41        case JMP:
  42                code = text_gen_insn(JMP32_INSN_OPCODE, insn, func);
  43                break;
  44
  45        case RET:
  46                code = &retinsn;
  47                break;
  48        }
  49
  50        if (memcmp(insn, code, size) == 0)
  51                return;
  52
  53        if (unlikely(system_state == SYSTEM_BOOTING))
  54                return text_poke_early(insn, code, size);
  55
  56        text_poke_bp(insn, code, size, emulate);
  57}
  58
  59static void __static_call_validate(void *insn, bool tail, bool tramp)
  60{
  61        u8 opcode = *(u8 *)insn;
  62
  63        if (tramp && memcmp(insn+5, "SCT", 3)) {
  64                pr_err("trampoline signature fail");
  65                BUG();
  66        }
  67
  68        if (tail) {
  69                if (opcode == JMP32_INSN_OPCODE ||
  70                    opcode == RET_INSN_OPCODE)
  71                        return;
  72        } else {
  73                if (opcode == CALL_INSN_OPCODE ||
  74                    !memcmp(insn, x86_nops[5], 5) ||
  75                    !memcmp(insn, xor5rax, 5))
  76                        return;
  77        }
  78
  79        /*
  80         * If we ever trigger this, our text is corrupt, we'll probably not live long.
  81         */
  82        pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
  83        BUG();
  84}
  85
  86static inline enum insn_type __sc_insn(bool null, bool tail)
  87{
  88        /*
  89         * Encode the following table without branches:
  90         *
  91         *      tail    null    insn
  92         *      -----+-------+------
  93         *        0  |   0   |  CALL
  94         *        0  |   1   |  NOP
  95         *        1  |   0   |  JMP
  96         *        1  |   1   |  RET
  97         */
  98        return 2*tail + null;
  99}
 100
 101void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 102{
 103        mutex_lock(&text_mutex);
 104
 105        if (tramp) {
 106                __static_call_validate(tramp, true, true);
 107                __static_call_transform(tramp, __sc_insn(!func, true), func);
 108        }
 109
 110        if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
 111                __static_call_validate(site, tail, false);
 112                __static_call_transform(site, __sc_insn(!func, tail), func);
 113        }
 114
 115        mutex_unlock(&text_mutex);
 116}
 117EXPORT_SYMBOL_GPL(arch_static_call_transform);
 118