cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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static_call.c (2595B)

      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);