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// SPDX-License-Identifier: GPL-2.0
#include <linux/static_call.h>
#include <linux/memory.h>
#include <linux/bug.h>
#include <asm/text-patching.h>
enum insn_type {
CALL = 0, /* site call */
NOP = 1, /* site cond-call */
JMP = 2, /* tramp / site tail-call */
RET = 3, /* tramp / site cond-tail-call */
JCC = 4,
};
/*
* ud1 %esp, %ecx - a 3 byte #UD that is unique to trampolines, chosen such
* that there is no false-positive trampoline identification while also being a
* speculation stop.
*/
static const u8 tramp_ud[] = { 0x0f, 0xb9, 0xcc };
/*
* cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax
*/
static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 };
static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */
{
u8 ret = 0;
if (insn[0] == 0x0f) {
u8 tmp = insn[1];
if ((tmp & 0xf0) == 0x80)
ret = tmp;
}
return ret;
}
extern void __static_call_return(void);
asm (".global __static_call_return\n\t"
".type __static_call_return, @function\n\t"
ASM_FUNC_ALIGN "\n\t"
"__static_call_return:\n\t"
ANNOTATE_NOENDBR
ANNOTATE_RETPOLINE_SAFE
"ret; int3\n\t"
".size __static_call_return, . - __static_call_return \n\t");
static void __ref __static_call_transform(void *insn, enum insn_type type,
void *func, bool modinit)
{
const void *emulate = NULL;
int size = CALL_INSN_SIZE;
const void *code;
u8 op, buf[6];
if ((type == JMP || type == RET) && (op = __is_Jcc(insn)))
type = JCC;
switch (type) {
case CALL:
func = callthunks_translate_call_dest(func);
code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
if (func == &__static_call_return0) {
emulate = code;
code = &xor5rax;
}
break;
case NOP:
code = x86_nops[5];
break;
case JMP:
code = text_gen_insn(JMP32_INSN_OPCODE, insn, func);
break;
case RET:
if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk);
else
code = &retinsn;
break;
case JCC:
if (!func) {
func = __static_call_return;
if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
func = x86_return_thunk;
}
buf[0] = 0x0f;
__text_gen_insn(buf+1, op, insn+1, func, 5);
code = buf;
size = 6;
break;
}
if (memcmp(insn, code, size) == 0)
return;
if (system_state == SYSTEM_BOOTING || modinit)
return text_poke_early(insn, code, size);
text_poke_bp(insn, code, size, emulate);
}
static void __static_call_validate(u8 *insn, bool tail, bool tramp)
{
u8 opcode = insn[0];
if (tramp && memcmp(insn+5, tramp_ud, 3)) {
pr_err("trampoline signature fail");
BUG();
}
if (tail) {
if (opcode == JMP32_INSN_OPCODE ||
opcode == RET_INSN_OPCODE ||
__is_Jcc(insn))
return;
} else {
if (opcode == CALL_INSN_OPCODE ||
!memcmp(insn, x86_nops[5], 5) ||
!memcmp(insn, xor5rax, 5))
return;
}
/*
* If we ever trigger this, our text is corrupt, we'll probably not live long.
*/
pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
BUG();
}
static inline enum insn_type __sc_insn(bool null, bool tail)
{
/*
* Encode the following table without branches:
*
* tail null insn
* -----+-------+------
* 0 | 0 | CALL
* 0 | 1 | NOP
* 1 | 0 | JMP
* 1 | 1 | RET
*/
return 2*tail + null;
}
void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
{
mutex_lock(&text_mutex);
if (tramp) {
__static_call_validate(tramp, true, true);
__static_call_transform(tramp, __sc_insn(!func, true), func, false);
}
if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
__static_call_validate(site, tail, false);
__static_call_transform(site, __sc_insn(!func, tail), func, false);
}
mutex_unlock(&text_mutex);
}
EXPORT_SYMBOL_GPL(arch_static_call_transform);
#ifdef CONFIG_MITIGATION_RETHUNK
/*
* This is called by apply_returns() to fix up static call trampolines,
* specifically ARCH_DEFINE_STATIC_CALL_NULL_TRAMP which is recorded as
* having a return trampoline.
*
* The problem is that static_call() is available before determining
* X86_FEATURE_RETHUNK and, by implication, running alternatives.
*
* This means that __static_call_transform() above can have overwritten the
* return trampoline and we now need to fix things up to be consistent.
*/
bool __static_call_fixup(void *tramp, u8 op, void *dest)
{
unsigned long addr = (unsigned long)tramp;
/*
* Not all .return_sites are a static_call trampoline (most are not).
* Check if the 3 bytes after the return are still kernel text, if not,
* then this definitely is not a trampoline and we need not worry
* further.
*
* This avoids the memcmp() below tripping over pagefaults etc..
*/
if (((addr >> PAGE_SHIFT) != ((addr + 7) >> PAGE_SHIFT)) &&
!kernel_text_address(addr + 7))
return false;
if (memcmp(tramp+5, tramp_ud, 3)) {
/* Not a trampoline site, not our problem. */
return false;
}
mutex_lock(&text_mutex);
if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk)
__static_call_transform(tramp, RET, NULL, true);
mutex_unlock(&text_mutex);
return true;
}
#endif
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