1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
  4 */
  5#include <linux/bug.h>
  6#include <linux/rethook.h>
  7#include <linux/kprobes.h>
  8#include <linux/objtool.h>
  9
 10#include "kprobes/common.h"
 11
 12__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);
 13
 14#ifndef ANNOTATE_NOENDBR
 15#define ANNOTATE_NOENDBR
 16#endif
 17
 18/*
 19 * When a target function returns, this code saves registers and calls
 20 * arch_rethook_trampoline_callback(), which calls the rethook handler.
 21 */
 22asm(
 23	".text\n"
 24	".global arch_rethook_trampoline\n"
 25	".type arch_rethook_trampoline, @function\n"
 26	"arch_rethook_trampoline:\n"
 27#ifdef CONFIG_X86_64
 28	ANNOTATE_NOENDBR	/* This is only jumped from ret instruction */
 29	/* Push a fake return address to tell the unwinder it's a rethook. */
 30	"	pushq $arch_rethook_trampoline\n"
 31	UNWIND_HINT_FUNC
 32	"       pushq $" __stringify(__KERNEL_DS) "\n"
 33	/* Save the 'sp - 16', this will be fixed later. */
 34	"	pushq %rsp\n"
 35	"	pushfq\n"
 36	SAVE_REGS_STRING
 37	"	movq %rsp, %rdi\n"
 38	"	call arch_rethook_trampoline_callback\n"
 39	RESTORE_REGS_STRING
 40	/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
 41	"	addq $16, %rsp\n"
 42	"	popfq\n"
 43#else
 44	/* Push a fake return address to tell the unwinder it's a rethook. */
 45	"	pushl $arch_rethook_trampoline\n"
 46	UNWIND_HINT_FUNC
 47	"	pushl %ss\n"
 48	/* Save the 'sp - 8', this will be fixed later. */
 49	"	pushl %esp\n"
 50	"	pushfl\n"
 51	SAVE_REGS_STRING
 52	"	movl %esp, %eax\n"
 53	"	call arch_rethook_trampoline_callback\n"
 54	RESTORE_REGS_STRING
 55	/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
 56	"	addl $8, %esp\n"
 57	"	popfl\n"
 58#endif
 59	ASM_RET
 60	".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
 61);
 62NOKPROBE_SYMBOL(arch_rethook_trampoline);
 63
 64/*
 65 * Called from arch_rethook_trampoline
 66 */
 67__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
 68{
 69	unsigned long *frame_pointer;
 70
 71	/* fixup registers */
 72	regs->cs = __KERNEL_CS;
 73#ifdef CONFIG_X86_32
 74	regs->gs = 0;
 75#endif
 76	regs->ip = (unsigned long)&arch_rethook_trampoline;
 77	regs->orig_ax = ~0UL;
 78	regs->sp += 2*sizeof(long);
 79	frame_pointer = (long *)(regs + 1);
 80
 81	/*
 82	 * The return address at 'frame_pointer' is recovered by the
 83	 * arch_rethook_fixup_return() which called from this
 84	 * rethook_trampoline_handler().
 85	 */
 86	rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
 87
 88	/*
 89	 * Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
 90	 * can do RET right after POPF.
 91	 */
 92	*(unsigned long *)&regs->ss = regs->flags;
 93}
 94NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
 95
 96/*
 97 * arch_rethook_trampoline() skips updating frame pointer. The frame pointer
 98 * saved in arch_rethook_trampoline_callback() points to the real caller
 99 * function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
100 * a standard stack frame with CONFIG_FRAME_POINTER=y.
101 * Let's mark it non-standard function. Anyway, FP unwinder can correctly
102 * unwind without the hint.
103 */
104STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
105
106/* This is called from rethook_trampoline_handler(). */
107void arch_rethook_fixup_return(struct pt_regs *regs,
108			       unsigned long correct_ret_addr)
109{
110	unsigned long *frame_pointer = (void *)(regs + 1);
111
112	/* Replace fake return address with real one. */
113	*frame_pointer = correct_ret_addr;
114}
115NOKPROBE_SYMBOL(arch_rethook_fixup_return);
116
117void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
118{
119	unsigned long *stack = (unsigned long *)regs->sp;
120
121	rh->ret_addr = stack[0];
122	rh->frame = regs->sp;
123
124	/* Replace the return addr with trampoline addr */
125	stack[0] = (unsigned long) arch_rethook_trampoline;
126}
127NOKPROBE_SYMBOL(arch_rethook_prepare);