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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
*/
#include <linux/bug.h>
#include <linux/rethook.h>
#include <linux/kprobes.h>
#include <linux/objtool.h>
#include "kprobes/common.h"
__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);
#ifndef ANNOTATE_NOENDBR
#define ANNOTATE_NOENDBR
#endif
/*
* When a target function returns, this code saves registers and calls
* arch_rethook_trampoline_callback(), which calls the rethook handler.
*/
asm(
".text\n"
".global arch_rethook_trampoline\n"
".type arch_rethook_trampoline, @function\n"
"arch_rethook_trampoline:\n"
#ifdef CONFIG_X86_64
ANNOTATE_NOENDBR /* This is only jumped from ret instruction */
/* Push a fake return address to tell the unwinder it's a rethook. */
" pushq $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
" pushq $" __stringify(__KERNEL_DS) "\n"
/* Save the 'sp - 16', this will be fixed later. */
" pushq %rsp\n"
" pushfq\n"
SAVE_REGS_STRING
" movq %rsp, %rdi\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
" addq $16, %rsp\n"
" popfq\n"
#else
/* Push a fake return address to tell the unwinder it's a rethook. */
" pushl $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
" pushl %ss\n"
/* Save the 'sp - 8', this will be fixed later. */
" pushl %esp\n"
" pushfl\n"
SAVE_REGS_STRING
" movl %esp, %eax\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
" addl $8, %esp\n"
" popfl\n"
#endif
ASM_RET
".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
);
NOKPROBE_SYMBOL(arch_rethook_trampoline);
/*
* Called from arch_rethook_trampoline
*/
__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
{
unsigned long *frame_pointer;
/* fixup registers */
regs->cs = __KERNEL_CS;
#ifdef CONFIG_X86_32
regs->gs = 0;
#endif
regs->ip = (unsigned long)&arch_rethook_trampoline;
regs->orig_ax = ~0UL;
regs->sp += 2*sizeof(long);
frame_pointer = (long *)(regs + 1);
/*
* The return address at 'frame_pointer' is recovered by the
* arch_rethook_fixup_return() which called from this
* rethook_trampoline_handler().
*/
rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
/*
* Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
* can do RET right after POPF.
*/
*(unsigned long *)®s->ss = regs->flags;
}
NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
/*
* arch_rethook_trampoline() skips updating frame pointer. The frame pointer
* saved in arch_rethook_trampoline_callback() points to the real caller
* function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
* a standard stack frame with CONFIG_FRAME_POINTER=y.
* Let's mark it non-standard function. Anyway, FP unwinder can correctly
* unwind without the hint.
*/
STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
/* This is called from rethook_trampoline_handler(). */
void arch_rethook_fixup_return(struct pt_regs *regs,
unsigned long correct_ret_addr)
{
unsigned long *frame_pointer = (void *)(regs + 1);
/* Replace fake return address with real one. */
*frame_pointer = correct_ret_addr;
}
NOKPROBE_SYMBOL(arch_rethook_fixup_return);
void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
{
unsigned long *stack = (unsigned long *)regs->sp;
rh->ret_addr = stack[0];
rh->frame = regs->sp;
/* Replace the return addr with trampoline addr */
stack[0] = (unsigned long) arch_rethook_trampoline;
}
NOKPROBE_SYMBOL(arch_rethook_prepare);
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