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/**
@file hook_trampoline_common.h
@brief Common trampoline declaration
@details Copyright (c) 2024 Acronis International GmbH
@author Denis Kopyrin (denis.kopyrin@acronis.com)
@since $Id: $
*/
#pragma once
#include "stringify.h"
#ifdef CONFIG_RETPOLINE
#include <asm/nospec-branch.h>
#endif
// If CONFIG_RETPOLINE is on, this will be magic to mute indirect 'jmp'
#ifndef ANNOTATE_RETPOLINE_SAFE
#define ANNOTATE_RETPOLINE_SAFE ""
#endif
#ifndef ASM_ENDBR
#define ASM_ENDBR ""
#endif
// If CONFIG_RETHUNK is on, this will be magic that expands in a suitable 'ret'
#ifndef ASM_RET
#define ASM_RET "ret\n\t"
#endif
// Syscall hook may either decide to call to the original function 'fn' or return value 'ret'.
// If 'fn' is not NULL, syscall hook trampoline will jump to this function.
// If 'fn' is NULL, syscall hook trampoline will return 'ret'.
typedef struct {
long fn;
long ret;
} hook_ret_t;
// This function is called when x86_64 enters syscall.
// All parameters are in registers, push them on stack.
// As no params were changed, just call our pre-handler.
// Pop back the arguments and either call original function
// with the restored arguments or override return value.
// This asm function is the following C snippet coded to use tail jmp.
#if 0
typedef hook_ret_t (*syscall_hook_generic_t)(long a, long b, long c, long d, long e, long f);
typedef long (*syscall_generic_t)(long a, long b, long c, long d, long e, long f);
#define HOOK_TRAMPOLINE(abi, tag)
long name(long a, long b, long c, long d, long e, long f)
{
syscall_hook_generic_t fn = (syscall_hook_generic_t)(void*) fn;
hook_ret_t ret = fn(a, b, c, d, e, f);
if (ret.fn)
{
syscall_generic_t orig = (syscall_generic_t)(void*) ret.fn;
return orig(a, b, c, d, e, f);
}
else
{
return ret.ret;
}
}
#endif
// In SysV 'RDI, RSI, RDX, RCX, R8, R9' are used for passing arguments, in kernel 'RDI, RSI, RDX, R10, R8, R9'
// That's due to the fact that 'RCX' is used for syscall passing in kernel so 'RCX' is clobbered
#ifndef KERNEL_MOCK
#define HOOK_TRAMPOLINE_SIZE_DECL(name) ".size " STRINGIFY(name) ", .-" STRINGIFY(name) "\n\t"
#else
#define HOOK_TRAMPOLINE_SIZE_DECL(name)
#endif
// R10 is being pushed twice to keep the stack aligned
#define HOOK_TRAMPOLINE_ASM(name, fn) __asm__( \
".align 8;" "\n\t" \
".pushsection .text;" "\n\t" \
STRINGIFY(name) ":" "\n\t" \
ASM_ENDBR "\n\t" \
"push %rbp" "\n\t" \
"mov %rsp, %rbp" "\n\t" \
"push %rdx" "\n\t" \
"push %rdi" "\n\t" \
"push %rsi" "\n\t" \
"push %r10" "\n\t" \
"push %r10" "\n\t" \
"push %rcx" "\n\t" \
"push %r8" "\n\t" \
"push %r9" "\n\t" \
"call " STRINGIFY(fn) "\n\t" \
"test %rax, %rax" "\n\t" \
"je ._ret_" STRINGIFY(name) "\n\t" \
"pop %r9" "\n\t" \
"pop %r8" "\n\t" \
"pop %rcx" "\n\t" \
"pop %r10" "\n\t" \
"pop %r10" "\n\t" \
"pop %rsi" "\n\t" \
"pop %rdi" "\n\t" \
"pop %rdx" "\n\t" \
"pop %rbp" "\n\t" \
"" ANNOTATE_RETPOLINE_SAFE "jmpq *%rax" "\n\t" \
"._ret_" STRINGIFY(name) ":" "\n\t" \
"mov %rdx, %rax" "\n\t" \
"pop %r9" "\n\t" \
"pop %r8" "\n\t" \
"pop %rcx" "\n\t" \
"pop %r10" "\n\t" \
"pop %r10" "\n\t" \
"pop %rsi" "\n\t" \
"pop %rdi" "\n\t" \
"pop %rdx" "\n\t" \
"pop %rbp" "\n\t" \
"" ASM_RET "" "\n\t" \
".popsection;" "\n\t" \
".type " STRINGIFY(name) ", @function;" "\n\t" \
HOOK_TRAMPOLINE_SIZE_DECL(name) "\n\t" \
);