redpill-lkm5/internal/override/override_symbol.h

#ifndef REDPILLLKM_OVERRIDE_KFUNC_H
#define REDPILLLKM_OVERRIDE_KFUNC_H

#include <linux/types.h>
#include <linux/err.h> //PTR_ERR, IS_ERR

typedef struct override_symbol_inst override_symbol_inst;

/************************************************* Current interface **************************************************/
/**
 * Calls the original symbol, returning nothing, that was previously overridden
 *
 * @param sym pointer to a override_symbol_inst
 * @param ... any arguments to the original function
 *
 * @return 0 if the execution succeeded, -E if it didn't
 */
#define call_overridden_symbol_void(sym, ...) ({              \
    int __ret;                                                \
    bool __was_installed = symbol_is_overridden(sym);         \
    _Pragma("GCC diagnostic push")                            \
    _Pragma("GCC diagnostic ignored \"-Wstrict-prototypes\"") \
    void (*__ptr)() = __get_org_ptr(sym);                     \
    _Pragma("GCC diagnostic pop")                             \
    __ret = __disable_symbol_override(sym);                   \
    if (likely(__ret == 0)) {                                 \
        __ptr(__VA_ARGS__);                                   \
        if (likely(__was_installed)) {                        \
        __ret = __enable_symbol_override(sym);                \
        }                                                     \
    }                                                         \
    __ret;                                                    \
});

/**
 * Calls the original symbol, returning a value, that was previously overridden
 *
 * @param out_var name of the variable where original function return value should be placed
 * @param sym pointer to a override_symbol_inst
 * @param ... any arguments to the original function
 *
 * @return 0 if the execution succeeded, -E if it didn't
 */
#define call_overridden_symbol(out_var, sym, ...) ({          \
    int __ret;                                                \
    bool __was_installed = symbol_is_overridden(sym);         \
    _Pragma("GCC diagnostic push")                            \
    _Pragma("GCC diagnostic ignored \"-Wstrict-prototypes\"") \
    typeof (out_var) (*__ptr)() = __get_org_ptr(sym);         \
    _Pragma("GCC diagnostic pop")                             \
    __ret = __disable_symbol_override(sym);                   \
    if (likely(__ret == 0)) {                                 \
        out_var = __ptr(__VA_ARGS__);                         \
        if (likely(__was_installed)) {                        \
            __ret = __enable_symbol_override(sym);            \
        }                                                     \
    }                                                         \
    __ret;                                                    \
});

/**
 * override_symbol() with automatic error handling. See the original function for details.
 *
 * @param ptr_var Variable to store ovs pointer
 */
#define override_symbol_or_exit_int(ptr_var, name, new_sym_ptr) \
    (ptr_var) = override_symbol(name, new_sym_ptr); \
    if (unlikely(IS_ERR((ptr_var)))) { \
        int _err = PTR_ERR((ptr_var)); \
        pr_loc_err("Failed to override %s - error=%d", name, _err); \
        (ptr_var) = NULL; \
        return _err; \
    } \

/**
 * Overrides a kernel symbol with something else of your choice
 *
 * @param name Name of the kernel symbol (function) to override
 * @param new_sym_ptr An address/pointer to a new function
 *
 * @return Instance of override_symbol_inst struct pointer on success, ERR_PTR(-E) on error
 *
 * @example
 *     struct override_symbol_inst *ovi;
 *     int null_printk() {
 *         int print_res;
 *         call_overridden_symbol(print_res, ovi, "No print for you!");
 *         return print_res;
 *     }
 *     ovi = override_symbol("printk", null_printk);
 *     if (IS_ERR(ovi)) { ... handle error ... }
 *     ...
 *     restore_symbol(backup_addr, backup_code); //restore backed-up copy of printk()
 *
 * @todo: This should be rewritten using INSN without inline ASM wizardy, but this is much more complex
 */
struct override_symbol_inst* __must_check override_symbol(const char *name, const void *new_sym_ptr);

/**
 * Restores symbol overridden by override_symbol()
 *
 * For details see override_symbol() docblock
 *
 * @return 0 on success, -E on error
 */
int restore_symbol(struct override_symbol_inst *sym);

/**
 * Frees the symbol previously reserved by get_ov_symbol_instance() (e.g. via override_symbol)
 *
 * !! READ THIS SERIOUS WARNING BELOW CAREFULLY !!
 * STOP! DO NOT USE THIS if you don't understand what it does and why it exists. This function should be called from
 * outside of this submodule ONLY if the overridden code disappeared from memory. This practically can happen only when
 * you override a symbol inside of a loadable module and the module is unloaded. In ANY other case you must call
 * restore_symbol() to actually restore the original code. This function simply "forgets" about the override and frees
 * memory (as if external module has been unloaded we are NOT allowed to touch that memory anymore as it may be freed).
 * It is explicitly NOT necessary to call this function after restore_symbol() as it does so internally.
 */
void put_overridden_symbol(struct override_symbol_inst *sym);

/**
 * Check if the given symbol override is currently active
 */
bool symbol_is_overridden(struct override_symbol_inst *sym);


/****************** Private helpers (should not be used directly by any code outside of this unit!) *******************/
#include <linux/types.h>
int __enable_symbol_override(override_symbol_inst *sym);
int __disable_symbol_override(override_symbol_inst *sym);
void * __get_org_ptr(struct override_symbol_inst *sym);

#endif //REDPILLLKM_OVERRIDE_KFUNC_H