Atmosphere/stratosphere/loader/source/ldr_patcher.cpp

#include <cstdlib>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <dirent.h>

#include <switch.h>
#include "ldr_patcher.hpp"

/* IPS Patching adapted from Luma3DS (https://github.com/AuroraWright/Luma3DS/blob/master/sysmodules/loader/source/patcher.c) */

#define IPS_MAGIC "PATCH"
#define IPS_TAIL "EOF"

#define IPS32_MAGIC "IPS32"
#define IPS32_TAIL "EEOF"

static inline u8 HexNybbleToU8(const char nybble) {
    if ('0' <= nybble && nybble <= '9') {
        return nybble - '0';
    } else if ('a' <= nybble && nybble <= 'f') {
        return nybble - 'a' + 0xa;
    } else {
        return nybble - 'A' + 0xA;
    }
}

static bool MatchesBuildId(const char *name, size_t name_len, const u8 *build_id) {
    /* Validate name is hex build id. */
    for (unsigned int i = 0; i < name_len - 4; i++) {
        if (!(('0' <= name[i] && name[i] <= '9') ||
            ('a' <= name[i] && name[i] <= 'f') ||
            ('A' <= name[i] && name[i] <= 'F'))) {
                return false;
            }
    }
    
    /* Read build id from name. */
    u8 build_id_from_name[0x20] = {0};
    for (unsigned int name_ofs = 0, id_ofs = 0; name_ofs < name_len - 4; id_ofs++) {
        build_id_from_name[id_ofs] |= HexNybbleToU8(name[name_ofs++]) << 4;
        build_id_from_name[id_ofs] |= HexNybbleToU8(name[name_ofs++]);
    }
    
    return memcmp(build_id, build_id_from_name, sizeof(build_id_from_name)) == 0;
}

static void ApplyIpsPatch(u8 *mapped_nso, size_t mapped_size, bool is_ips32, FILE *f_ips) {
    u8 buffer[4];
    while (fread(buffer, is_ips32 ? 4 : 3, 1, f_ips) == 1) {
        if (is_ips32 && memcmp(buffer, IPS32_TAIL, 4) == 0) {
            break;
        } else if (!is_ips32 && memcmp(buffer, IPS_TAIL, 3) == 0) {
            break;
        }
        
        /* Offset of patch. */
        u32 patch_offset;
        if (is_ips32) {
           patch_offset = (buffer[0] << 24) | (buffer[1] << 16) | (buffer[2] << 8) | buffer[3];
        } else {
           patch_offset = (buffer[0] << 16) | (buffer[1] << 8) | (buffer[2]);
        }
        
        /* Size of patch. */
        if (fread(buffer, 2, 1, f_ips) != 1) {
            break;
        }
        u32 patch_size = (buffer[0] << 8) | (buffer[1]);
        
        /* Check for RLE encoding. */
        if (patch_size == 0) {
            /* Size of RLE. */
            if (fread(buffer, 2, 1, f_ips) != 1) {
                break;
            }
            
            u32 rle_size = (buffer[0] << 8) | (buffer[1]);
            
            /* Value for RLE. */
            if (fread(buffer, 1, 1, f_ips) != 1) {
                break;
            }
            
            if (patch_offset < sizeof(NsoUtils::NsoHeader)) {
                if (patch_offset + rle_size > sizeof(NsoUtils::NsoHeader)) {
                    u32 diff = sizeof(NsoUtils::NsoHeader) - patch_offset;
                    patch_offset += diff;
                    rle_size -= diff;
                    goto IPS_RLE_PATCH_OFFSET_WITHIN_BOUNDS;
                }
            } else {
                IPS_RLE_PATCH_OFFSET_WITHIN_BOUNDS:
                patch_offset -= sizeof(NsoUtils::NsoHeader);
                if (patch_offset + rle_size > mapped_size) {
                    rle_size = mapped_size - patch_offset;
                }
                memset(mapped_nso + patch_offset, buffer[0], rle_size);
            }
        } else {
            if (patch_offset < sizeof(NsoUtils::NsoHeader)) {
                if (patch_offset + patch_size > sizeof(NsoUtils::NsoHeader)) {
                    u32 diff = sizeof(NsoUtils::NsoHeader) - patch_offset;
                    patch_offset += diff;
                    patch_size -= diff;
                    fseek(f_ips, diff, SEEK_CUR);
                    goto IPS_DATA_PATCH_OFFSET_WITHIN_BOUNDS;
                } else {
                    fseek(f_ips, patch_size, SEEK_CUR);
                }
            } else {
                IPS_DATA_PATCH_OFFSET_WITHIN_BOUNDS:
                patch_offset -= sizeof(NsoUtils::NsoHeader);
                u32 read_size = patch_size;
                if (patch_offset + read_size > mapped_size) {
                    read_size = mapped_size - patch_offset;
                }
                if (fread(mapped_nso + patch_offset, read_size, 1, f_ips) != 1) {
                    break;
                }
                if (patch_size > read_size) {
                    fseek(f_ips, patch_size - read_size, SEEK_CUR);
                }
            }
        }
    }
}

void PatchUtils::ApplyPatches(const NsoUtils::NsoHeader *header, u8 *mapped_nso, size_t mapped_size) {
    /* Inspect all patches from /atmosphere/exefs_patches/<*>/<*>.ips */
    char path[FS_MAX_PATH+1] = {0};
    snprintf(path, sizeof(path) - 1, "sdmc:/atmosphere/exefs_patches");
    DIR *patches_dir = opendir(path);
    struct dirent *pdir_ent;
    if (patches_dir != NULL) {
        /* Iterate over the patches directory to find patch subdirectories. */
        while ((pdir_ent = readdir(patches_dir)) != NULL) {
            if (strcmp(pdir_ent->d_name, ".") == 0 || strcmp(pdir_ent->d_name, "..") == 0) {
                continue;
            }
            snprintf(path, sizeof(path) - 1, "sdmc:/atmosphere/exefs_patches/%s", pdir_ent->d_name);
            DIR *patch_dir = opendir(path);
            struct dirent *ent;
            if (patch_dir != NULL) {
                /* Iterate over the patch subdirectory to find .ips patches. */
                while ((ent = readdir(patch_dir)) != NULL) {
                    if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0) {
                        continue;
                    }
                    size_t name_len = strlen(ent->d_name);
                    if ((4 < name_len && name_len <= 0x44) && ((name_len & 1) == 0) && strcmp(ent->d_name + name_len - 4, ".ips") == 0 && MatchesBuildId(ent->d_name, name_len, header->build_id)) {
                        snprintf(path, sizeof(path) - 1, "sdmc:/atmosphere/exefs_patches/%s/%s", pdir_ent->d_name, ent->d_name);
                        FILE *f_ips = fopen(path, "rb");
                        if (f_ips != NULL) {
                            u8 header[5];
                            if (fread(header, 5, 1, f_ips) == 1) {
                                if (memcmp(header, IPS_MAGIC, 5) == 0) {
                                    ApplyIpsPatch(mapped_nso, mapped_size, false, f_ips);
                                } else if (memcmp(header, IPS32_MAGIC, 5) == 0) {
                                    ApplyIpsPatch(mapped_nso, mapped_size, true, f_ips);
                                }
                            }
                            fclose(f_ips);
                        }
                    }
                }
                closedir(patch_dir);
            }
        }
        closedir(patches_dir);
    }
}