nt-lite/code/kernel/ke_firmware.c

// Firmware root discovery for optional platform drivers.

#include <kernel/ke_firmware.h>
#include <ntlite/ddk/platform.h>
#include <ntlite/memory_map.h>
#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>
#include <kernel/ke_debug.h>
#include <string.h>

#define KI_RSDP_V1_SIZE 20u
#define KI_RSDP_V2_SIZE 36u
#define KI_RSDP_MAX_SIZE 4096u

static uint64_t gAcpiRsdpPhysical;
static const char* gAcpiRootDiagnostic = "absent";
static uint8_t gAcpiRsdpRevision;

// Firmware roots must remain in reserved memory after ExitBootServices.
static bool KiFirmwareReservedSpan(const MEMORY_MAP* map, uint64_t start, uint32_t length) {
    if (!map || map->Magic != MEMORY_MAP_MAGIC ||
        map->RegionCount > MEMORY_MAX_REGIONS || !length || start > UINT64_MAX - length)
        return false;
    uint64_t end = start + length;
    for (uint32_t i = 0; i < map->RegionCount; i++) {
        const MEMORY_REGION* region = &map->Regions[i];
        if (region->Type != MemoryReserved ||
            region->Base > UINT64_MAX - region->Length)
            continue;
        if (start >= region->Base && end <= region->Base + region->Length)
            return true;
    }
    return false;
}

static bool KiFirmwareChecksumValid(const uint8_t* bytes, uint32_t length) {
    uint8_t sum = 0;
    for (uint32_t i = 0; i < length; i++) sum = (uint8_t)(sum + bytes[i]);
    return sum == 0;
}

void KeFirmwareInitialize(const BOOT_INFO* bootInfo) {
    gAcpiRsdpPhysical = 0;
    gAcpiRsdpRevision = 0;
    gAcpiRootDiagnostic = "absent";
    if (!bootInfo || !bootInfo->RsdpPhysical) return;
    if (!bootInfo->PhysicalMapBase ||
        !KiFirmwareReservedSpan(&bootInfo->MemoryMap,
                                bootInfo->RsdpPhysical, KI_RSDP_V1_SIZE) ||
        bootInfo->RsdpPhysical > UINTPTR_MAX - bootInfo->PhysicalMapBase) {
        gAcpiRootDiagnostic = "invalid physical range";
        return;
    }

    const uint8_t* rsdp = (const uint8_t*)(bootInfo->PhysicalMapBase + bootInfo->RsdpPhysical);
    if (memcmp(rsdp, "RSD PTR ", 8) != 0) {
        gAcpiRootDiagnostic = "invalid signature";
        return;
    }
    if (!KiFirmwareChecksumValid(rsdp, KI_RSDP_V1_SIZE)) {
        gAcpiRootDiagnostic = "invalid legacy checksum";
        return;
    }

    if (rsdp[15] >= 2u) {
        if (!KiFirmwareReservedSpan(&bootInfo->MemoryMap,
                                    bootInfo->RsdpPhysical, KI_RSDP_V2_SIZE)) {
            gAcpiRootDiagnostic = "truncated extended root";
            return;
        }
        uint32_t length;
        memcpy(&length, rsdp + 20, sizeof(length));
        if (length < KI_RSDP_V2_SIZE || length > KI_RSDP_MAX_SIZE ||
            !KiFirmwareReservedSpan(&bootInfo->MemoryMap,
                                    bootInfo->RsdpPhysical, length)) {
            gAcpiRootDiagnostic = "invalid extended length";
            return;
        }
        if (!KiFirmwareChecksumValid(rsdp, length)) {
            gAcpiRootDiagnostic = "invalid extended checksum";
            return;
        }
    }

    gAcpiRsdpPhysical = (uint64_t)bootInfo->RsdpPhysical;
    gAcpiRsdpRevision = rsdp[15];
    gAcpiRootDiagnostic = "valid";
}

// A driver chooses its own ACPI interpreter and maps tables through the DDK.
__declspec(dllexport) KSTATUS KeFirmwareQueryAcpiRsdp(uint64_t* physicalAddressOut) {
    if (!physicalAddressOut) return NTLSTATUS_INVALID_PARAMETER;
    *physicalAddressOut = 0;
    if (!gAcpiRsdpPhysical) return NTLSTATUS_NOT_SUPPORTED;
    *physicalAddressOut = gAcpiRsdpPhysical;
    return NTLSTATUS_SUCCESS;
}

// Reports the firmware handoff state through the normal kernel diagnostic stream.
void KeFirmwareLog(void) {
    DbgPrint("firmware: ACPI RSDP %s phys=0x%016llX revision=%u\n",
             gAcpiRootDiagnostic,
             (unsigned long long)gAcpiRsdpPhysical,
             (unsigned)gAcpiRsdpRevision);
}