boot_guard_record.h

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#pragma once

 
#include "fl/stl/stdint.h"
#include "fl/stl/compiler_control.h"  // FL_ALWAYS_INLINE
 
namespace fl {

struct BootGuardRecord {
    fl::u32 magic;
    fl::u32 image;     
    fl::u32 boots;     
    fl::u32 crashes;   
    fl::u32 check;     
    fl::u32 reserved[3];  // pad to one 32-byte cache line
};
 
constexpr fl::u32 kBootGuardMagic = 0xFA57B008u;
 
FL_ALWAYS_INLINE fl::u32 bootGuardCheck(fl::u32 image, fl::u32 boots, fl::u32 crashes) {
    return kBootGuardMagic ^ image ^ ~boots ^ ((crashes << 16) | (crashes >> 16)) ^ 0x5A5A5A5Au;
}

FL_ALWAYS_INLINE bool bootGuardValid(const volatile BootGuardRecord& r, fl::u32 image) {
    return r.magic == kBootGuardMagic && r.image == image &&
           r.check == bootGuardCheck(image, r.boots, r.crashes);
}

FL_ALWAYS_INLINE fl::u32 bootGuardDecode(const volatile BootGuardRecord& r, fl::u32 image) {
    return bootGuardValid(r, image) ? r.boots : 0;
}

FL_ALWAYS_INLINE fl::u32 bootGuardDecodeCrashes(const volatile BootGuardRecord& r,
                                                fl::u32 image) {
    return bootGuardValid(r, image) ? r.crashes : 0;
}

FL_ALWAYS_INLINE void bootGuardStore(volatile BootGuardRecord& r, fl::u32 image,
                                     fl::u32 boots, fl::u32 crashes) {
    r.magic = kBootGuardMagic;
    r.image = image;
    r.boots = boots;
    r.crashes = crashes;
    r.check = bootGuardCheck(image, boots, crashes);
    r.reserved[0] = 0;
    r.reserved[1] = 0;
    r.reserved[2] = 0;
}

FL_ALWAYS_INLINE void bootGuardEncode(volatile BootGuardRecord& r, fl::u32 image,
                                      fl::u32 boots) {
    bootGuardStore(r, image, boots, bootGuardDecodeCrashes(r, image));
}

FL_ALWAYS_INLINE void bootGuardEncodeCrashes(volatile BootGuardRecord& r, fl::u32 image,
                                             fl::u32 crashes) {
    bootGuardStore(r, image, bootGuardDecode(r, image), crashes);
}

FL_ALWAYS_INLINE fl::u32 bootGuardHashWords(const volatile fl::u32* words, fl::u32 count,
                                            fl::u32 stride = 1) {
    fl::u32 h = 0x811C9DC5u;
    for (fl::u32 i = 0; i < count; i += stride) {
        h = (h ^ words[i]) * 0x01000193u;
    }
    return h;
}

struct BootGuardDecision {
    fl::u32 boots;   
    bool    escape;  
};

FL_ALWAYS_INLINE BootGuardDecision bootGuardOnBoot(fl::u32 stored_boots,
                                                   fl::u32 escape_boots) {
    BootGuardDecision d;
    const fl::u32 boots = stored_boots + 1;
    d.escape = escape_boots != 0 && boots >= escape_boots;
    d.boots = d.escape ? 0 : boots;
    return d;
}
 
}  // namespace fl