Source/JavaScriptCore/heap/SecurityKind.h

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#pragma once

namespace JSC {

// NOTE: SecurityKind is for distancing. But caging implies distancing. So, things that have their own
// cages (like typed arrays) don't need to worry about the security kind.
enum class SecurityKind : uint8_t {
    // The JSValueOOB security kind is for cells that contain JValues and can be accessed out-of-bounds
    // up to minimumDistanceBetweenCellsFromDifferentOrigins.
    //
    // JSValues can reference cells in JSValueOOB. Therefore, JSValues can only reference cells in
    // JSValueOOB - otherwise a Spectre OOB attack would be able to violate the rules of JSValueStrict
    // and DangerousBits.
    //
    // The OOB space is the space that depends on the heap's distancing to do OOB protection.
    JSValueOOB,
    
    // The JSValueStrict security kind is for cells that contain JSValues but cannot be accessed
    // out-of-bounds. Currently, it's not essential to keep this separate from DangerousBits. We're
    // using this to get some wiggle room for how we handle array elements. For example, we might want
    // to allow OOB reads but not OOB writes, since JSValueStrict contains only JSValues and length fields.
    // Using Spectre to read the length fields is not useful for attackers since they can read them anyway.
    // So, they will only want to write to length fields, in order to confuse a subsequent bounds check.
    // They can do that within a speculation window. However, we currently use precise index masking for
    // this.
    //
    // It's illegal to use this for any subclass of JSObject, JSString, or Symbol, or any other cell
    // that could be referenced from a JSValue. You must use poisoned pointers to point at these cells.
    JSValueStrict,
    
    // The DangerousBits security kind is for cells that contain values that could be usefully type-
    // confused with JSValue.
    //
    // It's illegal to use this for any subclass of JSObject, JSString, or Symbol, or any other cell
    // that could be referenced from a JSValue. You must use poisoned pointers to point at these cells.
    DangerousBits
};

} // namespace JSC

namespace WTF {

class PrintStream;

void printInternal(PrintStream&, JSC::SecurityKind);

} // namespace WTF