markSecret

Function parameters

Parameters

ptr:anytype
action:enum { classify, declassify }

Compares two arrays in constant time (for a given length) and returns whether they are equal.

Functions

eql: Compares two arrays in constant time (for a given length) and returns whether they are equal.
compare: Compare two integers serialized as arrays of the same size, in constant time.
add: Add two integers serialized as arrays of the same size, in constant time.
sub: Subtract two integers serialized as arrays of the same size, in constant time.
classify: Mark a value as sensitive or secret, helping to detect potential side-channel vulnerabilities.
declassify: Mark a value as non-sensitive or public, indicating it's safe from side-channel attacks.

Source

Implementation

fn markSecret(ptr: anytype, comptime action: enum { classify, declassify }) void {
    const t = @typeInfo(@TypeOf(ptr));
    if (t != .pointer) @compileError("Pointer expected - Found: " ++ @typeName(@TypeOf(ptr)));
    const p = t.pointer;
    if (p.is_allowzero) @compileError("A nullable pointer is always assumed to leak information via side channels");
    const child = @typeInfo(p.child);

    switch (child) {
        .void, .null, .comptime_int, .comptime_float => return,
        .pointer => {
            if (child.pointer.size == .Slice) {
                @compileError("Found pointer to pointer. If the intent was to pass a slice, maybe remove the leading & in the function call");
            }
            @compileError("A pointer value is always assumed leak information via side channels");
        },
        else => {
            const mem8: *const [@sizeOf(@TypeOf(ptr.*))]u8 = @ptrCast(@constCast(ptr));
            if (action == .classify) {
                std.valgrind.memcheck.makeMemUndefined(mem8);
            } else {
                std.valgrind.memcheck.makeMemDefined(mem8);
            }
        },
    }
}