On 22/9/2022 0:01, Martin Storsjö wrote:
> +static void __cdecl __attribute__((__constructor__)) init(void)
> +{
> + HCRYPTPROV crypt = 0;
> + if (__stack_chk_guard != 0)
> + return;
> +
> + if (CryptAcquireContext(&crypt, NULL, NULL, PROV_RSA_FULL,
> CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
> + if (CryptGenRandom(crypt, sizeof(__stack_chk_guard), (BYTE*)
> &__stack_chk_guard) && __stack_chk_guard != 0) {
> + CryptReleaseContext(crypt, 0);
> + return;
> + }
> + CryptReleaseContext(crypt, 0);
> + }
I guess this is just following whatever libssp does, but I did just stumble
across some talks about RNG functions elsewhere, mainly an old comment on
Mozilla's bugzilla <https://bugzilla.mozilla.org/show_bug.cgi?id=504270#c5>
recommending `RtlGenRandom` over `CryptGenRandom` and a discussion in
rust-random <https://github.com/rust-random/getrandom/issues/65> advocating for
`BCryptGenRandom` over `RtlGenRandom` and its references. Firefox, Chrome, Rust
and Go all prefer to use `RtlGenRandom` instead of `CryptGenRandom`. The
documentation of CryptGenRandom
<https://learn.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptgenrandom>
says the API is deprecated and may be removed in the future (though I doubt
they will really remove it) which may be a good reason to avoid using
`CryptGenRandom`.
Now whether to use `RtlGenRandom` or `BCryptGenRandom` as the replacement: For
UWP, `BCryptGenRandom` is the only choice. For desktop, a comment in a
BoringSSL issue <https://bugs.chromium.org/p/boringssl/issues/detail?id=307#c9>
claims that they both use "the same internal RNG infrastructure".
It seems we'd be better off replacing this use of `CryptGenRandom` with
`RtlGenRandom` for desktop and `BCryptGenRandom` for UWP. Do you think this
make sense?
> + /* Didn't manage to initialize to a strong random value; set any
> + * nonzero pointer instead. */
> + __stack_chk_guard = (void*)0xdeadbeef;
> +}
This should probably set a 64-bit value on 64-bit architectures.
Best Regards,
Alvin
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