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References: <20210603055341.24473-1-liuhangbin@gmail.com>
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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Thu, 3 Jun 2021 12:24:10 +0200
Message-ID: <CAHmME9qXTYVLenPBfq2xpfq=DSJAsdUwSqP4Fzc=0YP6kW+QsQ@mail.gmail.com>
Subject: Re: [PATCH] crypto: x86/curve25519 - fix cpu feature checking logic
 in mod_exit
To:     Hangbin Liu <liuhangbin@gmail.com>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Netdev <netdev@vger.kernel.org>, stable <stable@vger.kernel.org>
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On Thu, Jun 3, 2021 at 7:53 AM Hangbin Liu <liuhangbin@gmail.com> wrote:
>
> In curve25519_mod_init() the curve25519_alg will be registered only when
> (X86_FEATURE_BMI2 && X86_FEATURE_ADX). But in curve25519_mod_exit()
> it still checks (X86_FEATURE_BMI2 || X86_FEATURE_ADX) when do crypto
> unregister. This will trigger a BUG_ON in crypto_unregister_alg() as
> alg->cra_refcnt is 0 if the cpu only supports one of X86_FEATURE_BMI2
> and X86_FEATURE_ADX.
>
> Fixes: 07b586fe0662 ("crypto: x86/curve25519 - replace with formally verified implementation")
> Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
> ---
>  arch/x86/crypto/curve25519-x86_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/crypto/curve25519-x86_64.c b/arch/x86/crypto/curve25519-x86_64.c
> index 6706b6cb1d0f..38caf61cd5b7 100644
> --- a/arch/x86/crypto/curve25519-x86_64.c
> +++ b/arch/x86/crypto/curve25519-x86_64.c
> @@ -1500,7 +1500,7 @@ static int __init curve25519_mod_init(void)
>  static void __exit curve25519_mod_exit(void)
>  {
>         if (IS_REACHABLE(CONFIG_CRYPTO_KPP) &&
> -           (boot_cpu_has(X86_FEATURE_BMI2) || boot_cpu_has(X86_FEATURE_ADX)))
> +           static_branch_likely(&curve25519_use_bmi2_adx))
>                 crypto_unregister_kpp(&curve25519_alg);
>  }

Looks like the error is actually that the `||` should be a `&&`. But
if you'd like to branch on that static key instead, that's fine.

Cc: stable@vger.kernel.org
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>