[PATCH] crypto: x86/curve25519 - fix cpu feature checking logic in mod_exit

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 <redacted>
---
 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);
 }
 

-- 
2.26.3

On Thu, Jun 3, 2021 at 7:53 AM Hangbin Liu [off-list ref] wrote:

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>

On Thu, Jun 3, 2021 at 6:24 PM Jason A. Donenfeld [off-list ref] wrote:

quoted

        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.

Yes, the code would be shorter by checking the static key :)

Thanks
hangbin

On Thu, Jun 03, 2021 at 01:53:40AM -0400, Hangbin Liu 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 <redacted>
---
 arch/x86/crypto/curve25519-x86_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu [off-list ref]
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt