From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B651B185B48; Sat, 30 May 2026 00:30:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780101045; cv=none; b=lH+AOo0UIBegUvq+Aq86i+67K+a16bRn/uVSWmBhV2/J9zyUgRJ51g6ziJtyLdDprdXyMYm7Z3QKEV5ElDnsj6mkdeLS2w7pgqvGYlp6cIqsO/fn/Hz4bMJBLz8vXW3Dd7fZVZyo5Ohd8sQovZ7J5JL17Kwn09QtBtx1fzXnjaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780101045; c=relaxed/simple; bh=hf5vLWK44D61F4E5sJP0UG78k4AZAIR+Uwq9t7nH/fg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=C4+1qcgbAzgg82iCNHQaB3mzO8VXpIMfaHpL9QkQeUPzoRRJ2pbff4mGb7piHqWsGA7SNRnjkflUGsjkjswQRB6okAu1Dzkg0rT+Sps/axYG/KM1QeAoxUOvGgCdA0KmL4Qr/k48DGq6lHaSgRqGgIItIzXooKWWfVlNxwZ/xFE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iQ80oYQf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iQ80oYQf" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id BECB21F00893; Sat, 30 May 2026 00:30:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780101044; bh=6eI4zy4Tq766zXKoZs9XoR7a/knH/HX/boy0n1H0AOM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=iQ80oYQfARSQHoqXSPBGldklrCgaGUyCDgCZnKAO1puTJ4kQCnhVU4vZ+o0buzGrl 16g0/4fvolxEQWMgedD9TRFYhaM94+MnyG3zQgH1eDnH3VZqA0N2slY7fSdM05so+V OUTlRfcyo6e5ZK7GwUF1zLK0Zhj3ak6Q7mqXyloQMym/Ex4mI4EvVA425PjLCDfEoH ywt044WBwx7ep8Vh8ouChRLgfyrWxDugZLn6ptqOwxKlNwZFOxD18ifUN6UecNlAxh xMhklPSV0MiaDInxxDa7bDUFnE54njc1bPolpKplyBGdpmhsGebtuS9LhUGwYmVPa9 MrCgPsA7ulGJA== Date: Sat, 30 May 2026 03:30:40 +0300 From: Jarkko Sakkinen To: Michael Bommarito Cc: Peter Huewe , Jason Gunthorpe , James Bottomley , Herbert Xu , linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] tpm: tpm2-sessions: wait for async KPP completion in tpm_buf_append_salt Message-ID: References: <20260527184655.1919993-1-michael.bommarito@gmail.com> Precedence: bulk X-Mailing-List: linux-integrity@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260527184655.1919993-1-michael.bommarito@gmail.com> On Wed, May 27, 2026 at 02:46:55PM -0400, Michael Bommarito wrote: > tpm_buf_append_salt() in drivers/char/tpm/tpm2-sessions.c calls > crypto_kpp_generate_public_key() and crypto_kpp_compute_shared_secret() > without installing a completion callback, discards both return values, > and immediately frees the kpp_request via kpp_request_free(). When the > resolved ecdh-nist-p256 KPP backend is asynchronous (atmel-ecc, HPRE, > keembay-ocs), either operation returns -EINPROGRESS and the deferred > completion worker dereferences the freed request. > > The path fires automatically from the hwrng_fillfn kernel thread via > tpm_get_random -> tpm2_get_random -> tpm2_start_auth_session -> > tpm_buf_append_salt on every entropy poll, without any userland action. > > Install crypto_req_done as the completion callback, wrap both KPP > operations in crypto_wait_req(), and propagate errors to the caller. > The wait is a no-op for synchronous backends. > > Fixes: 1085b8276bb4 ("tpm: Add the rest of the session HMAC API") > Cc: stable@vger.kernel.org > Signed-off-by: Michael Bommarito > Assisted-by: Claude:claude-opus-4-7 > --- > > Impact: on a kernel with an async ECDH KPP provider, any local user > can reclaim the freed kpp_request slab slot and control the indirect > call through req->base.complete. A reproducer is available on request. > Filing publicly per security-bugs.rst guidance. Please send the reproducer and .config although I think I grasped what I need to put but just in case (if only for comparison). > > Notes: > > Validation (QEMU x86_64, swtpm, async ecdh-nist-p256 stub backend): > > Stock kernel: the freed kpp_request is reclaimed by an unprivileged > heap spray; the deferred completion worker jumps to a controlled > address (RIP=0x41414141) via the overwritten req->base.complete > callback pointer. Reproduces on production-hardened allocator > configs (MEMCG, RANDOM_KMALLOC_CACHES, SLAB_FREELIST_HARDENED, > SLAB_FREELIST_RANDOM, INIT_ON_FREE). > > Patched kernel: crypto_wait_req() blocks until the async backend > completes; the worker observes a live request with the correct > crypto_req_done callback installed; kpp_request_free() runs only > after both operations finish. KASAN-clean across 50 entropy polls. > > drivers/char/tpm/tpm2-sessions.c | 36 ++++++++++++++++++++++++-------- > 1 file changed, 27 insertions(+), 9 deletions(-) > > diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c > index c4da6fde748f4..a23cc3a540c55 100644 > --- a/drivers/char/tpm/tpm2-sessions.c > +++ b/drivers/char/tpm/tpm2-sessions.c > @@ -489,15 +489,17 @@ static void tpm2_KDFe(u8 z[EC_PT_SZ], const char *str, u8 *pt_u, u8 *pt_v, > sha256_final(&sctx, out); > } > > -static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > - struct tpm2_auth *auth) > +static int tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > + struct tpm2_auth *auth) > { > struct crypto_kpp *kpp; > struct kpp_request *req; > + DECLARE_CRYPTO_WAIT(wait); > struct scatterlist s[2], d[1]; > struct ecdh p = {0}; > u8 encoded_key[EC_PT_SZ], *x, *y; > unsigned int buf_len; > + int rc; > > /* secret is two sized points */ > tpm_buf_append_u16(buf, (EC_PT_SZ + 2)*2); > @@ -520,13 +522,14 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > kpp = crypto_alloc_kpp("ecdh-nist-p256", CRYPTO_ALG_INTERNAL, 0); > if (IS_ERR(kpp)) { > dev_err(&chip->dev, "crypto ecdh allocation failed\n"); > - return; > + return PTR_ERR(kpp); > } > > buf_len = crypto_ecdh_key_len(&p); > if (sizeof(encoded_key) < buf_len) { > dev_err(&chip->dev, "salt buffer too small needs %d\n", > buf_len); > + rc = -EINVAL; > goto out; > } > crypto_ecdh_encode_key(encoded_key, buf_len, &p); > @@ -535,11 +538,17 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > > /* salt is now the public point of this private key */ > req = kpp_request_alloc(kpp, GFP_KERNEL); > - if (!req) > + if (!req) { > + rc = -ENOMEM; > goto out; > + } > + kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG, > + crypto_req_done, &wait); > kpp_request_set_input(req, NULL, 0); > kpp_request_set_output(req, s, EC_PT_SZ*2); > - crypto_kpp_generate_public_key(req); > + rc = crypto_wait_req(crypto_kpp_generate_public_key(req), &wait); > + if (rc) > + goto out_free_req; > /* > * we're not done: now we have to compute the shared secret > * which is our private key multiplied by the tpm_key public > @@ -551,8 +560,9 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > kpp_request_set_input(req, s, EC_PT_SZ*2); > sg_init_one(d, auth->salt, EC_PT_SZ); > kpp_request_set_output(req, d, EC_PT_SZ); > - crypto_kpp_compute_shared_secret(req); > - kpp_request_free(req); > + rc = crypto_wait_req(crypto_kpp_compute_shared_secret(req), &wait); > + if (rc) > + goto out_free_req; > > /* > * pass the shared secret through KDFe for salt. Note salt > @@ -562,8 +572,11 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip, > */ > tpm2_KDFe(auth->salt, "SECRET", x, chip->null_ec_key_x, auth->salt); > > - out: > +out_free_req: > + kpp_request_free(req); > +out: > crypto_free_kpp(kpp); > + return rc; > } > > /** > @@ -1018,7 +1031,12 @@ int tpm2_start_auth_session(struct tpm_chip *chip) > tpm_buf_append(&buf, auth->our_nonce, sizeof(auth->our_nonce)); > > /* append encrypted salt and squirrel away unencrypted in auth */ > - tpm_buf_append_salt(&buf, chip, auth); > + rc = tpm_buf_append_salt(&buf, chip, auth); > + if (rc) { > + tpm2_flush_context(chip, null_key); > + tpm_buf_destroy(&buf); > + goto out; > + } > /* session type (HMAC, audit or policy) */ > tpm_buf_append_u8(&buf, TPM2_SE_HMAC); > > -- > 2.53.0 > > BR, Jarkko