From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lamorak.hansenpartnership.com (lamorak.hansenpartnership.com [198.37.111.173]) (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 1D8A18462; Mon, 25 May 2026 17:50:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.37.111.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779731456; cv=none; b=fIIHAqhdNTQ32cqJo6yxts5Rlm4vKzAsFPyA+r+izjVFfiQNR0m4lbFF8KDT139F919banQ9xbK15lGnXRUpY9ohkWaT8Gi1SrWhWJOlBtsfFVmqPekghSIZDS36/dcPhTonraz3Bg7eY4O4siHhu3cQi7JFLO1kkJUC2dp2CNA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779731456; c=relaxed/simple; bh=FedhdqjTFv1/zylSSzRxEuWjsfGN3FMNd+XweK+qnRQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=sEWRUmt5g/0QGKoJlifDTRTQLiqcFOaViTitdtgtlbtCB/j2fHPbbjn7REEs6eA25x5C76TLsWbRxg46udzTA1IF4iG+93lBP0zPLyuzeaU4QFMc9twPSw2aIMAHmgXJc72mivlvpbUVuNPui7fiDcNFp9F92HQ4tleQW1zU4l8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com; spf=pass smtp.mailfrom=HansenPartnership.com; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b=U20FpC4f; arc=none smtp.client-ip=198.37.111.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="U20FpC4f" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1779731452; bh=FedhdqjTFv1/zylSSzRxEuWjsfGN3FMNd+XweK+qnRQ=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=U20FpC4fKR09EMjwqesTU9eyM3IqM7q+yifvHOv/rA+5cWSIYDeQJRdgvjEYebllg YV0mVnlSia6k4cQ+EVVcJOIuJ9O7Z1wob8PHegoTVYh3xR34SK0UeFP4DuQN8WesgR aXyk+K0H2MPDV/JjTqsAPUN4hjLW0CEfYunN8Y9w= Received: from lingrow.int.hansenpartnership.com (unknown [IPv6:2601:5c4:4300:d341::8c71]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lamorak.hansenpartnership.com (Postfix) with ESMTPSA id 348B51C0260; Mon, 25 May 2026 13:50:52 -0400 (EDT) Message-ID: <33b4a34ceea0934e238c08e0256b975511ef99c8.camel@HansenPartnership.com> Subject: Re: [PATCH] tpm-buf: memory-safe allocations From: James Bottomley To: Jarkko Sakkinen , linux-integrity@vger.kernel.org Cc: Jarkko Sakkinen , Arun Menon , "Daniel P. Smith" , Alec Brown , Ross Philipson , Stefan Berger , Peter Huewe , Jason Gunthorpe , Mimi Zohar , David Howells , Paul Moore , James Morris , "Serge E. Hallyn" , linux-kernel@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org Date: Mon, 25 May 2026 13:50:51 -0400 In-Reply-To: <20260522013555.1063716-1-jarkko@kernel.org> References: <20260522013555.1063716-1-jarkko@kernel.org> Autocrypt: addr=James.Bottomley@HansenPartnership.com; 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AHBLpBdnl9SOe8ETkv6GqbZrXUED/dAbRVIT5vHP51zyYB8rAUjp3PnzxsXFG8eQaacEyKSl0DKDlgKuQ+k292LVGJhEva8z4cwg3JcrQWzbpTRskQRP624aQ7t0LKbNfXqfYT13TvZNTDdjQaCJRJ3EG8uXOszVKuc0guXunZPmmq6x1Y3bOfOezcFYoywwL3nKef+Z5sQrjG3/5NLeu+W Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-05-22 at 04:35 +0300, Jarkko Sakkinen wrote: > Decouple kzalloc from buffer creation, so that a managed allocation > can be > used: >=20 > struct tpm_buf *buf __free(kfree) buf =3D kzalloc(TPM_BUFSIZE, > GFP_KERNEL); > if (!buf) > return -ENOMEM; >=20 > tpm_buf_init(buf, TPM_BUFSIZE); >=20 > Alternatively, stack allocations are also possible: >=20 > u8 buf_data[512]; > struct tpm_buf *buf =3D (struct tpm_buf *)buf_data; > tpm_buf_init(buf, sizeof(buf_data)); This isn't really a good idea from a security point of view. =C2=A0Remember the buffer has to be big enough for both the sent and the received data. Today we simply set TPM_BUFSIZE to the maximum amount a TPM requires and all the send and receives just work. If we let callers set this size, we're asking for them to get it wrong (or at least forget about the receive part) and for us to get a DMA overrun from the TPM ... which might be potentially exploitable depending on how it occurs (think of an unseal of user chosen data overrunning). I get the desire to support some of the newer chunked commands, but since none of them is yet present in the kernel, why not introduce an API that works only for them to avoid the risk of a security cockup in existing code? Regards, James