On Mon, Jun 15, 2020 at 12:34:56PM +0200, Philippe Mathieu-Daudé wrote:
> On the host OS, various aspects of TLS operation are configurable.
> In particular it is possible for the sysadmin to control the TLS
> cipher/protocol algorithms that applications are permitted to use.
>
> * Any given crypto library has a built-in default priority list
> defined by the distro maintainer of the library package (or by
> upstream).
>
> * The "crypto-policies" RPM (or equivalent host OS package)
> provides a config file such as "/etc/crypto-policies/config",
> where the sysadmin can set a high level (library-independent)
> policy.
>
> The "update-crypto-policies --set" command (or equivalent) is
> used to translate the global policy to individual library
> representations, producing files such as
> "/etc/crypto-policies/back-ends/*.config". The generated files,
> if present, are loaded by the various crypto libraries to
> override their own built-in defaults.
>
> For example, the GNUTLS library may read
> "/etc/crypto-policies/back-ends/gnutls.config".
>
> * A management application (or the QEMU user) may overide the
> system-wide crypto-policies config via their own config, if
> they need to diverge from the former.
>
> Thus the priority order is "QEMU user config" > "crypto-policies
> system config" > "library built-in config".
>
> Introduce the "tls-cipher-suites" object for exposing the ordered
> list of permitted TLS cipher suites from the host side to the
> guest firmware, via fw_cfg. The list is represented as an array
> of IANA_TLS_CIPHER objects. The firmware uses the IANA_TLS_CIPHER
> array for configuring guest-side TLS, for example in UEFI HTTPS
> Boot.
>
> The priority at which the host-side policy is retrieved is given
> by the "priority" property of the new object type. For example,
> "priority=@SYSTEM" may be used to refer to
> "/etc/crypto-policies/back-ends/gnutls.config" (given that QEMU
> uses GNUTLS).
>
> [Description from Daniel P. Berrangé, edited by Laszlo Ersek.]
>
> Example of use to dump the cipher suites:
>
> $ qemu-system-x86_64 -S \
> -object tls-cipher-suites,id=mysuite,priority=@SYSTEM \
> -trace qcrypto\*
>
> Reviewed-by: Laszlo Ersek <ler...@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com>
> ---
> v9: Replaced 'backends' -> 'frontends' (lersek)
> ---
> include/crypto/tls-cipher-suites.h | 38 +++++++++
> crypto/tls-cipher-suites.c | 127 +++++++++++++++++++++++++++++
> crypto/Makefile.objs | 1 +
> crypto/trace-events | 5 ++
> qemu-options.hx | 19 +++++
> 5 files changed, 190 insertions(+)
> create mode 100644 include/crypto/tls-cipher-suites.h
> create mode 100644 crypto/tls-cipher-suites.c
>
> diff --git a/include/crypto/tls-cipher-suites.h
> b/include/crypto/tls-cipher-suites.h
> new file mode 100644
> index 0000000000..3848393a20
> --- /dev/null
> +++ b/include/crypto/tls-cipher-suites.h
> @@ -0,0 +1,38 @@
> +/*
> + * QEMU TLS Cipher Suites Registry (RFC8447)
> + *
> + * Copyright (c) 2019 Red Hat, Inc.
> + *
> + * Author: Philippe Mathieu-Daudé <phi...@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#ifndef QCRYPTO_TLSCIPHERSUITES_H
> +#define QCRYPTO_TLSCIPHERSUITES_H
> +
> +#include "qom/object.h"
> +#include "crypto/tlscreds.h"
> +
> +#define TYPE_QCRYPTO_TLS_CIPHER_SUITES "tls-cipher-suites"
> +#define QCRYPTO_TLS_CIPHER_SUITES(obj) \
> + OBJECT_CHECK(QCryptoTLSCipherSuites, (obj),
> TYPE_QCRYPTO_TLS_CIPHER_SUITES)
> +
> +/*
> + * IANA registered TLS ciphers:
> + *
> https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4
> + */
> +typedef struct {
> + uint8_t data[2];
> +} QEMU_PACKED IANA_TLS_CIPHER;
> +
> +typedef struct QCryptoTLSCipherSuites {
> + /* <private> */
> + QCryptoTLSCreds parent_obj;
> +
> + /* <public> */
> + IANA_TLS_CIPHER *cipher_list;
> + unsigned cipher_count;
There's no benefit to storing in a IANA_TLS_CIPHER struct
that I can see. If you use a GByteArray for storing the
data to match my suggestion from the previous patch, then.....
> +} QCryptoTLSCipherSuites;
> +
> +#endif /* QCRYPTO_TLSCIPHERSUITES_H */
> diff --git a/crypto/tls-cipher-suites.c b/crypto/tls-cipher-suites.c
> new file mode 100644
> index 0000000000..f02a041f9a
> --- /dev/null
> +++ b/crypto/tls-cipher-suites.c
> @@ -0,0 +1,127 @@
> +/*
> + * QEMU TLS Cipher Suites
> + *
> + * Copyright (c) 2019 Red Hat, Inc.
> + *
> + * Author: Philippe Mathieu-Daudé <phi...@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qom/object_interfaces.h"
> +#include "qemu/error-report.h"
> +#include "crypto/tlscreds.h"
> +#include "crypto/tls-cipher-suites.h"
> +#include "trace.h"
> +
> +static void parse_cipher_suites(QCryptoTLSCipherSuites *s,
> + const char *priority_name, Error **errp)
> +{
> + int ret;
> + const char *err;
> + gnutls_priority_t pcache;
> + enum { M_ENUMERATE, M_GENERATE, M_DONE } mode;
> +
> + assert(priority_name);
> + trace_qcrypto_tls_cipher_suite_priority(priority_name);
> + ret = gnutls_priority_init(&pcache, priority_name, &err);
> + if (ret < 0) {
> + error_setg(errp, "Syntax error using priority '%s': %s",
> + priority_name, gnutls_strerror(ret));
> + return;
> + }
> +
> + for (mode = M_ENUMERATE; mode < M_DONE; mode++) {
> + size_t i;
....this extra loop is not neccessary....
> +
> + for (i = 0;; i++) {
> + int ret;
> + unsigned idx;
> + const char *name;
> + IANA_TLS_CIPHER cipher;
> + gnutls_protocol_t protocol;
> +
> + ret = gnutls_priority_get_cipher_suite_index(pcache, i, &idx);
> + if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
> + break;
> + }
> + if (ret == GNUTLS_E_UNKNOWN_CIPHER_SUITE) {
> + continue;
> + }
> +
> + name = gnutls_cipher_suite_info(idx, (unsigned char *)&cipher,
> + NULL, NULL, NULL, &protocol);
> + if (name == NULL) {
> + continue;
> + }
> +
> + if (mode == M_GENERATE) {
> + const char *version;
> +
> + version = gnutls_protocol_get_name(protocol);
> + trace_qcrypto_tls_cipher_suite_info(cipher.data[0],
> + cipher.data[1],
> + version, name);
> + s->cipher_list[s->cipher_count] = cipher;
...you can just call g_byte_array_append() here. GByteArray will
efficiently grow as needed - it won't do O(N) re-allocs.
> + }
> + s->cipher_count++;
> + }
> +
> + if (mode == M_ENUMERATE) {
> + if (s->cipher_count == 0) {
> + break;
> + }
> + s->cipher_list = g_new(IANA_TLS_CIPHER, s->cipher_count);
> + s->cipher_count = 0;
> + }
> + }
> + trace_qcrypto_tls_cipher_suite_count(s->cipher_count);
> + gnutls_priority_deinit(pcache);
> +}
Regards,
Daniel
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