Re: [PATCH v9 4/5] crypto: Add tls-cipher-suites object

[Daniel P . Berrangé]

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 <lersek@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@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 <philmd@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 <philmd@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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