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In tpm_buf_check_hmac_response(), compare the HMAC values in constant time using crypto_memneq() instead of in variable time using memcmp(). This is worthwhile to follow best practices and to be consistent with MAC comparisons elsewhere in the kernel. However, in this driver the side channel seems to have been benign: the HMAC input data is guaranteed to always be unique, which makes the usual MAC forgery via timing side channel not possible. Specifically, the HMAC input data in tpm_buf_check_hmac_response() includes the "our_nonce" field, which was generated by the kernel earlier, remains under the control of the kernel, and is unique for each call to tpm_buf_check_hmac_response(). Signed-off-by: Eric Biggers <ebiggers@kernel.org> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.