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Each thread executing in an enclave is associated with a Thread Control Structure (TCS). The test enclave contains two hardcoded TCS. Each TCS contains meta-data used by the hardware to save and restore thread specific information when entering/exiting the enclave. The two TCS structures within the test enclave share their SSA (State Save Area) resulting in the threads clobbering each other's data. Fix this by providing each TCS their own SSA area. Additionally, there is an 8K stack space and its address is computed from the enclave entry point which is correctly done for TCS #1 that starts on the first address inside the enclave but results in out of bounds memory when entering as TCS #2. Split 8K stack space into two separate pages with offset symbol between to ensure the current enclave entry calculation can continue to be used for both threads. While using the enclave with multiple threads requires these fixes the impact is not apparent because every test up to this point enters the enclave from the first TCS. More detail about the stack fix: ------------------------------- Before this change the test enclave (test_encl) looks as follows: .tcs (2 pages): (page 1) TCS #1 (page 2) TCS #2 .text (1 page) One page of code .data (5 pages) (page 1) encl_buffer (page 2) encl_buffer (page 3) SSA (page 4 and 5) STACK encl_stack: As shown above there is a symbol, encl_stack, that points to the end of the .data segment (pointing to the end of page 5 in .data) which is also the end of the enclave. The enclave entry code computes the stack address by adding encl_stack to the pointer to the TCS that entered the enclave. When entering at TCS #1 the stack is computed correctly but when entering at TCS #2 the stack pointer would point to one page beyond the end of the enclave and a #PF would result when TCS #2 attempts to enter the enclave. The fix involves moving the encl_stack symbol between the two stack pages. Doing so enables the stack address computation in the entry code to compute the correct stack address for each TCS. Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lkml.kernel.org/r/a49dc0d85401db788a0a3f0d795e848abf3b1f44.1636997631.git.reinette.chatre@intel.com |
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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 Restructured Text 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.