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From Daniel's cover letter: IBM Power9 processors can speculatively operate on data in the L1 cache before it has been completely validated, via a way-prediction mechanism. It is not possible for an attacker to determine the contents of impermissible memory using this method, since these systems implement a combination of hardware and software security measures to prevent scenarios where protected data could be leaked. However these measures don't address the scenario where an attacker induces the operating system to speculatively execute instructions using data that the attacker controls. This can be used for example to speculatively bypass "kernel user access prevention" techniques, as discovered by Anthony Steinhauser of Google's Safeside Project. This is not an attack by itself, but there is a possibility it could be used in conjunction with side-channels or other weaknesses in the privileged code to construct an attack. This issue can be mitigated by flushing the L1 cache between privilege boundaries of concern. This patch series flushes the L1 cache on kernel entry (patch 2) and after the kernel performs any user accesses (patch 3). It also adds a self-test and performs some related cleanups. -----BEGIN PGP SIGNATURE----- iQJHBAABCAAxFiEEJFGtCPCthwEv2Y/bUevqPMjhpYAFAl+2aqETHG1wZUBlbGxl cm1hbi5pZC5hdQAKCRBR6+o8yOGlgG+hD/4njSFct2amqWfqDYR9b2OykWmnMQXn geookk5SbItQF7vh1q2SVA6r43s5ZAxgD5fezx4LgG6p3QU39+Tr0RhzUUHWMPDV UNGZK6x/N/GSYeq0bqvMHmVwS0FDjPE8nOtA8Hn2T9mUUsu9G0okpgYPLnEu6rb1 gIyS35zlLBh9obi3MfJzyln/AmCE7hdonKRtLAxvGiERJAyfAG757lrdjrwavyHy mwz+XPl5PF88jfO5cbcZT9gNHmZZPzVsOVwNcstCh2FcwuePv9dWe1pxsBxxKqP5 UXceXPcKM7VlRNmehimq7q/hfbget4RJGGKYPNXeKHOo6yfy7lJPiQV4h+5z2pSs SPP2fQQPq0aubmcO23CXFtZl4WRHQ4pax6opepnpIfC2vZ0HLXJtPrhMKcbFJNTo qPis6HWQPpIuI6l4MJfs+YO9ETxCR31Yd28qFAfPFoHlnQZTfx6NPhw8HKxTbSh2 Svr4X6Y14j3UsQgLTCArCXWAG/hlfRwxDZJ4AvR9EU0HJGDyZ45Y+LTD1N8bbsny zcYfPqWGPIanLcNPNFYIQwDZo7ff08KdmngUvf/Q9om60mP1hsPJMHf6VhPXj4fC 2TZ11fORssSlBSNtIkFkbjEG+aiWtWnz3fN3uSyT50rgGwtDHJzVzLiUWHlZKcxW X73YdxuT8fqQwg== =Yibq -----END PGP SIGNATURE----- Merge tag 'powerpc-cve-2020-4788' into fixes From Daniel's cover letter: IBM Power9 processors can speculatively operate on data in the L1 cache before it has been completely validated, via a way-prediction mechanism. It is not possible for an attacker to determine the contents of impermissible memory using this method, since these systems implement a combination of hardware and software security measures to prevent scenarios where protected data could be leaked. However these measures don't address the scenario where an attacker induces the operating system to speculatively execute instructions using data that the attacker controls. This can be used for example to speculatively bypass "kernel user access prevention" techniques, as discovered by Anthony Steinhauser of Google's Safeside Project. This is not an attack by itself, but there is a possibility it could be used in conjunction with side-channels or other weaknesses in the privileged code to construct an attack. This issue can be mitigated by flushing the L1 cache between privilege boundaries of concern. This patch series flushes the L1 cache on kernel entry (patch 2) and after the kernel performs any user accesses (patch 3). It also adds a self-test and performs some related cleanups. |
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| Documentation | ||
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| fs | ||
| include | ||
| init | ||
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| net | ||
| samples | ||
| scripts | ||
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| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
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| README | ||
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.