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'regno' is directly controlled by user space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability. On PTRACE_SETREGS and PTRACE_GETREGS requests, user space passes the register number that would be read or written. This register number is called 'regno' which is part of the 'addr' syscall parameter. This 'regno' value is checked against the maximum pt_regs structure size, and then used to dereference it, which matches the initial part of a Spectre v1 (and Spectre v1.1) attack. The dereferenced value, then, is returned to userspace in the GETREGS case. This patch sanitizes 'regno' before using it to dereference pt_reg. Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1]. [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2 Signed-off-by: Breno Leitao <leitao@debian.org> Acked-by: Gustavo A. R. Silva <gustavo@embeddedor.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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.