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commit ac2081cdc4 upstream.
Although the arm64 single-step state machine can be fast-forwarded in
cases where we wish to generate a SIGTRAP without actually executing an
instruction, this has two major limitations outside of simply skipping
an instruction due to emulation.
1. Stepping out of a ptrace signal stop into a signal handler where
SIGTRAP is blocked. Fast-forwarding the stepping state machine in
this case will result in a forced SIGTRAP, with the handler reset to
SIG_DFL.
2. The hardware implicitly fast-forwards the state machine when executing
an SVC instruction for issuing a system call. This can interact badly
with subsequent ptrace stops signalled during the execution of the
system call (e.g. SYSCALL_EXIT or seccomp traps), as they may corrupt
the stepping state by updating the PSTATE for the tracee.
Resolve both of these issues by injecting a pseudo-singlestep exception
on entry to a signal handler and also on return to userspace following a
system call.
Cc: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Tested-by: Luis Machado <luis.machado@linaro.org>
Reported-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 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.