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Re: [PATCH 1/7] semihosting: Allow optional use of semihosting from user

From: Alex Bennée
Subject: Re: [PATCH 1/7] semihosting: Allow optional use of semihosting from userspace
Date: Tue, 16 Aug 2022 09:50:57 +0100
User-agent: mu4e 1.8.9; emacs 28.1.91

Peter Maydell <peter.maydell@linaro.org> writes:

> Currently our semihosting implementations generally prohibit use of
> semihosting calls in system emulation from the guest userspace.  This
> is a very long standing behaviour justified originally "to provide
> some semblance of security" (since code with access to the
> semihosting ABI can do things like read and write arbitrary files on
> the host system).  However, it is sometimes useful to be able to run
> trusted guest code which performs semihosting calls from guest
> userspace, notably for test code.  Add a command line suboption to
> the existing semihosting-config option group so that you can
> explicitly opt in to semihosting from guest userspace with
>  -semihosting-config userspace=on
> (There is no equivalent option for the user-mode emulator, because
> there by definition all code runs in userspace and has access to
> semihosting already.)
> This commit adds the infrastructure for the command line option and
> adds a bool 'is_user' parameter to the function
> semihosting_userspace_enabled() that target code can use to check
> whether it should be permitting the semihosting call for userspace.
> It mechanically makes all the callsites pass 'false', so they
> continue checking "is semihosting enabled in general".  Subsequent
> commits will make each target that implements semihosting honour the
> userspace=on option by passing the correct value and removing
> whatever "don't do this for userspace" checking they were doing by
> hand.
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Acked-by: Alex Bennée <alex.bennee@linaro.org>

Alex Bennée

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