Re: [PATCH v2 0/7] Allow semihosting from user mode

[Richard Henderson <richard.henderson@linaro.org>]

On 8/22/22 15:12, Peter Maydell wrote:
> Currently our semihosting implementations usually 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.
> 
> This patchset adds 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".
> 
> It also brings all our target architectures into line about
> how they handle semihosting. Currently these fall into three
> different groups:
> 
>   * semihosting permitted only in privileged mode and only
>     if enabled on the command line:
>     - arm
>     - m68k
>   * semihosting permitted in any mode, if enabled on the command line:
>     - mips
>     - nios2
>     - xtensa
>   * semihosting permitted only in privileged mode, but fails
>     to honour the existing "enable semihosting" option, instead
>     enabling it all the time:
>     - riscv
> 
> The effect of the new option for group 1 is:
>   * user can now optionally also allow semihosting in usermode
> 
> For group 2 it is:
>   * usermode semihosting used to be permitted, but now changes
>     to default-disabled, needing explicit enablement
> 
> For group 3 it is:
>   * semihosting overall used to be default-enabled and is
>     now default-disabled, needing explicit enablement.
>     Semihosting in usermode can also be enabled.
> 
> That means this is a "things that used to work no longer do
> unless you change your commandline" change for groups 2 and 3
> (so, mips, nios2. xtensa, riscv). Consensus seems to be that
> it's OK to call this "fixing a bug" and note it in the
> changelog/releasenotes.
> 
> Changes v1->v2:
>   * make riscv check for semihosting being disabled at
>     translate time, not runtime
> 
> Only patch 7 needs review.

Thanks, queued to semihosting-next.


r~