[PATCH] powerpc/rtas: Allow ibm,platform-dump RTAS call with null buffer address

[Nathan Lynch]

Andrew Donnellan <ajd at linux.ibm.com> writes:
> Add a special case to block_rtas_call() to allow the ibm,platform-dump RTAS
> call through the RTAS filter if the buffer address is 0.
>
> According to PAPR, ibm,platform-dump is called with a null buffer address
> to notify the platform firmware that processing of a particular dump is
> finished.
>
> Without this, on a pseries machine with CONFIG_PPC_RTAS_FILTER enabled, an
> application such as rtas_errd that is attempting to retrieve a dump will
> encounter an error at the end of the retrieval process.
>
> Fixes: bd59380c5ba4 ("powerpc/rtas: Restrict RTAS requests from userspace")
> Cc: stable at vger.kernel.org
> Reported-by: Sathvika Vasireddy <sathvika at linux.ibm.com>
> Signed-off-by: Andrew Donnellan <ajd at linux.ibm.com>

I agree this allows ibm,platform-dump to work without weakening the
filter for other calls. Thanks.

Reviewed-by: Nathan Lynch <nathanl at linux.ibm.com>