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

[Tyrel Datwyler]

On 6/14/22 06:49, Andrew Donnellan wrote:
> 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>

Similar to what is done for ibm,configure-connector with idx_buf2 and a NULL
address.

Reviewed-by: Tyrel Datwyler <tyreld at linux.ibm.com>

> ---
>  arch/powerpc/kernel/rtas.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index a6fce3106e02..693133972294 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -1071,7 +1071,7 @@ static struct rtas_filter rtas_filters[] __ro_after_init = {
>  	{ "get-time-of-day", -1, -1, -1, -1, -1 },
>  	{ "ibm,get-vpd", -1, 0, -1, 1, 2 },
>  	{ "ibm,lpar-perftools", -1, 2, 3, -1, -1 },
> -	{ "ibm,platform-dump", -1, 4, 5, -1, -1 },
> +	{ "ibm,platform-dump", -1, 4, 5, -1, -1 },		/* Special cased */
>  	{ "ibm,read-slot-reset-state", -1, -1, -1, -1, -1 },
>  	{ "ibm,scan-log-dump", -1, 0, 1, -1, -1 },
>  	{ "ibm,set-dynamic-indicator", -1, 2, -1, -1, -1 },
> @@ -1120,6 +1120,15 @@ static bool block_rtas_call(int token, int nargs,
>  				size = 1;
> 
>  			end = base + size - 1;
> +
> +			/*
> +			 * Special case for ibm,platform-dump - NULL buffer
> +			 * address is used to indicate end of dump processing
> +			 */
> +			if (!strcmp(f->name, "ibm,platform-dump") &&
> +			    base == 0)
> +				return false;
> +
>  			if (!in_rmo_buf(base, end))
>  				goto err;
>  		}