[PATCH 4.20 069/117] acpi/nfit: Block function zero DSMs

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@xxxxxxxxx>

commit 5e9e38d0db1d29efed1dd4cf9a70115d33521be7 upstream.

In preparation for using function number 0 as an error value, prevent it
from being considered a valid function value by acpi_nfit_ctl().

Cc: <stable@xxxxxxxxxxxxxxx>
Cc: stuart hayes <stuart.w.hayes@xxxxxxxxx>
Fixes: e02fb7264d8a ("nfit: add Microsoft NVDIMM DSM command set...")
Reported-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/acpi/nfit/core.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1844,6 +1844,13 @@ static int acpi_nfit_add_dimm(struct acp
 		return 0;
 	}
 
+	/*
+	 * Function 0 is the command interrogation function, don't
+	 * export it to potential userspace use, and enable it to be
+	 * used as an error value in acpi_nfit_ctl().
+	 */
+	dsm_mask &= ~1UL;
+
 	guid = to_nfit_uuid(nfit_mem->family);
 	for_each_set_bit(i, &dsm_mask, BITS_PER_LONG)
 		if (acpi_check_dsm(adev_dimm->handle, guid,