From: Matthew Garrett Date: Wed, 8 Nov 2017 15:11:34 +0000 Subject: [15/29] ACPI: Limit access to custom_method when the kernel is locked down Origin: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit?id=5ff99c830aacf02f25816a0da427216fb63ba16d custom_method effectively allows arbitrary access to system memory, making it possible for an attacker to circumvent restrictions on module loading. Disable it if the kernel is locked down. Signed-off-by: Matthew Garrett Signed-off-by: David Howells Reviewed-by: "Lee, Chun-Yi" cc: linux-acpi@vger.kernel.org --- drivers/acpi/custom_method.c | 3 +++ 1 file changed, 3 insertions(+) Index: linux/drivers/acpi/custom_method.c =================================================================== --- linux.orig/drivers/acpi/custom_method.c +++ linux/drivers/acpi/custom_method.c @@ -29,6 +29,9 @@ static ssize_t cm_write(struct file *fil struct acpi_table_header table; acpi_status status; + if (kernel_is_locked_down("ACPI custom methods")) + return -EPERM; + if (!(*ppos)) { /* parse the table header to get the table length */ if (count <= sizeof(struct acpi_table_header))