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    Subject[PATCH 12/24] ACPI: Limit access to custom_method when the kernel is locked down
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    From: Matthew Garrett <mjg59@srcf.ucam.org>

    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 <mjg59@srcf.ucam.org>
    Signed-off-by: David Howells <dhowells@redhat.com>
    Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
    cc: linux-acpi@vger.kernel.org
    ---

    drivers/acpi/custom_method.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
    index e967c1173ba3..a07fbe999eb6 100644
    --- a/drivers/acpi/custom_method.c
    +++ b/drivers/acpi/custom_method.c
    @@ -29,6 +29,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
    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))
    \
     
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