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    SubjectRe: [PATCH V35 15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down
    Hi,
    On 07/15/19 at 12:59pm, Matthew Garrett wrote:
    > From: Josh Boyer <jwboyer@redhat.com>
    >
    > This option allows userspace to pass the RSDP address to the kernel, which
    > makes it possible for a user to modify the workings of hardware . Reject
    > the option when the kernel is locked down.
    >
    > Signed-off-by: Josh Boyer <jwboyer@redhat.com>
    > Signed-off-by: David Howells <dhowells@redhat.com>
    > Signed-off-by: Matthew Garrett <mjg59@google.com>
    > Reviewed-by: Kees Cook <keescook@chromium.org>
    > cc: Dave Young <dyoung@redhat.com>
    > cc: linux-acpi@vger.kernel.org
    > ---
    > drivers/acpi/osl.c | 3 ++-
    > 1 file changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
    > index 9c0edf2fc0dd..06e7cffc4386 100644
    > --- a/drivers/acpi/osl.c
    > +++ b/drivers/acpi/osl.c
    > @@ -26,6 +26,7 @@
    > #include <linux/list.h>
    > #include <linux/jiffies.h>
    > #include <linux/semaphore.h>
    > +#include <linux/security.h>
    >
    > #include <asm/io.h>
    > #include <linux/uaccess.h>
    > @@ -180,7 +181,7 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
    > acpi_physical_address pa;
    >
    > #ifdef CONFIG_KEXEC
    > - if (acpi_rsdp)
    > + if (acpi_rsdp && !security_locked_down(LOCKDOWN_ACPI_TABLES))
    > return acpi_rsdp;

    I'm very sorry I noticed this late, but have to say this will not work for
    X86 with latest kernel code.

    acpi_physical_address __init acpi_os_get_root_pointer(void)
    {
    acpi_physical_address pa;

    #ifdef CONFIG_KEXEC
    if (acpi_rsdp)
    return acpi_rsdp;
    #endif
    pa = acpi_arch_get_root_pointer();
    if (pa)
    return pa;
    [snip]

    In above code, the later acpi_arch_get_root_pointer still get acpi_rsdp
    from cmdline param if provided.

    You can check the arch/x86/boot/compressed/acpi.c, and
    arch/x86/kernel/acpi/boot.c

    In X86 early code, cmdline provided acpi_rsdp pointer will be saved in boot_params.acpi_rsdp_addr;
    and the used in x86_default_get_root_pointer

    > #endif
    > pa = acpi_arch_get_root_pointer();
    > --
    > 2.22.0.510.g264f2c817a-goog
    >

    Thanks
    Dave

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