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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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