linux-kernel - Re: [PATCH V34 15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down

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Date:   Sat, 22 Jun 2019 16:59:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matthew Garrett <matthewgarrett@...gle.com>
Cc:     jmorris@...ei.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Josh Boyer <jwboyer@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Dave Young <dyoung@...hat.com>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH V34 15/29] acpi: Ignore acpi_rsdp kernel param when the
 kernel has been locked down

On Fri, Jun 21, 2019 at 05:03:44PM -0700, Matthew Garrett wrote:
> From: Josh Boyer <jwboyer@...hat.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@...hat.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> Signed-off-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Matthew Garrett <mjg59@...gle.com>
> cc: Dave Young <dyoung@...hat.com>
> cc: linux-acpi@...r.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 f29e427d0d1d..60cda8a0f36b 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -40,6 +40,7 @@
>  #include <linux/list.h>
>  #include <linux/jiffies.h>
>  #include <linux/semaphore.h>
> +#include <linux/security.h>
>  
>  #include <asm/io.h>
>  #include <linux/uaccess.h>
> @@ -194,7 +195,7 @@ 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;
>  #endif
>  	pa = acpi_arch_get_root_pointer();
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook