[V38,15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down
diff mbox series

Message ID 20190808000721.124691-16-matthewgarrett@google.com
State New
Headers show
Series
  • security: Add support for locking down the kernel
Related show

Commit Message

Matthew Garrett Aug. 8, 2019, 12:07 a.m. UTC
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. This requires some reworking
of the existing RSDP command line logic, since the early boot code also
makes use of a command-line passed RSDP when locating the SRAT table
before the lockdown code has been initialised. This is achieved by
separating the command line RSDP path in the early boot code from the
generic RSDP path, and then copying the command line RSDP into boot
params in the kernel proper if lockdown is not enabled. If lockdown is
enabled and an RSDP is provided on the command line, this will only be
used when parsing SRAT (which shouldn't permit kernel code execution)
and will be ignored in the rest of the kernel.

(Modified by Matthew Garrett in order to handle the early boot RSDP
environment)

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
---
 arch/x86/boot/compressed/acpi.c | 19 +++++++++++++------
 arch/x86/include/asm/acpi.h     |  9 +++++++++
 arch/x86/include/asm/x86_init.h |  2 ++
 arch/x86/kernel/acpi/boot.c     |  5 +++++
 arch/x86/kernel/x86_init.c      |  1 +
 drivers/acpi/osl.c              | 14 +++++++++++++-
 include/linux/acpi.h            |  6 ++++++
 7 files changed, 49 insertions(+), 7 deletions(-)

Comments

Dave Young Aug. 14, 2019, 2:51 a.m. UTC | #1
On 08/07/19 at 05:07pm, 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. This requires some reworking
> of the existing RSDP command line logic, since the early boot code also
> makes use of a command-line passed RSDP when locating the SRAT table
> before the lockdown code has been initialised. This is achieved by
> separating the command line RSDP path in the early boot code from the
> generic RSDP path, and then copying the command line RSDP into boot
> params in the kernel proper if lockdown is not enabled. If lockdown is
> enabled and an RSDP is provided on the command line, this will only be
> used when parsing SRAT (which shouldn't permit kernel code execution)
> and will be ignored in the rest of the kernel.
> 
> (Modified by Matthew Garrett in order to handle the early boot RSDP
> environment)
> 
> 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
> ---
>  arch/x86/boot/compressed/acpi.c | 19 +++++++++++++------
>  arch/x86/include/asm/acpi.h     |  9 +++++++++
>  arch/x86/include/asm/x86_init.h |  2 ++
>  arch/x86/kernel/acpi/boot.c     |  5 +++++
>  arch/x86/kernel/x86_init.c      |  1 +
>  drivers/acpi/osl.c              | 14 +++++++++++++-
>  include/linux/acpi.h            |  6 ++++++
>  7 files changed, 49 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
> index 15255f388a85..149795c369f2 100644
> --- a/arch/x86/boot/compressed/acpi.c
> +++ b/arch/x86/boot/compressed/acpi.c
> @@ -26,7 +26,7 @@ struct mem_vector immovable_mem[MAX_NUMNODES*2];
>   */
>  #define MAX_ADDR_LEN 19
>  
> -static acpi_physical_address get_acpi_rsdp(void)
> +static acpi_physical_address get_cmdline_acpi_rsdp(void)
>  {
>  	acpi_physical_address addr = 0;
>  
> @@ -278,10 +278,7 @@ acpi_physical_address get_rsdp_addr(void)
>  {
>  	acpi_physical_address pa;
>  
> -	pa = get_acpi_rsdp();
> -
> -	if (!pa)
> -		pa = boot_params->acpi_rsdp_addr;
> +	pa = boot_params->acpi_rsdp_addr;
>  
>  	/*
>  	 * Try to get EFI data from setup_data. This can happen when we're a
> @@ -311,7 +308,17 @@ static unsigned long get_acpi_srat_table(void)
>  	char arg[10];
>  	u8 *entry;
>  
> -	rsdp = (struct acpi_table_rsdp *)(long)boot_params->acpi_rsdp_addr;
> +	/*
> +	 * Check whether we were given an RSDP on the command line. We don't
> +	 * stash this in boot params because the kernel itself may have
> +	 * different ideas about whether to trust a command-line parameter.
> +	 */
> +	rsdp = (struct acpi_table_rsdp *)get_cmdline_acpi_rsdp();
> +
> +	if (!rsdp)
> +		rsdp = (struct acpi_table_rsdp *)(long)
> +			boot_params->acpi_rsdp_addr;
> +
>  	if (!rsdp)
>  		return 0;
>  
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index aac686e1e005..bc9693c9107e 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -117,6 +117,12 @@ static inline bool acpi_has_cpu_in_madt(void)
>  	return !!acpi_lapic;
>  }
>  
> +#define ACPI_HAVE_ARCH_SET_ROOT_POINTER
> +static inline void acpi_arch_set_root_pointer(u64 addr)
> +{
> +	x86_init.acpi.set_root_pointer(addr);
> +}
> +
>  #define ACPI_HAVE_ARCH_GET_ROOT_POINTER
>  static inline u64 acpi_arch_get_root_pointer(void)
>  {
> @@ -125,6 +131,7 @@ static inline u64 acpi_arch_get_root_pointer(void)
>  
>  void acpi_generic_reduced_hw_init(void);
>  
> +void x86_default_set_root_pointer(u64 addr);
>  u64 x86_default_get_root_pointer(void);
>  
>  #else /* !CONFIG_ACPI */
> @@ -138,6 +145,8 @@ static inline void disable_acpi(void) { }
>  
>  static inline void acpi_generic_reduced_hw_init(void) { }
>  
> +static inline void x86_default_set_root_pointer(u64 addr) { }
> +
>  static inline u64 x86_default_get_root_pointer(void)
>  {
>  	return 0;
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index ac0934189017..19435858df5f 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -134,10 +134,12 @@ struct x86_hyper_init {
>  
>  /**
>   * struct x86_init_acpi - x86 ACPI init functions
> + * @set_root_poitner:		set RSDP address
>   * @get_root_pointer:		get RSDP address
>   * @reduced_hw_early_init:	hardware reduced platform early init
>   */
>  struct x86_init_acpi {
> +	void (*set_root_pointer)(u64 addr);
>  	u64 (*get_root_pointer)(void);
>  	void (*reduced_hw_early_init)(void);
>  };
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 17b33ef604f3..04205ce127a1 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -1760,6 +1760,11 @@ void __init arch_reserve_mem_area(acpi_physical_address addr, size_t size)
>  	e820__update_table_print();
>  }
>  
> +void x86_default_set_root_pointer(u64 addr)
> +{
> +	boot_params.acpi_rsdp_addr = addr;
> +}
> +
>  u64 x86_default_get_root_pointer(void)
>  {
>  	return boot_params.acpi_rsdp_addr;
> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> index 1bef687faf22..18a799c8fa28 100644
> --- a/arch/x86/kernel/x86_init.c
> +++ b/arch/x86/kernel/x86_init.c
> @@ -95,6 +95,7 @@ struct x86_init_ops x86_init __initdata = {
>  	},
>  
>  	.acpi = {
> +		.set_root_pointer	= x86_default_set_root_pointer,
>  		.get_root_pointer	= x86_default_get_root_pointer,
>  		.reduced_hw_early_init	= acpi_generic_reduced_hw_init,
>  	},
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 9c0edf2fc0dd..d43df3a3fa8d 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>
> @@ -180,8 +181,19 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
>  	acpi_physical_address pa;
>  
>  #ifdef CONFIG_KEXEC
> -	if (acpi_rsdp)
> +	/*
> +	 * We may have been provided with an RSDP on the command line,
> +	 * but if a malicious user has done so they may be pointing us
> +	 * at modified ACPI tables that could alter kernel behaviour -
> +	 * so, we check the lockdown status before making use of
> +	 * it. If we trust it then also stash it in an architecture
> +	 * specific location (if appropriate) so it can be carried
> +	 * over further kexec()s.
> +	 */
> +	if (acpi_rsdp && !security_locked_down(LOCKDOWN_ACPI_TABLES)) {
> +		acpi_arch_set_root_pointer(acpi_rsdp);
>  		return acpi_rsdp;
> +	}
>  #endif
>  	pa = acpi_arch_get_root_pointer();
>  	if (pa)
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index e40e1e27ed8e..6b35f2f4cab3 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -643,6 +643,12 @@ bool acpi_gtdt_c3stop(int type);
>  int acpi_arch_timer_mem_init(struct arch_timer_mem *timer_mem, int *timer_count);
>  #endif
>  
> +#ifndef ACPI_HAVE_ARCH_SET_ROOT_POINTER
> +static inline void acpi_arch_set_root_pointer(u64 addr)
> +{
> +}
> +#endif
> +
>  #ifndef ACPI_HAVE_ARCH_GET_ROOT_POINTER
>  static inline u64 acpi_arch_get_root_pointer(void)
>  {
> -- 
> 2.22.0.770.g0f2c4a37fd-goog
> 

I'm not sure why this series get posted quickly again.  As for this
patch it was restructured according the early rsdp parsing code, so
personally I think keep the original Reviewed-by is questionable and it
needs another review.  But I did not find time to read it carefully.

Add several cc to void it slipped.

Thanks
Dave
Borislav Petkov Aug. 14, 2019, 7:26 a.m. UTC | #2
On Wed, Aug 07, 2019 at 05:07:07PM -0700, 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. This requires some reworking
> of the existing RSDP command line logic, since the early boot code also
> makes use of a command-line passed RSDP when locating the SRAT table
> before the lockdown code has been initialised. This is achieved by
> separating the command line RSDP path in the early boot code from the
> generic RSDP path, and then copying the command line RSDP into boot
> params in the kernel proper if lockdown is not enabled. If lockdown is
> enabled and an RSDP is provided on the command line, this will only be
> used when parsing SRAT (which shouldn't permit kernel code execution)
> and will be ignored in the rest of the kernel.
> 
> (Modified by Matthew Garrett in order to handle the early boot RSDP
> environment)
> 
> 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
> ---
>  arch/x86/boot/compressed/acpi.c | 19 +++++++++++++------
>  arch/x86/include/asm/acpi.h     |  9 +++++++++
>  arch/x86/include/asm/x86_init.h |  2 ++
>  arch/x86/kernel/acpi/boot.c     |  5 +++++
>  arch/x86/kernel/x86_init.c      |  1 +
>  drivers/acpi/osl.c              | 14 +++++++++++++-
>  include/linux/acpi.h            |  6 ++++++
>  7 files changed, 49 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
> index 15255f388a85..149795c369f2 100644
> --- a/arch/x86/boot/compressed/acpi.c
> +++ b/arch/x86/boot/compressed/acpi.c
> @@ -26,7 +26,7 @@ struct mem_vector immovable_mem[MAX_NUMNODES*2];
>   */
>  #define MAX_ADDR_LEN 19
>  
> -static acpi_physical_address get_acpi_rsdp(void)
> +static acpi_physical_address get_cmdline_acpi_rsdp(void)
>  {
>  	acpi_physical_address addr = 0;
>  
> @@ -278,10 +278,7 @@ acpi_physical_address get_rsdp_addr(void)
>  {
>  	acpi_physical_address pa;
>  
> -	pa = get_acpi_rsdp();
> -
> -	if (!pa)
> -		pa = boot_params->acpi_rsdp_addr;

AFAICT, this looks like it would break current usage: get_rsdp_addr()
needs to call get_acpi_rsdp() which you've now called
get_cmdline_acpi_rsdp() to parse "acpi_rsdp=" but it ain't happening
anymore.

Where the parsing is happening now is in get_acpi_srat_table() which is
not present in configs with

#if defined(CONFIG_RANDOMIZE_BASE) && defined(CONFIG_MEMORY_HOTREMOVE)

false and thus not available to early code anymore.

I think the cleaner/easier approach would be to clear
boot_params->acpi_rsdp_addr after SRAT has been parsed in lockdown
configurations so that nothing else uses the supplied RDSP address
anymore. But I could very well be missing something...

Thx.
Borislav Petkov Aug. 14, 2019, 7:28 a.m. UTC | #3
On Wed, Aug 07, 2019 at 05:07:07PM -0700, 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. This requires some reworking
> of the existing RSDP command line logic, since the early boot code also
> makes use of a command-line passed RSDP when locating the SRAT table
> before the lockdown code has been initialised. This is achieved by
> separating the command line RSDP path in the early boot code from the
> generic RSDP path, and then copying the command line RSDP into boot
> params in the kernel proper if lockdown is not enabled. If lockdown is
> enabled and an RSDP is provided on the command line, this will only be
> used when parsing SRAT (which shouldn't permit kernel code execution)
> and will be ignored in the rest of the kernel.
> 
> (Modified by Matthew Garrett in order to handle the early boot RSDP
> environment)
> 
> 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
> ---
>  arch/x86/boot/compressed/acpi.c | 19 +++++++++++++------
>  arch/x86/include/asm/acpi.h     |  9 +++++++++
>  arch/x86/include/asm/x86_init.h |  2 ++
>  arch/x86/kernel/acpi/boot.c     |  5 +++++
>  arch/x86/kernel/x86_init.c      |  1 +
>  drivers/acpi/osl.c              | 14 +++++++++++++-
>  include/linux/acpi.h            |  6 ++++++
>  7 files changed, 49 insertions(+), 7 deletions(-)

Also, why isn't an x86 person CCed here? This clearly needs an x86
maintainer's ACK before it goes in?

Thx.
Matthew Garrett Aug. 14, 2019, 5:14 p.m. UTC | #4
On Wed, Aug 14, 2019 at 12:25 AM Borislav Petkov <bp@alien8.de> wrote:
> #if defined(CONFIG_RANDOMIZE_BASE) && defined(CONFIG_MEMORY_HOTREMOVE)
>
> false and thus not available to early code anymore.

We explicitly don't want to pay attention to the acpi_rsdp kernel
parameter in early boot except for the case of finding the SRAT table,
and we only need that if CONFIG_RANDOMIZE_BASE and
CONFIG_MEMORY_HOTREMOVE are set. However, we *do* want to tell the
actual kernel where the RSDP is if we found it via some other means,
so we can't just clear the boot parameters value. The kernel proper
will parse the command line again and will then (if lockdown isn't
enabled) override the actual value we passed up in boot params. So I
think this is ok?

(Sorry for not Cc:ing x86, clear oversight on my part)
Borislav Petkov Aug. 14, 2019, 5:47 p.m. UTC | #5
On Wed, Aug 14, 2019 at 10:14:54AM -0700, Matthew Garrett wrote:
> We explicitly don't want to pay attention to the acpi_rsdp kernel
> parameter in early boot except for the case of finding the SRAT table,
> and we only need that if CONFIG_RANDOMIZE_BASE and
> CONFIG_MEMORY_HOTREMOVE are set. However, we *do* want to tell the
> actual kernel where the RSDP is if we found it via some other means,
> so we can't just clear the boot parameters value.

Ok.

> The kernel proper will parse the command line again and will then (if
> lockdown isn't enabled) override the actual value we passed up in boot
> params.

Yeah, ok, I see what you're doing there. AFAICT, you do that in

setup_arch->acpi_boot_table_init-> ... -> acpi_os_get_root_pointer()

I hope nothing needs it earlier because then we'll have to restructure
again...

Thx.
Matthew Garrett Aug. 14, 2019, 6:02 p.m. UTC | #6
On Wed, Aug 14, 2019 at 10:46 AM Borislav Petkov <bp@alien8.de> wrote:
> Yeah, ok, I see what you're doing there. AFAICT, you do that in
>
> setup_arch->acpi_boot_table_init-> ... -> acpi_os_get_root_pointer()

Right.

> I hope nothing needs it earlier because then we'll have to restructure
> again...

Passing the RSDP via command line is a pretty grotesque hack - we
should just set up boot params in kexec_file, which would leave this
as a problem for legacy kexec and nothing else.

Patch
diff mbox series

diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index 15255f388a85..149795c369f2 100644
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -26,7 +26,7 @@  struct mem_vector immovable_mem[MAX_NUMNODES*2];
  */
 #define MAX_ADDR_LEN 19
 
-static acpi_physical_address get_acpi_rsdp(void)
+static acpi_physical_address get_cmdline_acpi_rsdp(void)
 {
 	acpi_physical_address addr = 0;
 
@@ -278,10 +278,7 @@  acpi_physical_address get_rsdp_addr(void)
 {
 	acpi_physical_address pa;
 
-	pa = get_acpi_rsdp();
-
-	if (!pa)
-		pa = boot_params->acpi_rsdp_addr;
+	pa = boot_params->acpi_rsdp_addr;
 
 	/*
 	 * Try to get EFI data from setup_data. This can happen when we're a
@@ -311,7 +308,17 @@  static unsigned long get_acpi_srat_table(void)
 	char arg[10];
 	u8 *entry;
 
-	rsdp = (struct acpi_table_rsdp *)(long)boot_params->acpi_rsdp_addr;
+	/*
+	 * Check whether we were given an RSDP on the command line. We don't
+	 * stash this in boot params because the kernel itself may have
+	 * different ideas about whether to trust a command-line parameter.
+	 */
+	rsdp = (struct acpi_table_rsdp *)get_cmdline_acpi_rsdp();
+
+	if (!rsdp)
+		rsdp = (struct acpi_table_rsdp *)(long)
+			boot_params->acpi_rsdp_addr;
+
 	if (!rsdp)
 		return 0;
 
diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index aac686e1e005..bc9693c9107e 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -117,6 +117,12 @@  static inline bool acpi_has_cpu_in_madt(void)
 	return !!acpi_lapic;
 }
 
+#define ACPI_HAVE_ARCH_SET_ROOT_POINTER
+static inline void acpi_arch_set_root_pointer(u64 addr)
+{
+	x86_init.acpi.set_root_pointer(addr);
+}
+
 #define ACPI_HAVE_ARCH_GET_ROOT_POINTER
 static inline u64 acpi_arch_get_root_pointer(void)
 {
@@ -125,6 +131,7 @@  static inline u64 acpi_arch_get_root_pointer(void)
 
 void acpi_generic_reduced_hw_init(void);
 
+void x86_default_set_root_pointer(u64 addr);
 u64 x86_default_get_root_pointer(void);
 
 #else /* !CONFIG_ACPI */
@@ -138,6 +145,8 @@  static inline void disable_acpi(void) { }
 
 static inline void acpi_generic_reduced_hw_init(void) { }
 
+static inline void x86_default_set_root_pointer(u64 addr) { }
+
 static inline u64 x86_default_get_root_pointer(void)
 {
 	return 0;
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index ac0934189017..19435858df5f 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -134,10 +134,12 @@  struct x86_hyper_init {
 
 /**
  * struct x86_init_acpi - x86 ACPI init functions
+ * @set_root_poitner:		set RSDP address
  * @get_root_pointer:		get RSDP address
  * @reduced_hw_early_init:	hardware reduced platform early init
  */
 struct x86_init_acpi {
+	void (*set_root_pointer)(u64 addr);
 	u64 (*get_root_pointer)(void);
 	void (*reduced_hw_early_init)(void);
 };
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 17b33ef604f3..04205ce127a1 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1760,6 +1760,11 @@  void __init arch_reserve_mem_area(acpi_physical_address addr, size_t size)
 	e820__update_table_print();
 }
 
+void x86_default_set_root_pointer(u64 addr)
+{
+	boot_params.acpi_rsdp_addr = addr;
+}
+
 u64 x86_default_get_root_pointer(void)
 {
 	return boot_params.acpi_rsdp_addr;
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index 1bef687faf22..18a799c8fa28 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -95,6 +95,7 @@  struct x86_init_ops x86_init __initdata = {
 	},
 
 	.acpi = {
+		.set_root_pointer	= x86_default_set_root_pointer,
 		.get_root_pointer	= x86_default_get_root_pointer,
 		.reduced_hw_early_init	= acpi_generic_reduced_hw_init,
 	},
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 9c0edf2fc0dd..d43df3a3fa8d 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>
@@ -180,8 +181,19 @@  acpi_physical_address __init acpi_os_get_root_pointer(void)
 	acpi_physical_address pa;
 
 #ifdef CONFIG_KEXEC
-	if (acpi_rsdp)
+	/*
+	 * We may have been provided with an RSDP on the command line,
+	 * but if a malicious user has done so they may be pointing us
+	 * at modified ACPI tables that could alter kernel behaviour -
+	 * so, we check the lockdown status before making use of
+	 * it. If we trust it then also stash it in an architecture
+	 * specific location (if appropriate) so it can be carried
+	 * over further kexec()s.
+	 */
+	if (acpi_rsdp && !security_locked_down(LOCKDOWN_ACPI_TABLES)) {
+		acpi_arch_set_root_pointer(acpi_rsdp);
 		return acpi_rsdp;
+	}
 #endif
 	pa = acpi_arch_get_root_pointer();
 	if (pa)
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index e40e1e27ed8e..6b35f2f4cab3 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -643,6 +643,12 @@  bool acpi_gtdt_c3stop(int type);
 int acpi_arch_timer_mem_init(struct arch_timer_mem *timer_mem, int *timer_count);
 #endif
 
+#ifndef ACPI_HAVE_ARCH_SET_ROOT_POINTER
+static inline void acpi_arch_set_root_pointer(u64 addr)
+{
+}
+#endif
+
 #ifndef ACPI_HAVE_ARCH_GET_ROOT_POINTER
 static inline u64 acpi_arch_get_root_pointer(void)
 {