[PATCH V40 15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down
Rafael J. Wysocki
rjw at rjwysocki.net
Tue Aug 20 22:08:18 UTC 2019
On Tuesday, August 20, 2019 2:17:51 AM CEST Matthew Garrett wrote:
> From: Josh Boyer <jwboyer at 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 at redhat.com>
> Signed-off-by: David Howells <dhowells at redhat.com>
> Signed-off-by: Matthew Garrett <mjg59 at google.com>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> cc: Dave Young <dyoung at redhat.com>
> cc: linux-acpi at vger.kernel.org
> Signed-off-by: James Morris <jmorris at namei.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
> ---
> 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 ad84239e595e..e726e9b44bb1 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;
>
> @@ -215,10 +215,7 @@ 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;
>
> if (!pa)
> pa = efi_get_rsdp_addr();
> @@ -240,7 +237,17 @@ 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 b85a7c54c6a1..d584128435cb 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 50a2b492fdd6..d0b8f5585a73 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 cc7507091dec..b7c3aeb175dd 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 d315d86844e4..268a4d91f54c 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -632,6 +632,12 @@ 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)
> {
>
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