Re: [RFC PATCH v2 05/11] x86/power: Restore Key Locker internal key from the ACPI S3/4 sleep states

From: Rafael J. Wysocki
Date: Mon May 24 2021 - 10:21:38 EST

On Fri, May 14, 2021 at 10:20 PM Chang S. Bae <chang.seok.bae@xxxxxxxxx> wrote:
>
> When the system state switches to these sleep states, the internal key gets
> reset. Since this system transition is transparent to userspace, the
> internal key needs to be restored properly.
>
> Key Locker provides a mechanism to back up the internal key in non-volatile
> memory. The kernel requests a backup right after the key loaded at
> boot-time and copies it later when the system wakes up.
>
> The backup during the S5 sleep state is not trusted. It is overwritten by a
> new key at the next boot.
>
> On a system with the S3/4 states, enable the feature only when the backup
> mechanism is supported.
>
> Disable the feature when the copy fails (or the backup corrupts). The
> shutdown is considered too noisy. A new key is considerable only when
> threads can be synchronously suspended.
>
> Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-pm@xxxxxxxxxxxxxxx

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
> Changes from RFC v1:
> * Folded the warning message into the if condition check. (Rafael Wysocki)
> * Rebased on the changes of the previous patches.
> * Added error code for key restoration failures.
> * Moved the restore helper.
> * Added function descriptions.
> ---
> arch/x86/include/asm/keylocker.h | 3 +
> arch/x86/kernel/keylocker.c | 122 +++++++++++++++++++++++++++++--
> arch/x86/power/cpu.c | 2 +
> 3 files changed, 122 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/keylocker.h b/arch/x86/include/asm/keylocker.h
> index 870832f007ec..74b806346bee 100644
> --- a/arch/x86/include/asm/keylocker.h
> +++ b/arch/x86/include/asm/keylocker.h
> @@ -7,6 +7,7 @@
>
> #include <asm/processor.h>
> #include <linux/bits.h>
> +#include <asm/msr.h>
>
> #define KEYLOCKER_CPUID 0x019
> #define KEYLOCKER_CPUID_EAX_SUPERVISOR BIT(0)
> @@ -18,9 +19,11 @@
> #ifdef CONFIG_X86_KEYLOCKER
> void setup_keylocker(struct cpuinfo_x86 *c);
> void flush_keylocker_data(void);
> +void restore_keylocker(void);
> #else
> #define setup_keylocker(c) do { } while (0)
> #define flush_keylocker_data() do { } while (0)
> +#define restore_keylocker() do { } while (0)
> #endif
>
> #endif /*__ASSEMBLY__ */
> diff --git a/arch/x86/kernel/keylocker.c b/arch/x86/kernel/keylocker.c
> index d590815de508..0f60350944fa 100644
> --- a/arch/x86/kernel/keylocker.c
> +++ b/arch/x86/kernel/keylocker.c
> @@ -5,6 +5,8 @@
> */
>
> #include <linux/random.h>
> +#include <linux/acpi.h>
> +#include <linux/delay.h>
>
> #include <asm/cacheflush.h>
> #include <asm/fpu/api.h>
> @@ -12,10 +14,13 @@
> #include <asm/keylocker.h>
> #include <asm/tlbflush.h>
>
> +static bool keybackup_available;
> +
> /* Internal (Wrapping) Key size fits in three 128-bit registers. */
> #define KEYSIZE_128BIT 3
>
> static struct _keydata {
> + bool valid;
> struct reg_128_bit value[KEYSIZE_128BIT];
> } keydata;
>
> @@ -30,6 +35,8 @@ static void make_keylocker_data(void)
>
> for (i = 0; i < KEYSIZE_128BIT; i++)
> get_random_bytes(&keydata.value[i], sizeof(struct reg_128_bit));
> +
> + keydata.valid = true;
> }
>
> /**
> @@ -47,6 +54,8 @@ void flush_keylocker_data(void)
>
> memset(keyaddr, 0, size);
> clflush_cache_range(keyaddr, size);
> +
> + keydata.valid = false;
> }
>
> #define KEYSRC_SWRAND 0
> @@ -79,6 +88,40 @@ static int load_keylocker(void)
> return err;
> }
>
> +#define KEYRESTORE_RETRY 1
> +
> +/**
> + * copy_keylocker() - Copy the internal key from the backup.
> + *
> + * Request hardware to copy the key in non-volatile memory to the CPU state. Do this
> + * again if the copy fails. The key may not be ready when the precedent backup is
> + * still in progress.
> + *
> + * Returns: -EBUSY if the copy fails, -ENODEV if no backup is available, or 0 if
> + * successful.
> + */
> +static int copy_keylocker(void)
> +{
> + int i;
> +
> + if (!keybackup_available)
> + return -ENODEV;
> +
> + wrmsrl(MSR_IA32_COPY_PLATFORM_TO_LOCAL, 1);
> +
> + for (i = 0; i <= KEYRESTORE_RETRY; i++) {
> + u64 status;
> +
> + if (i)
> + udelay(1);
> +
> + rdmsrl(MSR_IA32_COPY_STATUS, status);
> + if (status & BIT(0))
> + return 0;
> + }
> + return -EBUSY;
> +}
> +
> /**
> * setup_keylocker() - Enable the feature if supported.
> * @c: A pointer to struct cpuinfo_x86
> @@ -104,13 +147,43 @@ void setup_keylocker(struct cpuinfo_x86 *c)
> goto disable;
> }
>
> + keybackup_available = (ebx & KEYLOCKER_CPUID_EBX_BACKUP);
> + /* Internal key backup is essential with S3/4 states. */
> + if (!keybackup_available &&
> + (acpi_sleep_state_supported(ACPI_STATE_S3) ||
> + acpi_sleep_state_supported(ACPI_STATE_S4))) {
> + pr_debug("x86/keylocker: no key backup support with possible S3/4.\n");
> + goto disable;
> + }
> +
> make_keylocker_data();
> - }
>
> - err = load_keylocker();
> - if (err) {
> - pr_err_once("x86/keylocker: Failed to load internal key (rc: %d).\n", err);
> - goto disable;
> + err = load_keylocker();
> + if (err) {
> + pr_err_once("x86/keylocker: Failed to load internal key (rc: %d).\n", err);
> + goto disable;
> + }
> +
> + /* Back up the internal key in non-volatile memory if supported. */
> + if (keybackup_available)
> + wrmsrl(MSR_IA32_COPY_LOCAL_TO_PLATFORM, 1);
> + } else {
> +
> + /*
> + * Load the internal key directly when available in memory, which is only
> + * possible at boot-time.
> + *
> + * NB: When system wakes up, this path also recovers the internal key.
> + */
> + if (keydata.valid)
> + err = load_keylocker();
> + else
> + err = copy_keylocker();
> + if (err) {
> + pr_err_once("x86/keylocker: Fail to %s internal key (rc: %d).\n",
> + keydata.valid ? "load" : "copy", err);
> + goto disable;
> + }
> }
>
> pr_info_once("x86/keylocker: Enabled.\n");
> @@ -123,3 +196,42 @@ void setup_keylocker(struct cpuinfo_x86 *c)
> /* Make sure the feature disabled for kexec-reboot. */
> cr4_clear_bits(X86_CR4_KEYLOCKER);
> }
> +
> +/**
> + * restore_keylocker() - Restore the internal key.
> + *
> + * The boot CPU executes this while other CPUs restore it through the setup function.
> + *
> + * Returns: Nothing
> + */
> +void restore_keylocker(void)
> +{
> + u64 backup_status;
> + int err;
> +
> + if (!boot_cpu_has(X86_FEATURE_KEYLOCKER))
> + return;
> +
> + /*
> + * IA32_IWKEYBACKUP_STATUS MSR contains a bitmap that indicates an invalid backup if bit 0
> + * is set and a read (or write) error if bit 2 is set.
> + */
> + rdmsrl(MSR_IA32_IWKEYBACKUP_STATUS, backup_status);
> + if (WARN(!(backup_status & BIT(0)),
> + "x86/keylocker: Internal key backup access failed with %s.\n",
> + (backup_status & BIT(2)) ? "read error" : "invalid status"))
> + goto disable_out;
> +
> + err = copy_keylocker();
> + if (err) {
> + pr_err("x86/keylocker: Internal key restoration failed (rc: %d).\n", err);
> + goto disable_out;
> + }
> +
> + return;
> +
> +disable_out:
> + pr_info("x86/keylocker: Disabled with internal key restoration failure.\n");
> + setup_clear_cpu_cap(X86_FEATURE_KEYLOCKER);
> + cr4_clear_bits(X86_CR4_KEYLOCKER);
> +}
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 3a070e7cdb8b..ace94f07701a 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -25,6 +25,7 @@
> #include <asm/cpu.h>
> #include <asm/mmu_context.h>
> #include <asm/cpu_device_id.h>
> +#include <asm/keylocker.h>
>
> #ifdef CONFIG_X86_32
> __visible unsigned long saved_context_ebx;
> @@ -261,6 +262,7 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
> mtrr_bp_restore();
> perf_restore_debug_store();
> msr_restore_context(ctxt);
> + restore_keylocker();
>
> c = &cpu_data(smp_processor_id());
> if (cpu_has(c, X86_FEATURE_MSR_IA32_FEAT_CTL))
> --
> 2.17.1
>