[PATCH v7 05/12] x86/msr-index: Add MSRs for Key Locker wrapping key

From: Chang S. Bae
Date: Wed May 24 2023 - 13:10:57 EST

The CPU state that contains the wrapping key is in the same power
domain as the cache. So any sleep state that would invalidate the
cache (like S3) also invalidates the state of the wrapping key.

But, since the state is inaccessible to software, it needs a special
mechanism to save and restore the key during deep sleep.

A set of new MSRs are provided as an abstract interface to save and
restore the wrapping key, and to check the key status. The wrapping
key is saved in a platform-scoped state of non-volatile media. The
backup itself and its path from the CPU are encrypted and integrity

Define those MSRs to be used to save and restore the key for S3/4
sleep states.

But the backup storage's non-volatility is not architecturally
guaranteed across off-states, such as S5 and G3. Then, the kernel may
generate a new key on the next boot.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Changes from v6:
* Tweak the changelog -- put the last for those about other sleep

Changes from RFC v2:
* Update the changelog. (Dan Williams)
* Rename the MSRs. (Dan Williams)
arch/x86/include/asm/msr-index.h | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 3aedae61af4f..cd8555c0f3c2 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -1117,4 +1117,10 @@
* a #GP

+/* MSRs for managing a CPU-internal wrapping key for Key Locker. */
+#define MSR_IA32_IWKEY_COPY_STATUS 0x00000990
+#define MSR_IA32_IWKEY_BACKUP_STATUS 0x00000991
+#define MSR_IA32_BACKUP_IWKEY_TO_PLATFORM 0x00000d91
+#define MSR_IA32_COPY_IWKEY_TO_LOCAL 0x00000d92
#endif /* _ASM_X86_MSR_INDEX_H */