diff options
| author | Daniel Sneddon | 2022-08-16 16:19:42 -0700 |
|---|---|---|
| committer | Dave Hansen | 2022-08-31 14:34:11 -0700 |
| commit | b8d1d163604bd1e600b062fb00de5dc42baa355f (patch) | |
| tree | f60d9b0c43b85ada45f517eb5735b48caae850b4 /arch/x86/Kconfig | |
| parent | b90cb1053190353cc30f0fef0ef1f378ccc063c5 (diff) | |
x86/apic: Don't disable x2APIC if locked
The APIC supports two modes, legacy APIC (or xAPIC), and Extended APIC
(or x2APIC). X2APIC mode is mostly compatible with legacy APIC, but
it disables the memory-mapped APIC interface in favor of one that uses
MSRs. The APIC mode is controlled by the EXT bit in the APIC MSR.
The MMIO/xAPIC interface has some problems, most notably the APIC LEAK
[1]. This bug allows an attacker to use the APIC MMIO interface to
extract data from the SGX enclave.
Introduce support for a new feature that will allow the BIOS to lock
the APIC in x2APIC mode. If the APIC is locked in x2APIC mode and the
kernel tries to disable the APIC or revert to legacy APIC mode a GP
fault will occur.
Introduce support for a new MSR (IA32_XAPIC_DISABLE_STATUS) and handle
the new locked mode when the LEGACY_XAPIC_DISABLED bit is set by
preventing the kernel from trying to disable the x2APIC.
On platforms with the IA32_XAPIC_DISABLE_STATUS MSR, if SGX or TDX are
enabled the LEGACY_XAPIC_DISABLED will be set by the BIOS. If
legacy APIC is required, then it SGX and TDX need to be disabled in the
BIOS.
[1]: https://aepicleak.com/aepicleak.pdf
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Link: https://lkml.kernel.org/r/20220816231943.1152579-1-daniel.sneddon@linux.intel.com
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f9920f1341c8..159c025ebb03 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -448,6 +448,11 @@ config X86_X2APIC This allows 32-bit apic IDs (so it can support very large systems), and accesses the local apic via MSRs not via mmio. + Some Intel systems circa 2022 and later are locked into x2APIC mode + and can not fall back to the legacy APIC modes if SGX or TDX are + enabled in the BIOS. They will be unable to boot without enabling + this option. + If you don't know what to do here, say N. config X86_MPPARSE @@ -1919,7 +1924,7 @@ endchoice config X86_SGX bool "Software Guard eXtensions (SGX)" - depends on X86_64 && CPU_SUP_INTEL + depends on X86_64 && CPU_SUP_INTEL && X86_X2APIC depends on CRYPTO=y depends on CRYPTO_SHA256=y select SRCU |