From ea68e39190cff86f457bd286c70b535e2a99a94d Mon Sep 17 00:00:00 2001 From: "Chang S. Bae" Date: Tue, 15 Apr 2025 19:16:53 -0700 Subject: [PATCH] x86/fpu/apx: Disallow conflicting MPX presence XSTATE components are architecturally independent. There is no rule requiring their offsets in the non-compacted format to be strictly ascending or mutually non-overlapping. However, in practice, such overlaps have not occurred -- until now. APX is introduced as xstate component 19, following AMX. In the non-compacted XSAVE format, its offset overlaps with the space previously occupied by the now-deprecated MPX feature: 45fc24e89b7c ("x86/mpx: remove MPX from arch/x86") To prevent conflicts, the kernel must ensure the CPU never expose both features at the same time. If so, it indicates unreliable hardware. In such cases, XSAVE should be disabled entirely as a precautionary measure. Add a sanity check to detect this condition and disable XSAVE if an invalid hardware configuration is identified. Note: MPX state components remain enabled on legacy systems solely for KVM guest support. Signed-off-by: Chang S. Bae Signed-off-by: Ingo Molnar Reviewed-by: Sohil Mehta Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Link: https://lore.kernel.org/r/20250416021720.12305-4-chang.seok.bae@intel.com --- arch/x86/kernel/fpu/xstate.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index dfd07af100374..14f5c1bb20800 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -814,6 +814,17 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) goto out_disable; } + if (fpu_kernel_cfg.max_features & XFEATURE_MASK_APX && + fpu_kernel_cfg.max_features & (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR)) { + /* + * This is a problematic CPU configuration where two + * conflicting state components are both enumerated. + */ + pr_err("x86/fpu: Both APX/MPX present in the CPU's xstate features: 0x%llx, disabling XSAVE.\n", + fpu_kernel_cfg.max_features); + goto out_disable; + } + fpu_kernel_cfg.independent_features = fpu_kernel_cfg.max_features & XFEATURE_MASK_INDEPENDENT; -- 2.47.3