linux-kernel - [PATCH v10 07/27] x86/fpu/xstate: Warn if kernel dynamic xfeatures detected in normal fpstate

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Date: Sun, 18 Feb 2024 23:47:13 -0800
From: Yang Weijiang <weijiang.yang@...el.com>
To: seanjc@...gle.com,
	pbonzini@...hat.com,
	dave.hansen@...el.com,
	x86@...nel.org,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: peterz@...radead.org,
	chao.gao@...el.com,
	rick.p.edgecombe@...el.com,
	mlevitsk@...hat.com,
	john.allen@....com,
	weijiang.yang@...el.com
Subject: [PATCH v10 07/27] x86/fpu/xstate: Warn if kernel dynamic xfeatures detected in normal fpstate

Kernel dynamic xfeatures now are __ONLY__ enabled for guest fpstate, i.e.,
never for normal kernel fpstate. The bits are added when guest FPU config
is initialized. Guest fpstate is allocated with fpstate->is_guest set to
%true.

For normal fpstate, the bits should have been removed when initializes
kernel FPU config settings, WARN_ONCE() if kernel detects normal fpstate
xfeatures contains kernel dynamic xfeatures before executes xsaves.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kernel/fpu/xstate.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 3518fb26d06b..83ebf1e1cbb4 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -185,6 +185,9 @@ static inline void os_xsave(struct fpstate *fpstate)
 	WARN_ON_FPU(!alternatives_patched);
 	xfd_validate_state(fpstate, mask, false);
 
+	WARN_ON_FPU(!fpstate->is_guest &&
+		    (mask & XFEATURE_MASK_KERNEL_DYNAMIC));
+
 	XSTATE_XSAVE(&fpstate->regs.xsave, lmask, hmask, err);
 
 	/* We should never fault when copying to a kernel buffer: */
-- 
2.43.0