linux-kernel - [PATCH] x86/fpu: Warn only when CPU-provided sizes less than struct declaration

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Date:   Tue,  3 Dec 2019 04:01:28 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        jon.grimm@....com,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Lendacky <Thomas.Lendacky@....com>
Subject: [PATCH] x86/fpu: Warn only when CPU-provided sizes less than struct declaration

The current XCHECK_SZ macro warns if the XFEATURE size reported
by CPUID does not match the size of kernel structure. However, depending
on the hardware implementation, CPUID can report the XSAVE state size
larger than the size of C structures defined for each of the XSAVE state
due to padding. Such case should be safe and should not need to generate
warning message.

Therefore, change the logic to warn only when the CPUID reported size is
less than then size of C structure.

Fixes: ef78f2a4bf84 ("x86/fpu: Check CPU-provided sizes against struct declarations")
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Thomas Lendacky <Thomas.Lendacky@....com> 
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kernel/fpu/xstate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index e5cb67d..f002115 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -523,7 +523,7 @@ static void __xstate_dump_leaves(void)
 
 #define XCHECK_SZ(sz, nr, nr_macro, __struct) do {			\
 	if ((nr == nr_macro) &&						\
-	    WARN_ONCE(sz != sizeof(__struct),				\
+	    WARN_ONCE(sz < sizeof(__struct),				\
 		"%s: struct is %zu bytes, cpu state %d bytes\n",	\
 		__stringify(nr_macro), sizeof(__struct), sz)) {		\
 		__xstate_dump_leaves();					\
-- 
1.8.3.1