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Message-Id: <20190318155139.963285969@infradead.org>
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Date:   Mon, 18 Mar 2019 16:38:41 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com,
        julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net,
        mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com,
        valentin.schneider@arm.com, brgerst@gmail.com, jpoimboe@redhat.com,
        luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        dvyukov@google.com, rostedt@goodmis.org
Subject: [PATCH 01/25] x86: Make SMAP 64-bit only
References: <20190318153840.906404905@infradead.org>
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We rely on objtool to verify AC=1 doesn't escape. However there is no
objtool support for x86_32, and thus we cannot guarantee the
correctness of the 32bit code.

Also; if you're running 32bit kernels on hardware with SMAP (which all
should have LM support afaik) you're doing it wrong anyway.

XXX: we could do the PUSHF/POPF thing in __switch_to_asm() on x86_32,
but why bother.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/Kconfig |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1853,6 +1853,8 @@ config ARCH_RANDOM
 
 config X86_SMAP
 	def_bool y
+	# Note: we rely on objtool to validate AC=1 doesn't escape
+	depends on HAVE_STACK_VALIDATION
 	prompt "Supervisor Mode Access Prevention" if EXPERT
 	---help---
 	  Supervisor Mode Access Prevention (SMAP) is a security