linux-kernel - [PATCH 01/25] x86: Make SMAP 64-bit only

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Date:   Mon, 18 Mar 2019 16:38:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, jpoimboe@...hat.com,
        luto@...nel.org, bp@...en8.de, dvlasenk@...hat.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: [PATCH 01/25] x86: Make SMAP 64-bit only

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@...radead.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