linux-kernel - [PATCH 4.1 31/65] kaiser: KAISER depends on SMP

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Date:   Mon,  5 Mar 2018 19:25:04 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, Alexander.Levin@...rosoft.com,
        dan.j.williams@...el.com, sathyanarayanan.kuppuswamy@...el.com,
        pankaj.laxminarayan.bharadiya@...el.com, akuster@...sta.com,
        cminyard@...sta.com, pasha.tatashin@...cle.com,
        gregkh@...uxfoundation.org, stable@...r.kernel.org
Subject: [PATCH 4.1 31/65] kaiser: KAISER depends on SMP

From: Hugh Dickins <hughd@...gle.com>

It is absurd that KAISER should depend on SMP, but apparently nobody
has tried a UP build before: which breaks on implicit declaration of
function 'per_cpu_offset' in arch/x86/mm/kaiser.c.

Now, you would expect that to be trivially fixed up; but looking at
the System.map when that block is #ifdef'ed out of kaiser_init(),
I see that in a UP build __per_cpu_user_mapped_end is precisely at
__per_cpu_user_mapped_start, and the items carefully gathered into
that section for user-mapping on SMP, dispersed elsewhere on UP.

So, some other kind of section assignment will be needed on UP,
but implementing that is not a priority: just make KAISER depend
on SMP for now.

Also inserted a blank line before the option, tidied up the
brief Kconfig help message, and added an "If unsure, Y".

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Acked-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
(cherry picked from commit d94df20135ccfdfb77b1479c501564e9b4ab5bc9)
Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
 security/Kconfig | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/security/Kconfig b/security/Kconfig
index cdad6dd3693a..5f4b656bfa4c 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -30,14 +30,16 @@ config SECURITY
 	  model will be used.

 	  If you are unsure how to answer this question, answer N.
+
 config KAISER
 	bool "Remove the kernel mapping in user mode"
 	default y
-	depends on X86_64
-	depends on !PARAVIRT
+	depends on X86_64 && SMP && !PARAVIRT
 	help
-	  This enforces a strict kernel and user space isolation in order to close
-	  hardware side channels on kernel address information.
+	  This enforces a strict kernel and user space isolation, in order
+	  to close hardware side channels on kernel address information.
+
+	  If you are unsure how to answer this question, answer Y.

 config KAISER_REAL_SWITCH
 	bool "KAISER: actually switch page tables"
-- 
2.16.2