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Subject[PATCH 4.9 09/39] kaiser: KAISER depends on SMP
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@google.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@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
security/Kconfig | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- 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"

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