linux-kernel - [PATCH 1/2] x86, pti: fix boot problems from Global-bit setting

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Date:   Tue, 17 Apr 2018 14:13:02 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        mceier@...il.com, aaro.koskinen@...ia.com, aarcange@...hat.com,
        luto@...nel.org, arjan@...ux.intel.com, bp@...en8.de,
        dan.j.williams@...el.com, dwmw2@...radead.org,
        gregkh@...uxfoundation.org, hughd@...gle.com, jpoimboe@...hat.com,
        jgross@...e.com, keescook@...gle.com,
        torvalds@...ux-foundation.org, namit@...are.com,
        peterz@...radead.org, tglx@...utronix.de
Subject: [PATCH 1/2] x86, pti: fix boot problems from Global-bit setting


These are _very_ lightly tested.  I'm throwing them out there for
folks are looking for a fix.

---

From: Dave Hansen <dave.hansen@...ux.intel.com>

Part of the global bit _setting_ patches also includes clearing the
Global bit when we do not want it.  That is done with
set_memory_nonglobal(), which uses change_page_attr_clear() in
pageattr.c under the covers.  However, it's pretty clear that
change_page_attr_clear() has not been heavily used early in boot, or
on kernel text.

It has checks like BUG_ON(irqs_disabled()), looking for interrupt
disabling but that also trip in early boot on certain preempt
configurations.  Just copy the existing BUG_ON() sequence to check for
early boot.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Fixes: 39114b7a7 (x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image)
Reported-by: Mariusz Ceier <mceier@...il.com>
Reported-by: Aaro Koskinen <aaro.koskinen@...ia.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Kees Cook <keescook@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nadav Amit <namit@...are.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org
---

 b/arch/x86/mm/pageattr.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN arch/x86/mm/pageattr.c~pti-glb-boot-problem-fix arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~pti-glb-boot-problem-fix	2018-04-17 14:10:13.553395577 -0700
+++ b/arch/x86/mm/pageattr.c	2018-04-17 14:10:13.559395577 -0700
@@ -172,7 +172,7 @@ static void __cpa_flush_all(void *arg)
 
 static void cpa_flush_all(unsigned long cache)
 {
-	BUG_ON(irqs_disabled());
+	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
 
 	on_each_cpu(__cpa_flush_all, (void *) cache, 1);
 }
@@ -236,7 +236,7 @@ static void cpa_flush_array(unsigned lon
 	unsigned long do_wbinvd = cache && numpages >= 1024; /* 4M threshold */
 #endif
 
-	BUG_ON(irqs_disabled());
+	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
 
 	on_each_cpu(__cpa_flush_all, (void *) do_wbinvd, 1);
 
_