linux-kernel - [PATCH 4.14 140/146] x86/mm: Remove preempt_disable/enable() from __native_flush

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20180101140144.012399442@linuxfoundation.org>
Date:   Mon,  1 Jan 2018 15:38:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.14 140/146] x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()

4.14-stable review patch.  If anyone has any objections, please let me know.

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

From: Thomas Gleixner <tglx@...utronix.de>

commit decab0888e6e14e11d53cefa85f8b3d3b45ce73c upstream.

The preempt_disable/enable() pair in __native_flush_tlb() was added in
commit:

  5cf0791da5c1 ("x86/mm: Disable preemption during CR3 read+write")

... to protect the UP variant of flush_tlb_mm_range().

That preempt_disable/enable() pair should have been added to the UP variant
of flush_tlb_mm_range() instead.

The UP variant was removed with commit:

  ce4a4e565f52 ("x86/mm: Remove the UP asm/tlbflush.h code, always use the (formerly) SMP code")

... but the preempt_disable/enable() pair stayed around.

The latest change to __native_flush_tlb() in commit:

  6fd166aae78c ("x86/mm: Use/Fix PCID to optimize user/kernel switches")

... added an access to a per CPU variable outside the preempt disabled
regions, which makes no sense at all. __native_flush_tlb() must always
be called with at least preemption disabled.

Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch
bad callers independent of the smp_processor_id() debugging.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/20171230211829.679325424@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/asm/tlbflush.h |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -345,15 +345,17 @@ static inline void invalidate_user_asid(
  */
 static inline void __native_flush_tlb(void)
 {
-	invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
 	/*
-	 * If current->mm == NULL then we borrow a mm which may change
-	 * during a task switch and therefore we must not be preempted
-	 * while we write CR3 back:
+	 * Preemption or interrupts must be disabled to protect the access
+	 * to the per CPU variable and to prevent being preempted between
+	 * read_cr3() and write_cr3().
 	 */
-	preempt_disable();
+	WARN_ON_ONCE(preemptible());
+
+	invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
+
+	/* If current->mm == NULL then the read_cr3() "borrows" an mm */
 	native_write_cr3(__native_read_cr3());
-	preempt_enable();
 }
 
 /*