linux-kernel - [PATCH 3.16 121/131] x86/mm/kmmio: Make the tracer robust against L1TF

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Message-ID: <lsq.1538257387.543646646@decadent.org.uk>
Date:   Sat, 29 Sep 2018 22:43:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
        "Andi Kleen" <ak@...ux.intel.com>
Subject: [PATCH 3.16 121/131] x86/mm/kmmio: Make the tracer robust against
 L1TF

3.16.59-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Andi Kleen <ak@...ux.intel.com>

commit 1063711b57393c1999248cccb57bebfaf16739e7 upstream.

The mmio tracer sets io mapping PTEs and PMDs to non present when enabled
without inverting the address bits, which makes the PTE entry vulnerable
for L1TF.

Make it use the right low level macros to actually invert the address bits
to protect against L1TF.

In principle this could be avoided because MMIO tracing is not likely to be
enabled on production machines, but the fix is straigt forward and for
consistency sake it's better to get rid of the open coded PTE manipulation.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/mm/kmmio.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -114,24 +114,29 @@ static struct kmmio_fault_page *get_kmmi
 
 static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
 {
+	pmd_t new_pmd;
 	pmdval_t v = pmd_val(*pmd);
 	if (clear) {
-		*old = v & _PAGE_PRESENT;
-		v &= ~_PAGE_PRESENT;
-	} else	/* presume this has been called with clear==true previously */
-		v |= *old;
-	set_pmd(pmd, __pmd(v));
+		*old = v;
+		new_pmd = pmd_mknotpresent(*pmd);
+	} else {
+		/* Presume this has been called with clear==true previously */
+		new_pmd = __pmd(*old);
+	}
+	set_pmd(pmd, new_pmd);
 }
 
 static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
 {
 	pteval_t v = pte_val(*pte);
 	if (clear) {
-		*old = v & _PAGE_PRESENT;
-		v &= ~_PAGE_PRESENT;
-	} else	/* presume this has been called with clear==true previously */
-		v |= *old;
-	set_pte_atomic(pte, __pte(v));
+		*old = v;
+		/* Nothing should care about address */
+		pte_clear(&init_mm, 0, pte);
+	} else {
+		/* Presume this has been called with clear==true previously */
+		set_pte_atomic(pte, __pte(*old));
+	}
 }
 
 static int clear_page_presence(struct kmmio_fault_page *f, bool clear)