linux-kernel - [PATCH 3.16 098/131] x86/speculation/l1tf: Make sure the first page is always reserved

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Message-ID: <lsq.1538257387.652856432@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, "Dave Hansen" <dave.hansen@...el.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        "Andi Kleen" <ak@...ux.intel.com>
Subject: [PATCH 3.16 098/131] x86/speculation/l1tf: Make sure the first
 page is always reserved

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

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

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

commit 10a70416e1f067f6c4efda6ffd8ea96002ac4223 upstream.

The L1TF workaround doesn't make any attempt to mitigate speculate accesses
to the first physical page for zeroed PTEs. Normally it only contains some
data from the early real mode BIOS.

It's not entirely clear that the first page is reserved in all
configurations, so add an extra reservation call to make sure it is really
reserved. In most configurations (e.g.  with the standard reservations)
it's likely a nop.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
Acked-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/setup.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -860,6 +860,12 @@ void __init setup_arch(char **cmdline_p)
 	memblock_reserve(__pa_symbol(_text),
 			 (unsigned long)__bss_stop - (unsigned long)_text);
 
+	/*
+	 * Make sure page 0 is always reserved because on systems with
+	 * L1TF its contents can be leaked to user processes.
+	 */
+	memblock_reserve(0, PAGE_SIZE);
+
 	early_reserve_initrd();
 
 	/*