linux-kernel - [tip:x86/urgent] x86/mm: Switch from TASK_SIZE to TASK_SIZE

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Date:	Fri, 20 May 2016 03:13:28 -0700
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	gorcunov@...il.com, brgerst@...il.com, peterz@...radead.org,
	bp@...en8.de, oleg@...hat.com, dvlasenk@...hat.com,
	luto@...capital.net, mingo@...nel.org, 0x7f454c46@...il.com,
	xemul@...allels.com, linux-kernel@...r.kernel.org, hpa@...or.com,
	luto@...nel.org, b7.10110111@...il.com,
	torvalds@...ux-foundation.org, tglx@...utronix.de
Subject: [tip:x86/urgent] x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in
 the page fault code

Commit-ID:  dc4fac84f8e66b147921ebdc385e767d5def7422
Gitweb:     http://git.kernel.org/tip/dc4fac84f8e66b147921ebdc385e767d5def7422
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Tue, 10 May 2016 14:10:29 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 20 May 2016 09:10:03 +0200

x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in the page fault code

x86's page fault handlers had two TASK_SIZE uses that should have
been TASK_SIZE_MAX.  I don't think that either one had a visible
effect, but this makes the code clearer and should save a few bytes
of text.

(And I eventually want to eradicate TASK_SIZE.  This will help.)

Reported-by: Cyrill Gorcunov <gorcunov@...il.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Dmitry Safonov <0x7f454c46@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Pavel Emelyanov <xemul@...allels.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ruslan Kabatsayev <b7.10110111@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1242fb23b0d05c3069dbf5758ac55d26bc114bef.1462914565.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/fault.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 5ce1ed0..7d1fa7c 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -292,7 +292,7 @@ void vmalloc_sync_all(void)
 		return;
 
 	for (address = VMALLOC_START & PMD_MASK;
-	     address >= TASK_SIZE && address < FIXADDR_TOP;
+	     address >= TASK_SIZE_MAX && address < FIXADDR_TOP;
 	     address += PMD_SIZE) {
 		struct page *page;
 
@@ -854,8 +854,13 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 				return;
 		}
 #endif
-		/* Kernel addresses are always protection faults: */
-		if (address >= TASK_SIZE)
+
+		/*
+		 * To avoid leaking information about the kernel page table
+		 * layout, pretend that user-mode accesses to kernel addresses
+		 * are always protection faults.
+		 */
+		if (address >= TASK_SIZE_MAX)
 			error_code |= PF_PROT;
 
 		if (likely(show_unhandled_signals))