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* [PATCH] x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in the page fault code
@ 2016-05-10 21:10 Andy Lutomirski
  2016-05-20 10:13 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
  0 siblings, 1 reply; 2+ messages in thread
From: Andy Lutomirski @ 2016-05-10 21:10 UTC (permalink / raw)
  To: x86
  Cc: Cyrill Gorcunov, Dmitry Safonov, Ruslan Kabatsayev,
	Borislav Petkov, Pavel Emelyanov, Oleg Nesterov, linux-kernel,
	Andy Lutomirski

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@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.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 1d75b98a8414..45940239b983 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))
-- 
2.5.5

^ permalink raw reply related	[flat|nested] 2+ messages in thread

* [tip:x86/urgent] x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in the page fault code
  2016-05-10 21:10 [PATCH] x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in the page fault code Andy Lutomirski
@ 2016-05-20 10:13 ` tip-bot for Andy Lutomirski
  0 siblings, 0 replies; 2+ messages in thread
From: tip-bot for Andy Lutomirski @ 2016-05-20 10:13 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: gorcunov, brgerst, peterz, bp, oleg, dvlasenk, luto, mingo,
	0x7f454c46, xemul, linux-kernel, hpa, luto, b7.10110111,
	torvalds, tglx

Commit-ID:  dc4fac84f8e66b147921ebdc385e767d5def7422
Gitweb:     http://git.kernel.org/tip/dc4fac84f8e66b147921ebdc385e767d5def7422
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Tue, 10 May 2016 14:10:29 -0700
Committer:  Ingo Molnar <mingo@kernel.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@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ruslan Kabatsayev <b7.10110111@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1242fb23b0d05c3069dbf5758ac55d26bc114bef.1462914565.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.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))

^ permalink raw reply related	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2016-05-20 10:14 UTC | newest]

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2016-05-10 21:10 [PATCH] x86/mm: Switch from TASK_SIZE to TASK_SIZE_MAX in the page fault code Andy Lutomirski
2016-05-20 10:13 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski

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