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 <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ruslan Kabatsayev <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/1242fb23b0d05c3069dbf5758ac55d26bc114bef.1462914565.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 5ce1ed02f7e80900ead34c8b8af2bfe223a9d3bd..7d1fa7cd237443e054da06255697412d5e9354f6 100644 (file)
--- 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))