[PATCH] MIPS: Make TASK_SIZE reflect proper size for both 32 and 64 bit processes.

[David Daney <ddaney@caviumnetworks.com>]

The TASK_SIZE macro should reflect the size of a user process virtual
address space.  Previously for 64-bit kernels, this was not the case.
The immediate cause of pain was in
hugetlbfs/inode.c:hugetlb_get_unmapped_area() where 32-bit processes
trying to mmap a huge page would be served a page with an address
outside of the 32-bit address range.  But there are other uses of
TASK_SIZE in the kernel as well that would like an accurate value.

The new definition is nice because it now makes TASK_SIZE and
TASK_SIZE_OF() yield the same value for any given process.

For 32-bit kernels there should be no change, although I did factor
out some code in asm/processor.h that became identical for the 32-bit and
64-bit cases.

Another, perhaps non-obvious, change is that in 64-bit kernels, the
get_fs() value (A.K.A current_thread_info()->addr_limit) will now vary
depending on the address space size of the process.  This is a change,
as previously even 32-bit processes would have an addr_limit
appropriate for a 64-bit process.  This will change the behavior of
access_ok(), but I think the new behavior is desirable.

Before the patch it may have been possible for a user space process to
pass a pointer to the kernel that would pass the access_ok() check,
but be outside of the 32-bit address space.

With the patch applied, I can still run o32, n32 and n64 processes,
and have an o32 shell fork/exec both n32 and n64 processes.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
---
 arch/mips/include/asm/elf.h        |    1 +
 arch/mips/include/asm/pgtable-64.h |    4 +-
 arch/mips/include/asm/processor.h  |   40 +++++++++++++++++------------------
 arch/mips/include/asm/uaccess.h    |    3 +-
 4 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index fd1d39e..ca8cb9f 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -306,6 +306,7 @@ do {                                                        
                \
                                                                        \
        if (current->personality != PER_LINUX32)                        \
                set_personality(PER_LINUX);                             \
+       set_fs(USER_DS); /* Update addr_limit for TIF_32BIT_ADDR. */    \
 } while (0)
 
 #endif /* CONFIG_64BIT */
diff --git a/arch/mips/include/asm/pgtable-64.h 
b/arch/mips/include/asm/pgtable-64.h
index 1be4b0f..82d881a 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -113,10 +113,10 @@
 #endif
 #define PTRS_PER_PTE   ((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t))
 
-#if PGDIR_SIZE >= TASK_SIZE
+#if PGDIR_SIZE >= TASK_SIZE64
 #define USER_PTRS_PER_PGD       (1)
 #else
-#define USER_PTRS_PER_PGD      (TASK_SIZE / PGDIR_SIZE)
+#define USER_PTRS_PER_PGD      (TASK_SIZE64 / PGDIR_SIZE)
 #endif
 #define FIRST_USER_ADDRESS     0UL
 
diff --git a/arch/mips/include/asm/processor.h 
b/arch/mips/include/asm/processor.h
index 0d629bb..ead6928 100644
--- a/arch/mips/include/asm/processor.h
+++ b/arch/mips/include/asm/processor.h
@@ -50,13 +50,10 @@ extern unsigned int vced_count, vcei_count;
  * so don't change it unless you know what you are doing.
  */
 #define TASK_SIZE      0x7fff8000UL
-#define STACK_TOP      ((TASK_SIZE & PAGE_MASK) - SPECIAL_PAGES_SIZE)
 
-/*
- * This decides where the kernel will search for a free chunk of vm
- * space during mmap's.
- */
-#define TASK_UNMAPPED_BASE     ((TASK_SIZE / 3) & ~(PAGE_SIZE))
+#ifdef __KERNEL__
+#define STACK_TOP_MAX  TASK_SIZE
+#endif
 
 #define TASK_IS_32BIT_ADDR 1
 
@@ -71,28 +68,29 @@ extern unsigned int vced_count, vcei_count;
  * 8192EB ...
  */
 #define TASK_SIZE32    0x7fff8000UL
-#define TASK_SIZE      0x10000000000UL
-#define STACK_TOP      \
-       (((test_thread_flag(TIF_32BIT_ADDR) ?                           \
-          TASK_SIZE32 : TASK_SIZE) & PAGE_MASK) - SPECIAL_PAGES_SIZE)
+#define TASK_SIZE64    0x10000000000UL
+#define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 : 
TASK_SIZE64)
+
+#ifdef __KERNEL__
+#define STACK_TOP_MAX  TASK_SIZE64
+#endif
+
 
-/*
- * This decides where the kernel will search for a free chunk of vm
- * space during mmap's.
- */
-#define TASK_UNMAPPED_BASE                                             \
-       (test_thread_flag(TIF_32BIT_ADDR) ?                             \
-               PAGE_ALIGN(TASK_SIZE32 / 3) : PAGE_ALIGN(TASK_SIZE / 3))
 #define TASK_SIZE_OF(tsk)                                              \
-       (test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE)
+       (test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
 
 #define TASK_IS_32BIT_ADDR test_thread_flag(TIF_32BIT_ADDR)
 
 #endif
 
-#ifdef __KERNEL__
-#define STACK_TOP_MAX  TASK_SIZE
-#endif
+#define STACK_TOP      ((TASK_SIZE & PAGE_MASK) - SPECIAL_PAGES_SIZE)
+
+/*
+ * This decides where the kernel will search for a free chunk of vm
+ * space during mmap's.
+ */
+#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE / 3)
+
 
 #define NUM_FPU_REGS   32
 
diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index c2d53c1..8f7b5fd 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -35,7 +35,8 @@
 
 #ifdef CONFIG_64BIT
 
-#define __UA_LIMIT     (- TASK_SIZE)
+#define __UA_LIMIT     \
+       (test_thread_flag(TIF_32BIT_ADDR) ? 0xffffffff80000000ul : -TASK_SIZE64)
 
 #define __UA_ADDR      ".dword"
 #define __UA_LA                "dla"
-- 
1.7.2.3