uaccess: reimplement probe_kernel_address() using probe_kernel_read()

probe_kernel_address() is basically the same as the (later added)
probe_kernel_read().

The return value on EFAULT is a bit different: probe_kernel_address()
returns number-of-bytes-not-copied whereas probe_kernel_read() returns
-EFAULT.  All callers have been checked, none cared.

probe_kernel_read() can be overridden by the architecture whereas
probe_kernel_address() cannot.  parisc, blackfin and um do this, to insert
additional checking.  Hence this patch possibly fixes obscure bugs,
although there are only two probe_kernel_address() callsites outside
arch/.

My first attempt involved removing probe_kernel_address() entirely and
converting all callsites to use probe_kernel_read() directly, but that got
tiresome.

This patch shrinks mm/slab_common.o by 218 bytes.  For a single
probe_kernel_address() callsite.

Cc: Steven Miao <realmz6@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 17 insertions, 32 deletions

diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index 00b7f7de28a1..7d5f4c736a16 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -803,7 +803,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
                         }
                 }
         } else {
-                fault = probe_kernel_address(instrptr, instr);
+                fault = probe_kernel_address((void *)instrptr, instr);
                 instr = __mem_to_opcode_arm(instr);
         }
 
diff --git a/arch/powerpc/sysdev/fsl_pci.c b/arch/powerpc/sysdev/fsl_pci.c
index ebc1f412cf49..13b9bcf5485e 100644
--- a/arch/powerpc/sysdev/fsl_pci.c
+++ b/arch/powerpc/sysdev/fsl_pci.c
@@ -999,7 +999,7 @@ int fsl_pci_mcheck_exception(struct pt_regs *regs)
                         ret = get_user(regs->nip, &inst);
                         pagefault_enable();
                 } else {
-                        ret = probe_kernel_address(regs->nip, inst);
+                        ret = probe_kernel_address((void *)regs->nip, inst);
                 }
 
                 if (mcheck_handle_load(regs, inst)) {
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index d6f2c2c5b043..558129af828a 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -75,36 +75,6 @@ static inline unsigned long __copy_from_user_nocache(void *to,
 
 #endif          /* ARCH_HAS_NOCACHE_UACCESS */
 
-/**
- * probe_kernel_address(): safely attempt to read from a location
- * @addr: address to read from - its type is type typeof(retval)*
- * @retval: read into this variable
- *
- * Safely read from address @addr into variable @revtal.  If a kernel fault
- * happens, handle that and return -EFAULT.
- * We ensure that the __get_user() is executed in atomic context so that
- * do_page_fault() doesn't attempt to take mmap_sem.  This makes
- * probe_kernel_address() suitable for use within regions where the caller
- * already holds mmap_sem, or other locks which nest inside mmap_sem.
- * This must be a macro because __get_user() needs to know the types of the
- * args.
- *
- * We don't include enough header files to be able to do the set_fs().  We
- * require that the probe_kernel_address() caller will do that.
- */
-#define probe_kernel_address(addr, retval)              \
-        ({                                              \
-                long ret;                               \
-                mm_segment_t old_fs = get_fs();         \
-                                                        \
-                set_fs(KERNEL_DS);                      \
-                pagefault_disable();                    \
-                ret = __copy_from_user_inatomic(&(retval), (__force typeof(retval) __user *)(addr), sizeof(retval));            \
-                pagefault_enable();                     \
-                set_fs(old_fs);                         \
-                ret;                                    \
-        })
-
 /*
  * probe_kernel_read(): safely attempt to read from a location
  * @dst: pointer to the buffer that shall take the data
@@ -131,4 +101,14 @@ extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size
 
 extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
 
+/**
+ * probe_kernel_address(): safely attempt to read from a location
+ * @addr: address to read from
+ * @retval: read into this variable
+ *
+ * Returns 0 on success, or -EFAULT.
+ */
+#define probe_kernel_address(addr, retval)              \
+        probe_kernel_read(&retval, addr, sizeof(retval))
+
 #endif          /* __LINUX_UACCESS_H__ */
diff --git a/mm/maccess.c b/mm/maccess.c
index 34fe24759ed1..1b13638d238d 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -13,6 +13,11 @@
  *
  * Safely read from address @src to the buffer at @dst.  If a kernel fault
  * happens, handle that and return -EFAULT.
+ *
+ * We ensure that the copy_from_user is executed in atomic context so that
+ * do_page_fault() doesn't attempt to take mmap_sem.  This makes
+ * probe_kernel_read() suitable for use within regions where the caller
+ * already holds mmap_sem, or other locks which nest inside mmap_sem.
  */
 
 long __weak probe_kernel_read(void *dst, const void *src, size_t size)