parisc: Clean up fixup routines for get_user()/put_user()

Al Viro noticed that userspace accesses via get_user()/put_user() can be
simplified a lot with regard to usage of the exception handling.

This patch implements a fixup routine for get_user() and put_user() in such
that the exception handler will automatically load -EFAULT into the register
%r8 (the error value) in case on a fault on userspace.  Additionally the fixup
routine will zero the target register on fault in case of a get_user() call.
The target register is extracted out of the faulting assembly instruction.

This patch brings a few benefits over the old implementation:
1. Exception handling gets much cleaner, easier and smaller in size.
2. Helper functions like fixup_get_user_skip_1 (all of fixup.S) can be dropped.
3. No need to hardcode %r9 as target register for get_user() any longer. This
   helps the compiler register allocator and thus creates less assembler
   statements.
4. No dependency on the exception_data contents any longer.
5. Nested faults will be handled cleanly.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index edfbf9d6a6dd76adae077d49d76a236d299bceda..8442727f28d2732eecb583d46bdcc88258a590dd 100644 (file)
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -64,6 +64,15 @@ struct exception_table_entry {
        ".word (" #fault_addr " - .), (" #except_addr " - .)\n\t" \
        ".previous\n"
 
+/*
+ * ASM_EXCEPTIONTABLE_ENTRY_EFAULT() creates a special exception table entry
+ * (with lowest bit set) for which the fault handler in fixup_exception() will
+ * load -EFAULT into %r8 for a read or write fault, and zeroes the target
+ * register in case of a read fault in get_user().
+ */
+#define ASM_EXCEPTIONTABLE_ENTRY_EFAULT( fault_addr, except_addr )\
+       ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr + 1)
+
 /*
  * The page fault handler stores, in a per-cpu area, the following information
  * if a fixup routine is available.
@@ -91,7 +100,7 @@ struct exception_data {
 #define __get_user(x, ptr)                               \
 ({                                                       \
        register long __gu_err __asm__ ("r8") = 0;       \
-       register long __gu_val __asm__ ("r9") = 0;       \
+       register long __gu_val;                          \
                                                         \
        load_sr2();                                      \
        switch (sizeof(*(ptr))) {                        \
@@ -107,22 +116,23 @@ struct exception_data {
 })
 
 #define __get_user_asm(ldx, ptr)                        \
-       __asm__("\n1:\t" ldx "\t0(%%sr2,%2),%0\n\t"     \
-               ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_get_user_skip_1)\
+       __asm__("1: " ldx " 0(%%sr2,%2),%0\n"           \
+               "9:\n"                                  \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
                : "=r"(__gu_val), "=r"(__gu_err)        \
-               : "r"(ptr), "1"(__gu_err)               \
-               : "r1");
+               : "r"(ptr), "1"(__gu_err));
 
 #if !defined(CONFIG_64BIT)
 
 #define __get_user_asm64(ptr)                          \
-       __asm__("\n1:\tldw 0(%%sr2,%2),%0"              \
-               "\n2:\tldw 4(%%sr2,%2),%R0\n\t"         \
-               ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_get_user_skip_2)\
-               ASM_EXCEPTIONTABLE_ENTRY(2b, fixup_get_user_skip_1)\
+       __asm__("   copy %%r0,%R0\n"                    \
+               "1: ldw 0(%%sr2,%2),%0\n"               \
+               "2: ldw 4(%%sr2,%2),%R0\n"              \
+               "9:\n"                                  \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b) \
                : "=r"(__gu_val), "=r"(__gu_err)        \
-               : "r"(ptr), "1"(__gu_err)               \
-               : "r1");
+               : "r"(ptr), "1"(__gu_err));
 
 #endif /* !defined(CONFIG_64BIT) */
 
@@ -148,32 +158,31 @@ struct exception_data {
  * The "__put_user/kernel_asm()" macros tell gcc they read from memory
  * instead of writing. This is because they do not write to any memory
  * gcc knows about, so there are no aliasing issues. These macros must
- * also be aware that "fixup_put_user_skip_[12]" are executed in the
- * context of the fault, and any registers used there must be listed
- * as clobbers. In this case only "r1" is used by the current routines.
- * r8/r9 are already listed as err/val.
+ * also be aware that fixups are executed in the context of the fault,
+ * and any registers used there must be listed as clobbers.
+ * r8 is already listed as err.
  */
 
 #define __put_user_asm(stx, x, ptr)                         \
        __asm__ __volatile__ (                              \
-               "\n1:\t" stx "\t%2,0(%%sr2,%1)\n\t"         \
-               ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_put_user_skip_1)\
+               "1: " stx " %2,0(%%sr2,%1)\n"               \
+               "9:\n"                                      \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)     \
                : "=r"(__pu_err)                            \
-               : "r"(ptr), "r"(x), "0"(__pu_err)           \
-               : "r1")
+               : "r"(ptr), "r"(x), "0"(__pu_err))
 
 
 #if !defined(CONFIG_64BIT)
 
 #define __put_user_asm64(__val, ptr) do {                  \
        __asm__ __volatile__ (                              \
-               "\n1:\tstw %2,0(%%sr2,%1)"                  \
-               "\n2:\tstw %R2,4(%%sr2,%1)\n\t"             \
-               ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_put_user_skip_2)\
-               ASM_EXCEPTIONTABLE_ENTRY(2b, fixup_put_user_skip_1)\
+               "1: stw %2,0(%%sr2,%1)\n"                   \
+               "2: stw %R2,4(%%sr2,%1)\n"                  \
+               "9:\n"                                      \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)     \
+               ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b)     \
                : "=r"(__pu_err)                            \
-               : "r"(ptr), "r"(__val), "0"(__pu_err) \
-               : "r1");                                    \
+               : "r"(ptr), "r"(__val), "0"(__pu_err));     \
 } while (0)
 
 #endif /* !defined(CONFIG_64BIT) */

diff --git a/arch/parisc/kernel/parisc_ksyms.c b/arch/parisc/kernel/parisc_ksyms.c
index 7484b3d11e0dbf83e58de4b64b08079b4a346bd7..c6d6272a934f03823b655cf07b38e7bbc01ca12e 100644 (file)
--- a/arch/parisc/kernel/parisc_ksyms.c
+++ b/arch/parisc/kernel/parisc_ksyms.c
@@ -47,16 +47,6 @@ EXPORT_SYMBOL(__cmpxchg_u64);
 EXPORT_SYMBOL(lclear_user);
 EXPORT_SYMBOL(lstrnlen_user);
 
-/* Global fixups - defined as int to avoid creation of function pointers */
-extern int fixup_get_user_skip_1;
-extern int fixup_get_user_skip_2;
-extern int fixup_put_user_skip_1;
-extern int fixup_put_user_skip_2;
-EXPORT_SYMBOL(fixup_get_user_skip_1);
-EXPORT_SYMBOL(fixup_get_user_skip_2);
-EXPORT_SYMBOL(fixup_put_user_skip_1);
-EXPORT_SYMBOL(fixup_put_user_skip_2);
-
 #ifndef CONFIG_64BIT
 /* Needed so insmod can set dp value */
 extern int $global$;

diff --git a/arch/parisc/lib/Makefile b/arch/parisc/lib/Makefile
index 8fa92b8d839abb98efb59bb4ac7689a40aeaf602..f2dac4d73b1b309cb2fbc28b744f948be8a35d11 100644 (file)
--- a/arch/parisc/lib/Makefile
+++ b/arch/parisc/lib/Makefile
@@ -2,7 +2,7 @@
 # Makefile for parisc-specific library files
 #
 
-lib-y  := lusercopy.o bitops.o checksum.o io.o memset.o fixup.o memcpy.o \
+lib-y  := lusercopy.o bitops.o checksum.o io.o memset.o memcpy.o \
           ucmpdi2.o delay.o
 
 obj-y  := iomap.o

diff --git a/arch/parisc/lib/fixup.S b/arch/parisc/lib/fixup.S
deleted file mode 100644 (file)
index a5b72f2..0000000
--- a/arch/parisc/lib/fixup.S
+++ /dev/null
@@ -1,98 +0,0 @@
-/*
- * Linux/PA-RISC Project (http://www.parisc-linux.org/)
- *
- *  Copyright (C) 2004  Randolph Chung <tausq@debian.org>
- *
- *    This program is free software; you can redistribute it and/or modify
- *    it under the terms of the GNU General Public License as published by
- *    the Free Software Foundation; either version 2, or (at your option)
- *    any later version.
- *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU General Public License for more details.
- *
- *    You should have received a copy of the GNU General Public License
- *    along with this program; if not, write to the Free Software
- *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- * 
- * Fixup routines for kernel exception handling.
- */
-#include <asm/asm-offsets.h>
-#include <asm/assembly.h>
-#include <asm/errno.h>
-#include <linux/linkage.h>
-
-#ifdef CONFIG_SMP
-       .macro  get_fault_ip t1 t2
-       loadgp
-       addil LT%__per_cpu_offset,%r27
-       LDREG RT%__per_cpu_offset(%r1),\t1
-       /* t2 = smp_processor_id() */
-       mfctl 30,\t2
-       ldw TI_CPU(\t2),\t2
-#ifdef CONFIG_64BIT
-       extrd,u \t2,63,32,\t2
-#endif
-       /* t2 = &__per_cpu_offset[smp_processor_id()]; */
-       LDREGX \t2(\t1),\t2 
-       addil LT%exception_data,%r27
-       LDREG RT%exception_data(%r1),\t1
-       /* t1 = this_cpu_ptr(&exception_data) */
-       add,l \t1,\t2,\t1
-       /* %r27 = t1->fault_gp - restore gp */
-       LDREG EXCDATA_GP(\t1), %r27
-       /* t1 = t1->fault_ip */
-       LDREG EXCDATA_IP(\t1), \t1
-       .endm
-#else
-       .macro  get_fault_ip t1 t2
-       loadgp
-       /* t1 = this_cpu_ptr(&exception_data) */
-       addil LT%exception_data,%r27
-       LDREG RT%exception_data(%r1),\t2
-       /* %r27 = t2->fault_gp - restore gp */
-       LDREG EXCDATA_GP(\t2), %r27
-       /* t1 = t2->fault_ip */
-       LDREG EXCDATA_IP(\t2), \t1
-       .endm
-#endif
-
-       .level LEVEL
-
-       .text
-       .section .fixup, "ax"
-
-       /* get_user() fixups, store -EFAULT in r8, and 0 in r9 */
-ENTRY_CFI(fixup_get_user_skip_1)
-       get_fault_ip %r1,%r8
-       ldo 4(%r1), %r1
-       ldi -EFAULT, %r8
-       bv %r0(%r1)
-       copy %r0, %r9
-ENDPROC_CFI(fixup_get_user_skip_1)
-
-ENTRY_CFI(fixup_get_user_skip_2)
-       get_fault_ip %r1,%r8
-       ldo 8(%r1), %r1
-       ldi -EFAULT, %r8
-       bv %r0(%r1)
-       copy %r0, %r9
-ENDPROC_CFI(fixup_get_user_skip_2)
-
-       /* put_user() fixups, store -EFAULT in r8 */
-ENTRY_CFI(fixup_put_user_skip_1)
-       get_fault_ip %r1,%r8
-       ldo 4(%r1), %r1
-       bv %r0(%r1)
-       ldi -EFAULT, %r8
-ENDPROC_CFI(fixup_put_user_skip_1)
-
-ENTRY_CFI(fixup_put_user_skip_2)
-       get_fault_ip %r1,%r8
-       ldo 8(%r1), %r1
-       bv %r0(%r1)
-       ldi -EFAULT, %r8
-ENDPROC_CFI(fixup_put_user_skip_2)
-

diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index deab89a8915a108a3fd98bef581605b59c094ab8..32ec22146141e56f9436bfbdfaccf0256820a552 100644 (file)
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -150,6 +150,23 @@ int fixup_exception(struct pt_regs *regs)
                d->fault_space = regs->isr;
                d->fault_addr = regs->ior;
 
+               /*
+                * Fix up get_user() and put_user().
+                * ASM_EXCEPTIONTABLE_ENTRY_EFAULT() sets the least-significant
+                * bit in the relative address of the fixup routine to indicate
+                * that %r8 should be loaded with -EFAULT to report a userspace
+                * access error.
+                */
+               if (fix->fixup & 1) {
+                       regs->gr[8] = -EFAULT;
+
+                       /* zero target register for get_user() */
+                       if (parisc_acctyp(0, regs->iir) == VM_READ) {
+                               int treg = regs->iir & 0x1f;
+                               regs->gr[treg] = 0;
+                       }
+               }
+
                regs->iaoq[0] = (unsigned long)&fix->fixup + fix->fixup;
                regs->iaoq[0] &= ~3;
                /*