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

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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>
This commit is contained in:
Helge Deller 2017-03-25 11:59:15 +01:00
parent 554bfeceb8
commit d19f5e41b3
5 changed files with 52 additions and 134 deletions
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59
arch/parisc/include/asm/uaccess.h
View File

@ -64,6 +64,15 @@ struct exception_table_entry {
".word (" #fault_addr " - .), (" #except_addr " - .)\n\t" \ ".word (" #fault_addr " - .), (" #except_addr " - .)\n\t" \
".previous\n" ".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 * The page fault handler stores, in a per-cpu area, the following information
* if a fixup routine is available. * if a fixup routine is available.
@ -91,7 +100,7 @@ struct exception_data {
#define __get_user(x, ptr) \ #define __get_user(x, ptr) \
({ \ ({ \
register long __gu_err __asm__ ("r8") = 0; \ register long __gu_err __asm__ ("r8") = 0; \
register long __gu_val __asm__ ("r9") = 0; \ register long __gu_val; \
\ \
load_sr2(); \ load_sr2(); \
switch (sizeof(*(ptr))) { \ switch (sizeof(*(ptr))) { \
@ -107,22 +116,23 @@ struct exception_data {
}) })
#define __get_user_asm(ldx, ptr) \ #define __get_user_asm(ldx, ptr) \
__asm__("\n1:\t" ldx "\t0(%%sr2,%2),%0\n\t" \ __asm__("1: " ldx " 0(%%sr2,%2),%0\n" \
ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_get_user_skip_1)\ "9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
: "=r"(__gu_val), "=r"(__gu_err) \ : "=r"(__gu_val), "=r"(__gu_err) \
: "r"(ptr), "1"(__gu_err) \ : "r"(ptr), "1"(__gu_err));
: "r1");
#if !defined(CONFIG_64BIT) #if !defined(CONFIG_64BIT)
#define __get_user_asm64(ptr) \ #define __get_user_asm64(ptr) \
__asm__("\n1:\tldw 0(%%sr2,%2),%0" \ __asm__(" copy %%r0,%R0\n" \
"\n2:\tldw 4(%%sr2,%2),%R0\n\t" \ "1: ldw 0(%%sr2,%2),%0\n" \
ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_get_user_skip_2)\ "2: ldw 4(%%sr2,%2),%R0\n" \
ASM_EXCEPTIONTABLE_ENTRY(2b, fixup_get_user_skip_1)\ "9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b) \
: "=r"(__gu_val), "=r"(__gu_err) \ : "=r"(__gu_val), "=r"(__gu_err) \
: "r"(ptr), "1"(__gu_err) \ : "r"(ptr), "1"(__gu_err));
: "r1");
#endif /* !defined(CONFIG_64BIT) */ #endif /* !defined(CONFIG_64BIT) */
@ -148,32 +158,31 @@ struct exception_data {
* The "__put_user/kernel_asm()" macros tell gcc they read from memory * 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 * 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 * 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 * also be aware that fixups are executed in the context of the fault,
* context of the fault, and any registers used there must be listed * and any registers used there must be listed as clobbers.
* as clobbers. In this case only "r1" is used by the current routines. * r8 is already listed as err.
* r8/r9 are already listed as err/val.
*/ */
#define __put_user_asm(stx, x, ptr) \ #define __put_user_asm(stx, x, ptr) \
__asm__ __volatile__ ( \ __asm__ __volatile__ ( \
"\n1:\t" stx "\t%2,0(%%sr2,%1)\n\t" \ "1: " stx " %2,0(%%sr2,%1)\n" \
ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_put_user_skip_1)\ "9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
: "=r"(__pu_err) \ : "=r"(__pu_err) \
: "r"(ptr), "r"(x), "0"(__pu_err) \ : "r"(ptr), "r"(x), "0"(__pu_err))
: "r1")
#if !defined(CONFIG_64BIT) #if !defined(CONFIG_64BIT)
#define __put_user_asm64(__val, ptr) do { \ #define __put_user_asm64(__val, ptr) do { \
__asm__ __volatile__ ( \ __asm__ __volatile__ ( \
"\n1:\tstw %2,0(%%sr2,%1)" \ "1: stw %2,0(%%sr2,%1)\n" \
"\n2:\tstw %R2,4(%%sr2,%1)\n\t" \ "2: stw %R2,4(%%sr2,%1)\n" \
ASM_EXCEPTIONTABLE_ENTRY(1b, fixup_put_user_skip_2)\ "9:\n" \
ASM_EXCEPTIONTABLE_ENTRY(2b, fixup_put_user_skip_1)\ ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b) \
: "=r"(__pu_err) \ : "=r"(__pu_err) \
: "r"(ptr), "r"(__val), "0"(__pu_err) \ : "r"(ptr), "r"(__val), "0"(__pu_err)); \
: "r1"); \
} while (0) } while (0)
#endif /* !defined(CONFIG_64BIT) */ #endif /* !defined(CONFIG_64BIT) */

10
arch/parisc/kernel/parisc_ksyms.c
View File

@ -47,16 +47,6 @@ EXPORT_SYMBOL(__cmpxchg_u64);
EXPORT_SYMBOL(lclear_user); EXPORT_SYMBOL(lclear_user);
EXPORT_SYMBOL(lstrnlen_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 #ifndef CONFIG_64BIT
/* Needed so insmod can set dp value */ /* Needed so insmod can set dp value */
extern int $global$; extern int $global$;

2
arch/parisc/lib/Makefile
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@ -2,7 +2,7 @@
# Makefile for parisc-specific library files # 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 ucmpdi2.o delay.o
obj-y := iomap.o obj-y := iomap.o

98
arch/parisc/lib/fixup.S
View File

@ -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)

17
arch/parisc/mm/fault.c
View File

@ -150,6 +150,23 @@ int fixup_exception(struct pt_regs *regs)
d->fault_space = regs->isr; d->fault_space = regs->isr;
d->fault_addr = regs->ior; 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] = (unsigned long)&fix->fixup + fix->fixup;
regs->iaoq[0] &= ~3; regs->iaoq[0] &= ~3;
/* /*