Commit d19f5e41 authored by Helge Deller's avatar Helge Deller
Browse files

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: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
parent 554bfece

arch/parisc/include/asm/uaccess.h

+34 −25
Original line number Diff line number Diff line
@@ -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) */

arch/parisc/kernel/parisc_ksyms.c

+0 −10
Original line number Diff line number Diff line
@@ -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 $global$;

arch/parisc/lib/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

arch/parisc/lib/fixup.S

deleted100644 → 0
+0 −98
Original line number Diff line number Diff line 
/*

 * 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)

arch/parisc/mm/fault.c

+17 −0
Original line number Diff line number Diff line
@@ -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;

		/*

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