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parisc: Fix random data corruption from exception handler

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The current exception handler implementation, which assists when accessing
user space memory, may exhibit random data corruption if the compiler decides
to use a different register than the specified register %r29 (defined in
ASM_EXCEPTIONTABLE_REG) for the error code. If the compiler choose another
register, the fault handler will nevertheless store -EFAULT into %r29 and thus
trash whatever this register is used for.
Looking at the assembly I found that this happens sometimes in emulate_ldd().

To solve the issue, the easiest solution would be if it somehow is
possible to tell the fault handler which register is used to hold the error
code. Using %0 or %1 in the inline assembly is not posssible as it will show
up as e.g. %r29 (with the "%r" prefix), which the GNU assembler can not
convert to an integer.

This patch takes another, better and more flexible approach:
We extend the __ex_table (which is out of the execution path) by one 32-word.
In this word we tell the compiler to insert the assembler instruction
"or %r0,%r0,%reg", where %reg references the register which the compiler
choosed for the error return code.
In case of an access failure, the fault handler finds the __ex_table entry and
can examine the opcode. The used register is encoded in the lowest 5 bits, and
the fault handler can then store -EFAULT into this register.

Since we extend the __ex_table to 3 words we can't use the BUILDTIME_TABLE_SORT
config option any longer.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # v6.0+
This commit is contained in:
Helge Deller 2024-01-20 15:29:27 +01:00
parent 20e08a720c
commit 8b1d723956
8 changed files with 108 additions and 71 deletions
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1
arch/parisc/Kconfig
View File

@ -25,7 +25,6 @@ config PARISC
select RTC_DRV_GENERIC
select INIT_ALL_POSSIBLE
select BUG
select BUILDTIME_TABLE_SORT
select HAVE_KERNEL_UNCOMPRESSED
select HAVE_PCI
select HAVE_PERF_EVENTS

1
arch/parisc/include/asm/assembly.h
View File

@ -576,6 +576,7 @@
.section __ex_table,"aw" ! \
.align 4 ! \
.word (fault_addr - .), (except_addr - .) ! \
or %r0,%r0,%r0 ! \
.previous

64
arch/parisc/include/asm/extable.h Normal file
View File

@ -0,0 +1,64 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __PARISC_EXTABLE_H
#define __PARISC_EXTABLE_H
#include <asm/ptrace.h>
#include <linux/compiler.h>
/*
* The exception table consists of three addresses:
*
* - A relative address to the instruction that is allowed to fault.
* - A relative address at which the program should continue (fixup routine)
* - An asm statement which specifies which CPU register will
* receive -EFAULT when an exception happens if the lowest bit in
* the fixup address is set.
*
* Note: The register specified in the err_opcode instruction will be
* modified at runtime if a fault happens. Register %r0 will be ignored.
*
* Since relative addresses are used, 32bit values are sufficient even on
* 64bit kernel.
*/
struct pt_regs;
int fixup_exception(struct pt_regs *regs);
#define ARCH_HAS_RELATIVE_EXTABLE
struct exception_table_entry {
int insn; /* relative address of insn that is allowed to fault. */
int fixup; /* relative address of fixup routine */
int err_opcode; /* sample opcode with register which holds error code */
};
#define ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr, opcode )\
".section __ex_table,\"aw\"\n" \
".align 4\n" \
".word (" #fault_addr " - .), (" #except_addr " - .)\n" \
opcode "\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 on fault into the register specified by the err_opcode instruction,
* and zeroes the target register in case of a read fault in get_user().
*/
#define ASM_EXCEPTIONTABLE_VAR(__err_var) \
int __err_var = 0
#define ASM_EXCEPTIONTABLE_ENTRY_EFAULT( fault_addr, except_addr, register )\
ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr + 1, "or %%r0,%%r0," register)
static inline void swap_ex_entry_fixup(struct exception_table_entry *a,
struct exception_table_entry *b,
struct exception_table_entry tmp,
int delta)
{
a->fixup = b->fixup + delta;
b->fixup = tmp.fixup - delta;
a->err_opcode = b->err_opcode;
b->err_opcode = tmp.err_opcode;
}
#define swap_ex_entry_fixup swap_ex_entry_fixup
#endif

6
arch/parisc/include/asm/special_insns.h
View File

@ -8,7 +8,8 @@
"copy %%r0,%0\n" \
"8:\tlpa %%r0(%1),%0\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY(8b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY(8b, 9b, \
"or %%r0,%%r0,%%r0") \
: "=&r" (pa) \
: "r" (va) \
: "memory" \
@ -22,7 +23,8 @@
"copy %%r0,%0\n" \
"8:\tlpa %%r0(%%sr3,%1),%0\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY(8b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY(8b, 9b, \
"or %%r0,%%r0,%%r0") \
: "=&r" (pa) \
: "r" (va) \
: "memory" \

48
arch/parisc/include/asm/uaccess.h
View File

@ -7,6 +7,7 @@
*/
#include <asm/page.h>
#include <asm/cache.h>
#include <asm/extable.h>
#include <linux/bug.h>
#include <linux/string.h>
@ -26,37 +27,6 @@
#define STD_USER(sr, x, ptr) __put_user_asm(sr, "std", x, ptr)
#endif
/*
* The exception table contains two values: the first is the relative offset to
* the address of the instruction that is allowed to fault, and the second is
* the relative offset to the address of the fixup routine. Since relative
* addresses are used, 32bit values are sufficient even on 64bit kernel.
*/
#define ARCH_HAS_RELATIVE_EXTABLE
struct exception_table_entry {
int insn; /* relative address of insn that is allowed to fault. */
int fixup; /* relative address of fixup routine */
};
#define ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr )\
".section __ex_table,\"aw\"\n" \
".align 4\n" \
".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 %r29 for a read or write fault, and zeroes the target
* register in case of a read fault in get_user().
*/
#define ASM_EXCEPTIONTABLE_REG 29
#define ASM_EXCEPTIONTABLE_VAR(__variable) \
register long __variable __asm__ ("r29") = 0
#define ASM_EXCEPTIONTABLE_ENTRY_EFAULT( fault_addr, except_addr )\
ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr + 1)
#define __get_user_internal(sr, val, ptr) \
({ \
ASM_EXCEPTIONTABLE_VAR(__gu_err); \
@ -83,7 +53,7 @@ struct exception_table_entry {
\
__asm__("1: " ldx " 0(%%sr%2,%3),%0\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b, "%1") \
: "=r"(__gu_val), "+r"(__gu_err) \
: "i"(sr), "r"(ptr)); \
\
@ -115,8 +85,8 @@ struct exception_table_entry {
"1: ldw 0(%%sr%2,%3),%0\n" \
"2: ldw 4(%%sr%2,%3),%R0\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b, "%1") \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b, "%1") \
: "=&r"(__gu_tmp.l), "+r"(__gu_err) \
: "i"(sr), "r"(ptr)); \
\
@ -174,7 +144,7 @@ struct exception_table_entry {
__asm__ __volatile__ ( \
"1: " stx " %1,0(%%sr%2,%3)\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b, "%0") \
: "+r"(__pu_err) \
: "r"(x), "i"(sr), "r"(ptr))
@ -186,15 +156,14 @@ struct exception_table_entry {
"1: stw %1,0(%%sr%2,%3)\n" \
"2: stw %R1,4(%%sr%2,%3)\n" \
"9:\n" \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b) \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b, "%0") \
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b, "%0") \
: "+r"(__pu_err) \
: "r"(__val), "i"(sr), "r"(ptr)); \
} while (0)
#endif /* !defined(CONFIG_64BIT) */
/*
* Complex access routines -- external declarations
*/
@ -216,7 +185,4 @@ unsigned long __must_check raw_copy_from_user(void *dst, const void __user *src,
#define INLINE_COPY_TO_USER
#define INLINE_COPY_FROM_USER
struct pt_regs;
int fixup_exception(struct pt_regs *regs);
#endif /* __PARISC_UACCESS_H */

4
arch/parisc/kernel/cache.c
View File

@ -854,7 +854,7 @@ SYSCALL_DEFINE3(cacheflush, unsigned long, addr, unsigned long, bytes,
#endif
" fic,m %3(%4,%0)\n"
"2: sync\n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 2b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 2b, "%1")
: "+r" (start), "+r" (error)
: "r" (end), "r" (dcache_stride), "i" (SR_USER));
}
@ -869,7 +869,7 @@ SYSCALL_DEFINE3(cacheflush, unsigned long, addr, unsigned long, bytes,
#endif
" fdc,m %3(%4,%0)\n"
"2: sync\n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 2b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 2b, "%1")
: "+r" (start), "+r" (error)
: "r" (end), "r" (icache_stride), "i" (SR_USER));
}

44
arch/parisc/kernel/unaligned.c
View File

@ -120,8 +120,8 @@ static int emulate_ldh(struct pt_regs *regs, int toreg)
"2: ldbs 1(%%sr1,%3), %0\n"
" depw %2, 23, 24, %0\n"
"3: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%1")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%1")
: "+r" (val), "+r" (ret), "=&r" (temp1)
: "r" (saddr), "r" (regs->isr) );
@ -152,8 +152,8 @@ static int emulate_ldw(struct pt_regs *regs, int toreg, int flop)
" mtctl %2,11\n"
" vshd %0,%3,%0\n"
"3: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%1")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%1")
: "+r" (val), "+r" (ret), "=&r" (temp1), "=&r" (temp2)
: "r" (saddr), "r" (regs->isr) );
@ -189,8 +189,8 @@ static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
" mtsar %%r19\n"
" shrpd %0,%%r20,%%sar,%0\n"
"3: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%1")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%1")
: "=r" (val), "+r" (ret)
: "0" (val), "r" (saddr), "r" (regs->isr)
: "r19", "r20" );
@ -209,9 +209,9 @@ static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
" vshd %0,%R0,%0\n"
" vshd %R0,%4,%R0\n"
"4: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 4b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 4b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 4b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 4b, "%1")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 4b, "%1")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 4b, "%1")
: "+r" (val), "+r" (ret), "+r" (saddr), "=&r" (shift), "=&r" (temp1)
: "r" (regs->isr) );
}
@ -244,8 +244,8 @@ static int emulate_sth(struct pt_regs *regs, int frreg)
"1: stb %1, 0(%%sr1, %3)\n"
"2: stb %2, 1(%%sr1, %3)\n"
"3: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%0")
: "+r" (ret), "=&r" (temp1)
: "r" (val), "r" (regs->ior), "r" (regs->isr) );
@ -285,8 +285,8 @@ static int emulate_stw(struct pt_regs *regs, int frreg, int flop)
" stw %%r20,0(%%sr1,%2)\n"
" stw %%r21,4(%%sr1,%2)\n"
"3: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%0")
: "+r" (ret)
: "r" (val), "r" (regs->ior), "r" (regs->isr)
: "r19", "r20", "r21", "r22", "r1" );
@ -329,10 +329,10 @@ static int emulate_std(struct pt_regs *regs, int frreg, int flop)
"3: std %%r20,0(%%sr1,%2)\n"
"4: std %%r21,8(%%sr1,%2)\n"
"5: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 5b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 5b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 5b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(4b, 5b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 5b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 5b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 5b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(4b, 5b, "%0")
: "+r" (ret)
: "r" (val), "r" (regs->ior), "r" (regs->isr)
: "r19", "r20", "r21", "r22", "r1" );
@ -357,11 +357,11 @@ static int emulate_std(struct pt_regs *regs, int frreg, int flop)
"4: stw %%r1,4(%%sr1,%2)\n"
"5: stw %R1,8(%%sr1,%2)\n"
"6: \n"
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 6b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 6b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 6b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(4b, 6b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(5b, 6b)
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 6b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 6b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 6b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(4b, 6b, "%0")
ASM_EXCEPTIONTABLE_ENTRY_EFAULT(5b, 6b, "%0")
: "+r" (ret)
: "r" (val), "r" (regs->ior), "r" (regs->isr)
: "r19", "r20", "r21", "r1" );

11
arch/parisc/mm/fault.c
View File

@ -150,11 +150,16 @@ int fixup_exception(struct pt_regs *regs)
* 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 gr[ASM_EXCEPTIONTABLE_REG] should be loaded with
* -EFAULT to report a userspace access error.
* that the register encoded in the "or %r0,%r0,register"
* opcode should be loaded with -EFAULT to report a userspace
* access error.
*/
if (fix->fixup & 1) {
regs->gr[ASM_EXCEPTIONTABLE_REG] = -EFAULT;
int fault_error_reg = fix->err_opcode & 0x1f;
if (!WARN_ON(!fault_error_reg))
regs->gr[fault_error_reg] = -EFAULT;
pr_debug("Unalignment fixup of register %d at %pS\n",
fault_error_reg, (void*)regs->iaoq[0]);
/* zero target register for get_user() */
if (parisc_acctyp(0, regs->iir) == VM_READ) {