[PATCH 6.1 186/197] parisc: Fix random data corruption from exception handler

Greg Kroah-Hartman
2024-02-20T21:07:41Z

From: Helge Deller <deller@gmx.de>

commit 8b1d72395635af45410b66cc4c4ab37a12c4a831 upstream.

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+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

---
arch/parisc/Kconfig | 1
arch/parisc/include/asm/assembly.h | 1
arch/parisc/include/asm/extable.h | 64 ++++++++++++++++++++++++++++++++
arch/parisc/include/asm/special_insns.h | 6 ++-
arch/parisc/include/asm/uaccess.h | 48 +++---------------------
arch/parisc/kernel/unaligned.c | 44 +++++++++++-----------
arch/parisc/mm/fault.c | 11 ++++-
7 files changed, 106 insertions(+), 69 deletions(-)

--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -24,7 +24,6 @@ config PARISC
select RTC_DRV_GENERIC
select INIT_ALL_POSSIBLE
select BUG
- select BUILDTIME_TABLE_SORT
select HAVE_PCI
select HAVE_PERF_EVENTS
select HAVE_KERNEL_BZIP2
--- a/arch/parisc/include/asm/assembly.h
+++ b/arch/parisc/include/asm/assembly.h
@@ -576,6 +576,7 @@
.section __ex_table,"aw" ! \
.align 4 ! \
.word (fault_addr - .), (except_addr - .) ! \
+ or %r0,%r0,%r0 ! \
.previous

--- /dev/null
+++ b/arch/parisc/include/asm/extable.h
@@ -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
--- a/arch/parisc/include/asm/special_insns.h
+++ b/arch/parisc/include/asm/special_insns.h
@@ -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" \
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -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
#define INLINE_COPY_TO_USER
#define INLINE_COPY_FROM_USER

-struct pt_regs;
-int fixup_exception(struct pt_regs *regs);
-
#endif /* __PARISC_UACCESS_H */
--- a/arch/parisc/kernel/unaligned.c
+++ b/arch/parisc/kernel/unaligned.c
@@ -118,8 +118,8 @@ static int emulate_ldh(struct pt_regs *r
"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) );

@@ -150,8 +150,8 @@ static int emulate_ldw(struct pt_regs *r
" 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) );

@@ -187,8 +187,8 @@ static int emulate_ldd(struct pt_regs *r
" 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" );
@@ -207,9 +207,9 @@ static int emulate_ldd(struct pt_regs *r
" 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) );
}
@@ -242,8 +242,8 @@ static int emulate_sth(struct pt_regs *r
"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) );

@@ -283,8 +283,8 @@ static int emulate_stw(struct pt_regs *r
" 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" );
@@ -327,10 +327,10 @@ static int emulate_std(struct pt_regs *r
"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" );
@@ -356,11 +356,11 @@ static int emulate_std(struct pt_regs *r
"4: stw %%r1,4(%%sr1,%3)\n"
"5: stw %2,8(%%sr1,%3)\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" (valh), "r" (vall), "r" (regs->ior), "r" (regs->isr)
: "r19", "r20", "r21", "r1" );
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -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) {