[PATCH v4 2/2] m68k: improve __constant_copy_to_user_asm() fault handling

Michael Schmitz
2024-04-29T03:09:54Z

A problem similar to that reported for __put_user_asm and
__generic_copy_to_user is also present in
__constant_copy_to_user_asm.

Address the problem by extending the exception table to cover
two instructions past each moves instruction, and adding a
single NOP at the very end to catch faults on the final
instruction (which is not guaranteed to be a movesb!).

Tested on 68030 (Atari Falcon 030) with a transfer beginning
at a single byte at the end of a mapped page followed by
seven more bytes on an unmapped page (testcase derived from
stress-ng sysbadaddr stressor by Finn Thain and modified to
use the llseek syscall).

Cc: Finn Thain <fthain@linux-m68k.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Finn Thain <fthain@linux-m68k.org>
Link: https://lore.kernel.org/all/e0f23460779e6d16e2633486ac4841790ef2aca0.1713176294.git.fthain@linux-m68k.org
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---
arch/m68k/include/asm/uaccess.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/m68k/include/asm/uaccess.h b/arch/m68k/include/asm/uaccess.h
index 44e52d8323e5..f1f4b62d6f69 100644
--- a/arch/m68k/include/asm/uaccess.h
+++ b/arch/m68k/include/asm/uaccess.h
@@ -288,10 +288,11 @@ __constant_copy_from_user(void *to, const void __user *from, unsigned long n)
"21: "MOVES"."#s2" %3,(%1)+\n" \
"22:\n" \
" .ifnc \""#s3"\",\"\"\n" \
- " move."#s3" (%2)+,%3\n" \
- "31: "MOVES"."#s3" %3,(%1)+\n" \
- "32:\n" \
+ "31: move."#s3" (%2)+,%3\n" \
+ "32: "MOVES"."#s3" %3,(%1)+\n" \
+ "33:\n" \
" .endif\n" \
+ "34: nop\n" \
"4:\n" \
"\n" \
" .section __ex_table,\"a\"\n" \
@@ -303,7 +304,9 @@ __constant_copy_from_user(void *to, const void __user *from, unsigned long n)
" .ifnc \""#s3"\",\"\"\n" \
" .long 31b,5f\n" \
" .long 32b,5f\n" \
+ " .long 33b,5f\n" \
" .endif\n" \
+ " .long 34b,5f\n" \
" .previous\n" \
"\n" \
" .section .fixup,\"ax\"\n" \
--
2.17.1