[PATCH 4.4 136/146] s390: fix test_fp_ctl inline assembly contraints

Greg Kroah-Hartman
2016-07-25T21:23:08Z

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

commit bcf4dd5f9ee096bd1510f838dd4750c35df4e38b upstream.

The test_fp_ctl function is used to test if a given value is a valid
floating-point control. The inline assembly in test_fp_ctl uses an
incorrect constraint for the 'orig_fpc' variable. If the compiler
chooses the same register for 'fpc' and 'orig_fpc' the test_fp_ctl()
function always returns true. This allows user space to trigger
kernel oopses with invalid floating-point control values on the
signal stack.

This problem has been introduced with git commit 4725c86055f5bbdcdf
"s390: fix save and restore of the floating-point-control register"

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/include/asm/fpu/api.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/include/asm/fpu/api.h
+++ b/arch/s390/include/asm/fpu/api.h
@@ -22,7 +22,7 @@ static inline int test_fp_ctl(u32 fpc)
" la %0,0\n"
"1:\n"
EX_TABLE(0b,1b)
- : "=d" (rc), "=d" (orig_fpc)
+ : "=d" (rc), "=&d" (orig_fpc)
: "d" (fpc), "0" (-EINVAL));
return rc;
}