s390/checksum: always use cksm instruction

Commit dfe843dce775 ("s390/checksum: support GENERIC_CSUM, enable it for
KASAN") switched s390 to use the generic checksum functions, so that KASAN
instrumentation also works checksum functions by avoiding architecture
specific inline assemblies.

There is however the problem that the generic csum_partial() function
returns a 32 bit value with a 16 bit folded checksum, while the original
s390 variant does not fold to 16 bit. This in turn causes that the
ipib_checksum in lowcore contains different values depending on kernel
config options.

The ipib_checksum is used by system dumpers to verify if pointers in
lowcore point to valid data. Verification is done by comparing checksum
values. The system dumpers still use 32 bit checksum values which are not
folded, and therefore the checksum verification fails (incorrectly).

Symptom is that reboot after dump does not work anymore when a KASAN
instrumented kernel is dumped.

Fix this by not using the generic checksum implementation. Instead add an
explicit kasan_check_read() so that KASAN knows about the read access from
within the inline assembly.

Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Fixes: dfe843dce775 ("s390/checksum: support GENERIC_CSUM, enable it for KASAN")
Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index d4db47b0610c3d72463748c99a4999548516033d..a7568449ca59c7a6525e9ebeee78a8be748029dc 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -26,10 +26,6 @@ config GENERIC_BUG
 config GENERIC_BUG_RELATIVE_POINTERS
        def_bool y
 
-config GENERIC_CSUM
-       bool
-       default y if KASAN
-
 config GENERIC_LOCKBREAK
        def_bool y if PREEMPTION
 

diff --git a/arch/s390/include/asm/checksum.h b/arch/s390/include/asm/checksum.h
index d977a3a2f6190cfecced8c8ea34531420f10bbfe..1b6b992cf18ed81dc4d3b27d3d437ac17dce966c 100644 (file)
--- a/arch/s390/include/asm/checksum.h
+++ b/arch/s390/include/asm/checksum.h
@@ -12,12 +12,7 @@
 #ifndef _S390_CHECKSUM_H
 #define _S390_CHECKSUM_H
 
-#ifdef CONFIG_GENERIC_CSUM
-
-#include <asm-generic/checksum.h>
-
-#else /* CONFIG_GENERIC_CSUM */
-
+#include <linux/kasan-checks.h>
 #include <linux/uaccess.h>
 #include <linux/in6.h>
 
@@ -40,6 +35,7 @@ static inline __wsum csum_partial(const void *buff, int len, __wsum sum)
                .odd = (unsigned long) len,
        };
 
+       kasan_check_read(buff, len);
        asm volatile(
                "0:     cksm    %[sum],%[rp]\n"
                "       jo      0b\n"
@@ -135,5 +131,4 @@ static inline __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
        return csum_fold((__force __wsum)(sum >> 32));
 }
 
-#endif /* CONFIG_GENERIC_CSUM */
 #endif /* _S390_CHECKSUM_H */