Re: [PATCH v3 2/2] s390x: Use strpadcpy for copying vm name

[Thomas Huth <thuth@redhat.com>]

On 14/01/2021 08.07, Miroslav Rezanina wrote:
> Using strncpy with length equal to the size of target array, GCC 11
> reports following warning:
> 
>    warning: '__builtin_strncpy' specified bound 256 equals destination size [-Wstringop-truncation]
> 
> We can prevent this warning by using strpadcpy that copies string
> up to specified length, zeroes target array after copied string
> and does not raise warning when length is equal to target array
> size (and ending '\0' is discarded).
> 
> Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
> ---
>   target/s390x/kvm.c         | 12 +++++-------
>   target/s390x/misc_helper.c |  7 +++++--
>   2 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index b8385e6b95..dc27fa36c9 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -29,6 +29,7 @@
>   #include "internal.h"
>   #include "kvm_s390x.h"
>   #include "sysemu/kvm_int.h"
> +#include "qemu/cutils.h"
>   #include "qapi/error.h"
>   #include "qemu/error-report.h"
>   #include "qemu/timer.h"
> @@ -1910,18 +1911,15 @@ static void insert_stsi_3_2_2(S390CPU *cpu, __u64 addr, uint8_t ar)
>                                                       strlen(qemu_name)));
>       }
>       sysib.vm[0].ext_name_encoding = 2; /* 2 = UTF-8 */
> -    memset(sysib.ext_names[0], 0, sizeof(sysib.ext_names[0]));
>       /* If hypervisor specifies zero Extended Name in STSI322 SYSIB, it's
>        * considered by s390 as not capable of providing any Extended Name.
>        * Therefore if no name was specified on qemu invocation, we go with the
>        * same "KVMguest" default, which KVM has filled into short name field.
>        */
> -    if (qemu_name) {
> -        strncpy((char *)sysib.ext_names[0], qemu_name,
> -                sizeof(sysib.ext_names[0]));
> -    } else {
> -        strcpy((char *)sysib.ext_names[0], "KVMguest");
> -    }
> +    strpadcpy((char *)sysib.ext_names[0],
> +              sizeof(sysib.ext_names[0]),
> +              qemu_name ?: "KVMguest", '\0');
> +
>       /* Insert UUID */
>       memcpy(sysib.vm[0].uuid, &qemu_uuid, sizeof(sysib.vm[0].uuid));
>   
> diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
> index 58dbc023eb..7ea90d414a 100644
> --- a/target/s390x/misc_helper.c
> +++ b/target/s390x/misc_helper.c
> @@ -19,6 +19,7 @@
>    */
>   
>   #include "qemu/osdep.h"
> +#include "qemu/cutils.h"
>   #include "qemu/main-loop.h"
>   #include "cpu.h"
>   #include "internal.h"
> @@ -369,8 +370,10 @@ uint32_t HELPER(stsi)(CPUS390XState *env, uint64_t a0, uint64_t r0, uint64_t r1)
>                   ebcdic_put(sysib.sysib_322.vm[0].name, qemu_name,
>                              MIN(sizeof(sysib.sysib_322.vm[0].name),
>                                  strlen(qemu_name)));
> -                strncpy((char *)sysib.sysib_322.ext_names[0], qemu_name,
> -                        sizeof(sysib.sysib_322.ext_names[0]));
> +                strpadcpy((char *)sysib.sysib_322.ext_names[0],
> +                          sizeof(sysib.sysib_322.ext_names[0]),
> +                          qemu_name, '\0');
> +
>               } else {
>                   ebcdic_put(sysib.sysib_322.vm[0].name, "TCGguest", 8);
>                   strcpy((char *)sysib.sysib_322.ext_names[0], "TCGguest");
> 

Reviewed-by: Thomas Huth <thuth@redhat.com>