memfd: Avoid Coverity warning about integer overflow

[Qemu-devel] [PATCH] memfd: Avoid Coverity warning about integer overflow

Posted by Peter Maydell 5 years, 11 months ago

Coverity complains about qemu_memfd_create() (CID 1385858) because
we calculate a bit position htsize which could be up to 63, but
then use it in "1 << htsize" which is a 32-bit integer calculation
and could push the 1 off the top of the value.

Silence the complaint bu using "1ULL"; this isn't a bug in
practice since a hugetlbsize of 4GB is not very plausible.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 util/memfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/util/memfd.c b/util/memfd.c
index b3ecbac19e..d248a53c3c 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -66,7 +66,7 @@ int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
 {
     int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
 
-    if (htsize && 1 << htsize != hugetlbsize) {
+    if (htsize && 1ULL << htsize != hugetlbsize) {
         error_setg(errp, "Hugepage size must be a power of 2");
         return -1;
     }
-- 
2.17.0

Re: [Qemu-devel] [PATCH] memfd: Avoid Coverity warning about integer overflow

Posted by Marc-André Lureau 5 years, 11 months ago

On Tue, May 15, 2018 at 7:27 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> Coverity complains about qemu_memfd_create() (CID 1385858) because
> we calculate a bit position htsize which could be up to 63, but
> then use it in "1 << htsize" which is a 32-bit integer calculation
> and could push the 1 off the top of the value.
>
> Silence the complaint bu using "1ULL"; this isn't a bug in
> practice since a hugetlbsize of 4GB is not very plausible.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Thanks Peter for the fix,

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  util/memfd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/util/memfd.c b/util/memfd.c
> index b3ecbac19e..d248a53c3c 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -66,7 +66,7 @@ int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>  {
>      int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
>
> -    if (htsize && 1 << htsize != hugetlbsize) {
> +    if (htsize && 1ULL << htsize != hugetlbsize) {
>          error_setg(errp, "Hugepage size must be a power of 2");
>          return -1;
>      }
> --
> 2.17.0
>
>



-- 
Marc-André Lureau

Re: [Qemu-devel] [PATCH] memfd: Avoid Coverity warning about integer overflow

Posted by Alex Bennée 5 years, 11 months ago

Peter Maydell <peter.maydell@linaro.org> writes:

> Coverity complains about qemu_memfd_create() (CID 1385858) because
> we calculate a bit position htsize which could be up to 63, but
> then use it in "1 << htsize" which is a 32-bit integer calculation
> and could push the 1 off the top of the value.
>
> Silence the complaint bu using "1ULL"; this isn't a bug in
> practice since a hugetlbsize of 4GB is not very plausible.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  util/memfd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/util/memfd.c b/util/memfd.c
> index b3ecbac19e..d248a53c3c 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -66,7 +66,7 @@ int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>  {
>      int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
>
> -    if (htsize && 1 << htsize != hugetlbsize) {
> +    if (htsize && 1ULL << htsize != hugetlbsize) {
>          error_setg(errp, "Hugepage size must be a power of 2");
>          return -1;
>      }


--
Alex Bennée

Re: [Qemu-devel] [PATCH] memfd: Avoid Coverity warning about integer overflow

Posted by Paolo Bonzini 5 years, 11 months ago

On 15/05/2018 19:27, Peter Maydell wrote:
> Coverity complains about qemu_memfd_create() (CID 1385858) because
> we calculate a bit position htsize which could be up to 63, but
> then use it in "1 << htsize" which is a 32-bit integer calculation
> and could push the 1 off the top of the value.
> 
> Silence the complaint bu using "1ULL"; this isn't a bug in
> practice since a hugetlbsize of 4GB is not very plausible.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  util/memfd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/util/memfd.c b/util/memfd.c
> index b3ecbac19e..d248a53c3c 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -66,7 +66,7 @@ int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>  {
>      int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
>  
> -    if (htsize && 1 << htsize != hugetlbsize) {
> +    if (htsize && 1ULL << htsize != hugetlbsize) {
>          error_setg(errp, "Hugepage size must be a power of 2");
>          return -1;
>      }
> 

Queued, thanks.

Paolo