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References: <20180515172729.24564-1-peter.maydell@linaro.org>
From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
In-reply-to: <20180515172729.24564-1-peter.maydell@linaro.org>
Date: Tue, 15 May 2018 20:27:49 +0100
Message-ID: <87zi10en2i.fsf@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH] memfd: Avoid Coverity warning about
 integer overflow
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@redhat.com>, patches@linaro.org


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 Benn=C3=A9e <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, bo=
ol hugetlb,
>  {
>      int htsize =3D hugetlbsize ? ctz64(hugetlbsize) : 0;
>
> -    if (htsize && 1 << htsize !=3D hugetlbsize) {
> +    if (htsize && 1ULL << htsize !=3D hugetlbsize) {
>          error_setg(errp, "Hugepage size must be a power of 2");
>          return -1;
>      }


--
Alex Benn=C3=A9e