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Peter Anvin" , Theodore Ts'o , "Jason A. Donenfeld" , Arnd Bergmann , Andrew Morton , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Vincenzo Frascino , Shuah Khan , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom Message-ID: <20240827180819.GB2049@sol.localdomain> References: <5deb67090b214f0e6eae96b7c406546d1a16f89b.1724309198.git.christophe.leroy@csgroup.eu> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5deb67090b214f0e6eae96b7c406546d1a16f89b.1724309198.git.christophe.leroy@csgroup.eu> On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote: > With the current implementation, __cvdso_getrandom_data() calls > memset(), which is unexpected in the VDSO. > > Rewrite opaque data initialisation to avoid memset(). > > Signed-off-by: Christophe Leroy > --- > lib/vdso/getrandom.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > > diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c > index cab153c5f9be..4a56f45141b4 100644 > --- a/lib/vdso/getrandom.c > +++ b/lib/vdso/getrandom.c > @@ -4,6 +4,7 @@ > */ > > #include > +#include > #include > #include > #include > @@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_ > u32 counter[2] = { 0 }; > > if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) { > - *(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) { > - .size_of_opaque_state = sizeof(*state), > - .mmap_prot = PROT_READ | PROT_WRITE, > - .mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS > - }; > + struct vgetrandom_opaque_params *params = opaque_state; > + int i; > + > + params->size_of_opaque_state = sizeof(*state); > + params->mmap_prot = PROT_READ | PROT_WRITE; > + params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS; > + for (i = 0; i < ARRAY_SIZE(params->reserved); i++) > + params->reserved[i] = 0; > + > return 0; > } Is there a compiler flag that could be used to disable the generation of calls to memset? - Eric