random: vDSO: avoid call to out of line memset()

With the current implementation, __cvdso_getrandom_data() calls
memset() on certain architectures, which is unexpected in the VDSO.

Rather than providing a memset(), simply rewrite opaque data
initialization to avoid memset().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index bacf19dbb6a11f37ca781098bddf251a66be25e1..1281fa3546c20fd16982da78fa6a4921f6c514ac 100644 (file)
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2022-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  */
 
+#include <linux/array_size.h>
 #include <linux/cache.h>
 #include <linux/kernel.h>
 #include <linux/time64.h>
@@ -73,11 +74,12 @@ __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;
+               params->size_of_opaque_state = sizeof(*state);
+               params->mmap_prot = PROT_READ | PROT_WRITE;
+               params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
+               for (size_t i = 0; i < ARRAY_SIZE(params->reserved); ++i)
+                       params->reserved[i] = 0;
                return 0;
        }