On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
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 christophe.leroy@csgroup.eu
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 <linux/minmax.h> +#include <linux/array_size.h> #include <vdso/datapage.h> #include <vdso/getrandom.h> #include <vdso/unaligned.h> @@ -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?
-fno-tree-loop-distribute-patterns . But, as always, read up on it, see what it actually does (and how it avoids your problem, and mostly: learn what the actual problem *was*!)
This might help with various loops, but it doesn't help with the matter that this patch fixes, which is struct initialization. I just tried it with the arm64 patch to no avail.