[PATCH bpf-next 1/5] bpf: dispatcher: allocate bpf_dispatcher->rw_image with vmalloc()

[Mike Rapoport (Microsoft)]

bpf_dispatcher->rw_image is a temporary writable buffer that
arch_prepare_bpf_dispatcher() fills and then copies into
bpf_dispatcher->image using bpf_arch_text_copy().

The rel32 offsets emitted by emit_bpf_dispatcher() are calculated against
->image, so ->rw_image does not need to live in the module address range.

Allocate ->rw_image with vmalloc() to avoid permissions dance when
EXECMEM_BPF will be backed by ROX caches.

Also saves a bit of space in the more scarce module address space.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 kernel/bpf/dispatcher.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
index b77db7413f8c..a7a6a375cdd3 100644
--- a/kernel/bpf/dispatcher.c
+++ b/kernel/bpf/dispatcher.c
@@ -148,7 +148,10 @@ void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
 		d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero);
 		if (!d->image)
 			goto out;
-		d->rw_image = bpf_jit_alloc_exec(PAGE_SIZE);
+		/* d->rw_image doesn't need to be in module memory range, so we
+		 * can use vmalloc.
+		 */
+		d->rw_image = vmalloc(PAGE_SIZE);
 		if (!d->rw_image) {
 			bpf_prog_pack_free(d->image, PAGE_SIZE);
 			d->image = NULL;

-- 
2.53.0