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bpf: dispatcher: Allocate bpf_dispatcher->rw_image with vzalloc()

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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 vzalloc() to avoid permissions dance when
EXECMEM_BPF will be backed by ROX caches.

Using vzalloc() rather than vmalloc() ensures that the memory that
bpf_dispatcher_update() unconditionally copies into the executable buffer
is zeroed, which is not ideal but still better than random memory returned
by the existing bpf_jit_alloc_exec() or plain vmalloc().

Switching from bpf_jit_alloc_exec() to vzalloc() also saves a bit of
space in the more scarce module address space.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/bpf/20260716-execmem-x86-rox-bpf-v0-v3-1-4e76158c01c5@kernel.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Mike Rapoport (Microsoft)
2026-07-16 10:51:35 +03:00
committed by Kumar Kartikeya Dwivedi
parent a23a718233
commit 810a273919
1 changed files with 4 additions and 1 deletions
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5
kernel/bpf/dispatcher.c
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@@ -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, false);
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 vzalloc.
*/
d->rw_image = vzalloc(PAGE_SIZE);
if (!d->rw_image) {
bpf_prog_pack_free(d->image, PAGE_SIZE);
d->image = NULL;