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bpf: Build-time assert that cpumask offset is zero

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The first element of a struct bpf_cpumask is a cpumask_t. This is done
to allow struct bpf_cpumask to be cast to a struct cpumask. If this
element were ever moved to another field, any BPF program passing a
struct bpf_cpumask * to a kfunc expecting a const struct cpumask * would
immediately fail to load. Add a build-time assertion so this is
assumption is captured and verified.

Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230128141537.100777-1-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
David Vernet 2023-01-28 08:15:37 -06:00 committed by Alexei Starovoitov
parent 70eb3911d8
commit cb4a21ea59
1 changed files with 3 additions and 0 deletions
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3
kernel/bpf/cpumask.c
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@ -52,6 +52,9 @@ struct bpf_cpumask *bpf_cpumask_create(void)
{
struct bpf_cpumask *cpumask;
/* cpumask must be the first element so struct bpf_cpumask be cast to struct cpumask. */
BUILD_BUG_ON(offsetof(struct bpf_cpumask, cpumask) != 0);
cpumask = bpf_mem_alloc(&bpf_cpumask_ma, sizeof(*cpumask));
if (!cpumask)
return NULL;