Re: [PATCH bpf-next v2 5/5] selftests/bpf: check if bpf_fastcall is recognized for kfuncs

[Yonghong Song <yonghong.song@linux.dev>]

On 8/16/24 6:51 PM, Eduard Zingerman wrote:
> Use kfunc_bpf_cast_to_kern_ctx() and kfunc_bpf_rdonly_cast() to verify
> that bpf_fastcall pattern is recognized for kfunc calls.
>
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

LGTM with a nit below.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

> ---
>   .../bpf/progs/verifier_bpf_fastcall.c         | 50 +++++++++++++++++++
>   1 file changed, 50 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c b/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
> index f75cd5e3fffe..97c2420ccb38 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_bpf_fastcall.c
> @@ -2,8 +2,11 @@
>   
>   #include <linux/bpf.h>
>   #include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_core_read.h>
>   #include "../../../include/linux/filter.h"
>   #include "bpf_misc.h"
> +#include <stdbool.h>
> +#include "bpf_kfuncs.h"
>   
>   SEC("raw_tp")
>   __arch_x86_64
> @@ -793,4 +796,51 @@ __naked int bpf_fastcall_max_stack_fail(void)
>   	);
>   }
>   
> +SEC("cgroup/getsockname_unix")
> +__xlated("0: r2 = 1")
> +/* bpf_cast_to_kern_ctx is replaced by a single assignment */
> +__xlated("1: r0 = r1")
> +__xlated("2: r0 = r2")
> +__xlated("3: exit")
> +__success
> +__naked void kfunc_bpf_cast_to_kern_ctx(void)
> +{
> +	asm volatile (
> +	"r2 = 1;"
> +	"*(u64 *)(r10 - 32) = r2;"
> +	"call %[bpf_cast_to_kern_ctx];"
> +	"r2 = *(u64 *)(r10 - 32);"
> +	"r0 = r2;"
> +	"exit;"
> +	:
> +	: __imm(bpf_cast_to_kern_ctx)
> +	: __clobber_all);
> +}
> +
> +SEC("raw_tp")
> +__xlated("3: r3 = 1")
> +/* bpf_rdonly_cast is replaced by a single assignment */
> +__xlated("4: r0 = r1")
> +__xlated("5: r0 = r3")
> +void kfunc_bpf_rdonly_cast(void)
> +{
> +	asm volatile (
> +	"r2 = %[btf_id];"
> +	"r3 = 1;"
> +	"*(u64 *)(r10 - 32) = r3;"
> +	"call %[bpf_rdonly_cast];"
> +	"r3 = *(u64 *)(r10 - 32);"
> +	"r0 = r3;"
> +	:
> +	: __imm(bpf_rdonly_cast),
> +	 [btf_id]"r"(bpf_core_type_id_kernel(union bpf_attr))
> +	: __clobber_common);
> +}
> +
> +void kfunc_root(void)

It would be good to add some comments for this function to indicate that
this func intends to enable BTF generation for kfuncs bpf_cast_to_kern_ctx()
and bpf_rdonly_cast() which are necessary for the above two programs.

> +{
> +	bpf_cast_to_kern_ctx(0);
> +	bpf_rdonly_cast(0, 0);
> +}
> +
>   char _license[] SEC("license") = "GPL";