Martin and Vadim reported a verifier failure with bpf_dynptr usage.
The issue is mentioned but Vadim workarounded the issue with source
change ([1]). The below describes what is the issue and why there
is a verification failure.
int BPF_PROG(skb_crypto_setup) {
struct bpf_dynptr algo, key;
...
bpf_dynptr_from_mem(..., ..., 0, &algo);
...
}
The bpf program is using vmlinux.h, so we have the following definition in
vmlinux.h:
struct bpf_dynptr {
long: 64;
long: 64;
};
Note that in uapi header bpf.h, we have
struct bpf_dynptr {
long: 64;
long: 64;
} __attribute__((aligned(8)));
So we lost alignment information for struct bpf_dynptr by using vmlinux.h.
Let us take a look at a simple program below:
$ cat align.c
typedef unsigned long long __u64;
struct bpf_dynptr_no_align {
__u64 :64;
__u64 :64;
};
struct bpf_dynptr_yes_align {
__u64 :64;
__u64 :64;
} __attribute__((aligned(8)));
void bar(void *, void *);
int foo() {
struct bpf_dynptr_no_align a;
struct bpf_dynptr_yes_align b;
bar(&a, &b);
return 0;
}
$ clang --target=bpf -O2 -S -emit-llvm align.c
Look at the generated IR file align.ll:
...
%a = alloca %struct.bpf_dynptr_no_align, align 1
%b = alloca %struct.bpf_dynptr_yes_align, align 8
...
The compiler dictates the alignment for struct bpf_dynptr_no_align is 1 and
the alignment for struct bpf_dynptr_yes_align is 8. So theoretically compiler
could allocate variable %a with alignment 1 although in reallity the compiler
may choose a different alignment by considering other local variables.
In [1], the verification failure happens because variable 'algo' is allocated
on the stack with alignment 4 (fp-28). But the verifer wants its alignment
to be 8.
To fix the issue, the RFC patch ([1]) tried to add '__attribute__((aligned(8)))'
to struct bpf_dynptr plus other similar structs. Andrii suggested that
we could directly modify uapi struct with named fields like struct 'bpf_iter_num':
struct bpf_iter_num {
/* opaque iterator state; having __u64 here allows to preserve correct
* alignment requirements in vmlinux.h, generated from BTF
*/
__u64 __opaque[1];
} __attribute__((aligned(8)));
Indeed, adding named fields for those affected structs in this patch can preserve
alignment when bpf program references them in vmlinux.h. With this patch,
the verification failure in [1] can also be resolved.
[1] https://lore.kernel.org/bpf/1b100f73-7625-4c1f-3ae5-50ecf84d3ff0@linux.dev/
[2] https://lore.kernel.org/bpf/20231103055218.2395034-1-yonghong.song@linux.dev/
Cc: Vadim Fedorenko <vadfed@meta.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231104024900.1539182-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
The previous sync bpf-checkpoint-commit becomes invalid
due to upstream bpf tree force-push. This patch picked
a new valid commit as the bpf-checkpoint-commit so
the sync script can work with newer changes.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Without the change, we will have failures like below:
Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'
progs/getsockname_unix_prog.c:27:15: error: no member named 'uaddrlen' in 'struct bpf_sock_addr_kern'
if (sa_kern->uaddrlen != unaddrlen)
~~~~~~~ ^
1 error generated.
make: *** [Makefile:605: /home/runner/work/libbpf/libbpf/.kernel/tools/testing/selftests/bpf/getsockname_unix_prog.bpf.o] Error 1
make: *** Waiting for unfinished jobs....
Error: Process completed with exit code 2.
in Kernel 5.5.0 on ubuntu-20.04 + selftests
Manu Bretelle kindly helped regenerate the vmlinux.h from latest
bpf-next kernel for me.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Now 'BPF_MAP_TYPE_CGRP_STORAGE + local percpu ptr'
can cover all BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE functionality
and more. So mark BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE deprecated.
Also make changes in selftests/bpf/test_bpftool_synctypes.py
and selftest libbpf_str to fix otherwise test errors.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230827152837.2003563-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Add interpreter/jit support for new sign-extension load insns
which adds a new mode (BPF_MEMSX).
Also add verifier support to recognize these insns and to
do proper verification with new insns. In verifier, besides
to deduce proper bounds for the dst_reg, probed memory access
is also properly handled.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011156.3711870-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Yonghong Song