Re: [PATCH v3 06/12] bpf: Return hashes of maps in BPF_OBJ_GET_INFO_BY_FD
From: Andrii Nakryiko <hidden>
Date: 2025-08-14 18:46:43
Also in:
bpf
On Wed, Aug 13, 2025 at 1:55 PM KP Singh [off-list ref] wrote:
Currently only array maps are supported, but the implementation can be extended for other maps and objects. The hash is memoized only for exclusive and frozen maps as their content is stable until the exclusive program modifies the map. This is required for BPF signing, enabling a trusted loader program to verify a map's integrity. The loader retrieves the map's runtime hash from the kernel and compares it against an expected hash computed at build time. Signed-off-by: KP Singh <kpsingh@kernel.org> --- include/linux/bpf.h | 3 +++ include/uapi/linux/bpf.h | 2 ++ kernel/bpf/arraymap.c | 13 +++++++++++ kernel/bpf/syscall.c | 23 +++++++++++++++++++ tools/include/uapi/linux/bpf.h | 2 ++ .../selftests/bpf/progs/verifier_map_ptr.c | 7 ++++-- 6 files changed, 48 insertions(+), 2 deletions(-)
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quoted hunk ↗ jump to hunk
struct bpf_btf_info {diff --git a/tools/testing/selftests/bpf/progs/verifier_map_ptr.c b/tools/testing/selftests/bpf/progs/verifier_map_ptr.c index 11a079145966..e2767d27d8aa 100644 --- a/tools/testing/selftests/bpf/progs/verifier_map_ptr.c +++ b/tools/testing/selftests/bpf/progs/verifier_map_ptr.c@@ -70,10 +70,13 @@ __naked void bpf_map_ptr_write_rejected(void) : __clobber_all); } +/* The first element of struct bpf_map is a SHA256 hash of 32 bytes, accessing + * into this array is valid. The opts field is now at offset 33. + */
Does hash have to be at the beginning of struct bpf_map? why not just put it at the end and not have to adjust any tests?.. (which now will fail on older kernel for no good reason, unless I miss something)
quoted hunk ↗ jump to hunk
SEC("socket") __description("bpf_map_ptr: read non-existent field rejected") __failure -__msg("cannot access ptr member ops with moff 0 in struct bpf_map with off 1 size 4") +__msg("cannot access ptr member ops with moff 32 in struct bpf_map with off 33 size 4") __failure_unpriv __msg_unpriv("access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN") __flag(BPF_F_ANY_ALIGNMENT)@@ -82,7 +85,7 @@ __naked void read_non_existent_field_rejected(void) asm volatile (" \ r6 = 0; \ r1 = %[map_array_48b] ll; \ - r6 = *(u32*)(r1 + 1); \ + r6 = *(u32*)(r1 + 33); \ r0 = 1; \ exit; \ " : --2.43.0