[PATCH bpf-next v4 0/6] Add cryptographic hash and signature verification kfuncs to BPF

Daniel Hodges
2026-01-05T17:39:35Z

This patch series enhances BPF's cryptographic functionality by introducing
kernel functions for SHA hashing and ECDSA signature verification. The changes
enable BPF programs to verify data integrity and authenticity across
networking, security, and observability use cases.

The series addresses two gaps in BPF's cryptographic toolkit:

1. Cryptographic hashing - supports content verification and message digest
preparation
2. Asymmetric signature verification - allows validation of signed data
without requiring private keys in the datapath

Use cases include:
- Verifying signed network packets or application data in XDP/TC programs
- Integrity checks within tracing and security monitoring
- Zero-trust security models with BPF-based credential verification
- Content-addressed storage in BPF-based filesystems

The implementation leverages existing BPF patterns: it uses bpf_dynptr for
memory safety, reuses kernel crypto libraries (lib/crypto/sha256.c and
crypto/ecdsa.c) rather than reimplementing algorithms, and provides
context-based APIs supporting multiple program types.

v2:
- Fixed redundant __bpf_dynptr_is_rdonly() checks (Vadim)
- Added BPF hash algorithm type registration module in crypto/ subsystem
- Added CONFIG_CRYPTO_HASH2 guards around bpf_crypto_hash() kfunc and its
BTF registration, matching the pattern used for CONFIG_CRYPTO_ECDSA
- Added mandatory digestsize validation for hash operations

v3:
- Fixed patch ordering - header changes now in separate first commit before
crypto module to ensure bisectability (bot+bpf-ci)
- Fixed type mismatch - changed u32 to u64 for dynptr sizes in
bpf_crypto_hash() to match __bpf_dynptr_size() return type (Mykyta)
- Added CONFIG_CRYPTO_ECDSA to selftest config (Song)
- Refactored test code duplication with setup_skel() helper (Song)
- Added copyright notices to all new files

v4:
- Reused common bpf_crypto_ctx structure for hash and signature operations
instead of separate context types (Song)
- Fixed integer truncation in bpf_crypto_hash when data_len > UINT_MAX
- Corrected KF_RCU flags for ECDSA kfuncs (only bpf_ecdsa_verify needs KF_RCU)
- Updated MAINTAINERS file in test patches
- Refactored selftests to use crypto_common.h for kfunc declarations

Daniel Hodges (6):
crypto: Add BPF hash algorithm type registration module
crypto: Add BPF signature algorithm type registration module
bpf: Add hash kfunc for cryptographic hashing
selftests/bpf: Add tests for bpf_crypto_hash kfunc
bpf: Add ECDSA signature verification kfuncs
selftests/bpf: Add tests for ECDSA signature verification kfuncs

MAINTAINERS | 6 +
crypto/Makefile | 6 +
crypto/bpf_crypto_shash.c | 96 +++++++++
crypto/bpf_crypto_sig.c | 60 ++++++
crypto/bpf_crypto_skcipher.c | 1 +
include/linux/bpf_crypto.h | 7 +
kernel/bpf/crypto.c | 193 +++++++++++++++++-
tools/testing/selftests/bpf/config | 3 +
.../selftests/bpf/prog_tests/crypto_hash.c | 147 +++++++++++++
.../selftests/bpf/prog_tests/ecdsa_verify.c | 75 +++++++
.../selftests/bpf/progs/crypto_common.h | 7 +
.../testing/selftests/bpf/progs/crypto_hash.c | 136 ++++++++++++
.../selftests/bpf/progs/ecdsa_verify.c | 157 ++++++++++++++
13 files changed, 886 insertions(+), 8 deletions(-)
create mode 100644 crypto/bpf_crypto_shash.c
create mode 100644 crypto/bpf_crypto_sig.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/crypto_hash.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/ecdsa_verify.c
create mode 100644 tools/testing/selftests/bpf/progs/crypto_hash.c
create mode 100644 tools/testing/selftests/bpf/progs/ecdsa_verify.c

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2.51.0