On 3/1/21 6:18 AM, Yonghong Song wrote:
On 2/28/21 2:30 AM, Yauheni Kaliuta wrote:The verifier test labelled "valid read map access into a read-only array 2" calls the bpf_csum_diff() helper and checks its return value. However, architecture implementations of csum_partial() (which is what the helper uses) differ in whether they fold the return value to 16 bit or not. For example, x86 version has: if (unlikely(odd)) { result = from32to16(result); result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); } while generic lib/checksum.c does: result = from32to16(result); if (odd) result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); This makes the helper return different values on different architectures, breaking the test on non-x86. To fix this, add anI remember there is a previous discussion for this issue, csum_diff() returns different results for different architecture? Daniel? Any conclusion how to deal with this?
I took in the test case fix for now. After getting cascading work for !x86-64, we can always revert this one again. Plan of action to resume this work was to at least update the other 64-bit archs successively to a no-fold variant as well, so their arch specific implementations can mimic what x86-64 is doing.
additional instruction to always mask the return value to 16 bits, and update the expected return value accordingly. Fixes: fb2abb73e575 ("bpf, selftest: test {rd, wr}only flags and direct value access") Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@xxxxxxxxxx> --- tools/testing/selftests/bpf/verifier/array_access.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/verifier/array_access.c b/tools/testing/selftests/bpf/verifier/array_access.c index bed53b561e04..1b138cd2b187 100644 --- a/tools/testing/selftests/bpf/verifier/array_access.c +++ b/tools/testing/selftests/bpf/verifier/array_access.c @@ -250,12 +250,13 @@ BPF_MOV64_IMM(BPF_REG_5, 0), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_csum_diff), + BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xffff), BPF_EXIT_INSN(), }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .fixup_map_array_ro = { 3 }, .result = ACCEPT, - .retval = -29, + .retval = 65507, }, { "invalid write map access into a read-only array 1",
