From: Daniel Borkmann daniel@iogearbox.net
commit a7036191277f9fa68d92f2071ddc38c09b1e5ee5 upstream.
In 801c6058d14a ("bpf: Fix leakage of uninitialized bpf stack under speculation") we replaced masking logic with direct loads of immediates if the register is a known constant. Given in this case we do not apply any masking, there is also no reason for the operation to be truncated under the speculative domain.
Therefore, there is also zero reason for the verifier to branch-off and simulate this case, it only needs to do it for unknown but bounded scalars. As a side-effect, this also enables few test cases that were previously rejected due to simulation under zero truncation.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Piotr Krysiuk piotras@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org --- kernel/bpf/verifier.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f3f14519708d..4a3333039bf2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2169,8 +2169,12 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, /* If we're in commit phase, we're done here given we already * pushed the truncated dst_reg into the speculative verification * stack. + * + * Also, when register is a known constant, we rewrite register-based + * operation to immediate-based, and thus do not need masking (and as + * a consequence, do not need to simulate the zero-truncation either). */ - if (commit_window) + if (commit_window || off_is_imm) return 0;
/* Simulate and find potential out-of-bounds access under