diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/core.c | 4 | ||||
| -rw-r--r-- | kernel/bpf/verifier.c | 19 |
2 files changed, 22 insertions, 1 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index aa1e64196d8d..3a283bf97f2f 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2344,6 +2344,10 @@ bool __weak bpf_helper_changes_pkt_data(void *func) /* Return TRUE if the JIT backend wants verifier to enable sub-register usage * analysis code and wants explicit zero extension inserted by verifier. * Otherwise, return FALSE. + * + * The verifier inserts an explicit zero extension after BPF_CMPXCHGs even if + * you don't override this. JITs that don't want these extra insns can detect + * them using insn_is_zext. */ bool __weak bpf_jit_needs_zext(void) { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index bb3eaab934f3..c56e3fcb5f1a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -504,6 +504,13 @@ static bool is_ptr_cast_function(enum bpf_func_id func_id) func_id == BPF_FUNC_skc_to_tcp_request_sock; } +static bool is_cmpxchg_insn(const struct bpf_insn *insn) +{ + return BPF_CLASS(insn->code) == BPF_STX && + BPF_MODE(insn->code) == BPF_ATOMIC && + insn->imm == BPF_CMPXCHG; +} + /* string representation of 'enum bpf_reg_type' */ static const char * const reg_type_str[] = { [NOT_INIT] = "?", @@ -11067,7 +11074,17 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env, goto apply_patch_buffer; } - if (!bpf_jit_needs_zext()) + /* Add in an zero-extend instruction if a) the JIT has requested + * it or b) it's a CMPXCHG. + * + * The latter is because: BPF_CMPXCHG always loads a value into + * R0, therefore always zero-extends. However some archs' + * equivalent instruction only does this load when the + * comparison is successful. This detail of CMPXCHG is + * orthogonal to the general zero-extension behaviour of the + * CPU, so it's treated independently of bpf_jit_needs_zext. + */ + if (!bpf_jit_needs_zext() && !is_cmpxchg_insn(&insn)) continue; if (WARN_ON(load_reg == -1)) { |