bpf: verifier: randomize high 32-bit when BPF_F_TEST_RND_HI32 is set

This patch randomizes high 32-bit of a definition when BPF_F_TEST_RND_HI32
is set.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d4394a84b9eb73c7ea473017690bb9128ba04eb1..2778417e6e0c3d66516b446b9a52e81d60b73a11 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7640,33 +7640,79 @@ static int opt_remove_nops(struct bpf_verifier_env *env)
        return 0;
 }
 
-static int opt_subreg_zext_lo32(struct bpf_verifier_env *env)
+static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
+                                        const union bpf_attr *attr)
 {
+       struct bpf_insn *patch, zext_patch[2], rnd_hi32_patch[4];
        struct bpf_insn_aux_data *aux = env->insn_aux_data;
+       int i, patch_len, delta = 0, len = env->prog->len;
        struct bpf_insn *insns = env->prog->insnsi;
-       int i, delta = 0, len = env->prog->len;
-       struct bpf_insn zext_patch[2];
        struct bpf_prog *new_prog;
+       bool rnd_hi32;
 
+       rnd_hi32 = attr->prog_flags & BPF_F_TEST_RND_HI32;
        zext_patch[1] = BPF_ZEXT_REG(0);
+       rnd_hi32_patch[1] = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, 0);
+       rnd_hi32_patch[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_AX, 32);
+       rnd_hi32_patch[3] = BPF_ALU64_REG(BPF_OR, 0, BPF_REG_AX);
        for (i = 0; i < len; i++) {
                int adj_idx = i + delta;
                struct bpf_insn insn;
 
-               if (!aux[adj_idx].zext_dst)
+               insn = insns[adj_idx];
+               if (!aux[adj_idx].zext_dst) {
+                       u8 code, class;
+                       u32 imm_rnd;
+
+                       if (!rnd_hi32)
+                               continue;
+
+                       code = insn.code;
+                       class = BPF_CLASS(code);
+                       if (insn_no_def(&insn))
+                               continue;
+
+                       /* NOTE: arg "reg" (the fourth one) is only used for
+                        *       BPF_STX which has been ruled out in above
+                        *       check, it is safe to pass NULL here.
+                        */
+                       if (is_reg64(env, &insn, insn.dst_reg, NULL, DST_OP)) {
+                               if (class == BPF_LD &&
+                                   BPF_MODE(code) == BPF_IMM)
+                                       i++;
+                               continue;
+                       }
+
+                       /* ctx load could be transformed into wider load. */
+                       if (class == BPF_LDX &&
+                           aux[adj_idx].ptr_type == PTR_TO_CTX)
+                               continue;
+
+                       imm_rnd = get_random_int();
+                       rnd_hi32_patch[0] = insn;
+                       rnd_hi32_patch[1].imm = imm_rnd;
+                       rnd_hi32_patch[3].dst_reg = insn.dst_reg;
+                       patch = rnd_hi32_patch;
+                       patch_len = 4;
+                       goto apply_patch_buffer;
+               }
+
+               if (!bpf_jit_needs_zext())
                        continue;
 
-               insn = insns[adj_idx];
                zext_patch[0] = insn;
                zext_patch[1].dst_reg = insn.dst_reg;
                zext_patch[1].src_reg = insn.dst_reg;
-               new_prog = bpf_patch_insn_data(env, adj_idx, zext_patch, 2);
+               patch = zext_patch;
+               patch_len = 2;
+apply_patch_buffer:
+               new_prog = bpf_patch_insn_data(env, adj_idx, patch, patch_len);
                if (!new_prog)
                        return -ENOMEM;
                env->prog = new_prog;
                insns = new_prog->insnsi;
                aux = env->insn_aux_data;
-               delta += 2;
+               delta += patch_len - 1;
        }
 
        return 0;
@@ -8525,10 +8571,10 @@ skip_full_check:
        /* do 32-bit optimization after insn patching has done so those patched
         * insns could be handled correctly.
         */
-       if (ret == 0 && bpf_jit_needs_zext() &&
-           !bpf_prog_is_dev_bound(env->prog->aux)) {
-               ret = opt_subreg_zext_lo32(env);
-               env->prog->aux->verifier_zext = !ret;
+       if (ret == 0 && !bpf_prog_is_dev_bound(env->prog->aux)) {
+               ret = opt_subreg_zext_lo32_rnd_hi32(env, attr);
+               env->prog->aux->verifier_zext = bpf_jit_needs_zext() ? !ret
+                                                                    : false;
        }
 
        if (ret == 0)