Merge branch 'bpf-llvm-reg-alloc-patterns'

Alexei Starovoitov says:

====================
Make two verifier improvements:

- The llvm register allocator may use two different registers representing
  the same virtual register. Teach the verifier to recognize that.
- Track bounded scalar spill/fill.

The profiler[123] test in patch 3 will fail to load without patches 1 and 2.
The profiler[23] test may fail to load on older llvm due to speculative
code motion nd instruction combining optimizations that are fixed in
https://reviews.llvm.org/D85570

v1 -> v2:
  - fixed 32-bit mov issue spotted by John.
  - allowed r2=r1; r3=r2; sequence as suggested by John.
  - added comments, acks, more tests.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 65 insertions, 1 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 62b804651a48..f3e36eade3d4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2227,6 +2227,20 @@ static bool register_is_const(struct bpf_reg_state *reg)
 	return reg->type == SCALAR_VALUE && tnum_is_const(reg->var_off);
 }
 
+static bool __is_scalar_unbounded(struct bpf_reg_state *reg)
+{
+	return tnum_is_unknown(reg->var_off) &&
+	       reg->smin_value == S64_MIN && reg->smax_value == S64_MAX &&
+	       reg->umin_value == 0 && reg->umax_value == U64_MAX &&
+	       reg->s32_min_value == S32_MIN && reg->s32_max_value == S32_MAX &&
+	       reg->u32_min_value == 0 && reg->u32_max_value == U32_MAX;
+}
+
+static bool register_is_bounded(struct bpf_reg_state *reg)
+{
+	return reg->type == SCALAR_VALUE && !__is_scalar_unbounded(reg);
+}
+
 static bool __is_pointer_value(bool allow_ptr_leaks,
 			       const struct bpf_reg_state *reg)
 {
@@ -2278,7 +2292,7 @@ static int check_stack_write(struct bpf_verifier_env *env,
 	if (value_regno >= 0)
 		reg = &cur->regs[value_regno];
 
-	if (reg && size == BPF_REG_SIZE && register_is_const(reg) &&
+	if (reg && size == BPF_REG_SIZE && register_is_bounded(reg) &&
 	    !register_is_null(reg) && env->bpf_capable) {
 		if (dst_reg != BPF_REG_FP) {
 			/* The backtracking logic can only recognize explicit
@@ -6436,6 +6450,11 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
 	src_reg = NULL;
 	if (dst_reg->type != SCALAR_VALUE)
 		ptr_reg = dst_reg;
+	else
+		/* Make sure ID is cleared otherwise dst_reg min/max could be
+		 * incorrectly propagated into other registers by find_equal_scalars()
+		 */
+		dst_reg->id = 0;
 	if (BPF_SRC(insn->code) == BPF_X) {
 		src_reg = &regs[insn->src_reg];
 		if (src_reg->type != SCALAR_VALUE) {
@@ -6569,6 +6588,12 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 				/* case: R1 = R2
 				 * copy register state to dest reg
 				 */
+				if (src_reg->type == SCALAR_VALUE && !src_reg->id)
+					/* Assign src and dst registers the same ID
+					 * that will be used by find_equal_scalars()
+					 * to propagate min/max range.
+					 */
+					src_reg->id = ++env->id_gen;
 				*dst_reg = *src_reg;
 				dst_reg->live |= REG_LIVE_WRITTEN;
 				dst_reg->subreg_def = DEF_NOT_SUBREG;
@@ -6581,6 +6606,11 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 					return -EACCES;
 				} else if (src_reg->type == SCALAR_VALUE) {
 					*dst_reg = *src_reg;
+					/* Make sure ID is cleared otherwise
+					 * dst_reg min/max could be incorrectly
+					 * propagated into src_reg by find_equal_scalars()
+					 */
+					dst_reg->id = 0;
 					dst_reg->live |= REG_LIVE_WRITTEN;
 					dst_reg->subreg_def = env->insn_idx + 1;
 				} else {
@@ -7369,6 +7399,30 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn,
 	return true;
 }
 
+static void find_equal_scalars(struct bpf_verifier_state *vstate,
+			       struct bpf_reg_state *known_reg)
+{
+	struct bpf_func_state *state;
+	struct bpf_reg_state *reg;
+	int i, j;
+
+	for (i = 0; i <= vstate->curframe; i++) {
+		state = vstate->frame[i];
+		for (j = 0; j < MAX_BPF_REG; j++) {
+			reg = &state->regs[j];
+			if (reg->type == SCALAR_VALUE && reg->id == known_reg->id)
+				*reg = *known_reg;
+		}
+
+		bpf_for_each_spilled_reg(j, state, reg) {
+			if (!reg)
+				continue;
+			if (reg->type == SCALAR_VALUE && reg->id == known_reg->id)
+				*reg = *known_reg;
+		}
+	}
+}
+
 static int check_cond_jmp_op(struct bpf_verifier_env *env,
 			     struct bpf_insn *insn, int *insn_idx)
 {
@@ -7497,6 +7551,11 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 				reg_combine_min_max(&other_branch_regs[insn->src_reg],
 						    &other_branch_regs[insn->dst_reg],
 						    src_reg, dst_reg, opcode);
+			if (src_reg->id) {
+				find_equal_scalars(this_branch, src_reg);
+				find_equal_scalars(other_branch, &other_branch_regs[insn->src_reg]);
+			}
+
 		}
 	} else if (dst_reg->type == SCALAR_VALUE) {
 		reg_set_min_max(&other_branch_regs[insn->dst_reg],
@@ -7504,6 +7563,11 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 					opcode, is_jmp32);
 	}
 
+	if (dst_reg->type == SCALAR_VALUE && dst_reg->id) {
+		find_equal_scalars(this_branch, dst_reg);
+		find_equal_scalars(other_branch, &other_branch_regs[insn->dst_reg]);
+	}
+
 	/* detect if R == 0 where R is returned from bpf_map_lookup_elem().
 	 * NOTE: these optimizations below are related with pointer comparison
 	 *       which will never be JMP32.