Merge branch 'verify scalar ids mapping in regsafe()'

Eduard Zingerman says:

====================
Update regsafe() to use check_ids() for scalar values.
Otherwise the following unsafe pattern is accepted by verifier:

  1: r9 = ... some pointer with range X ...
  2: r6 = ... unbound scalar ID=a ...
  3: r7 = ... unbound scalar ID=b ...
  4: if (r6 > r7) goto +1
  5: r6 = r7
  6: if (r6 > X) goto ...
  --- checkpoint ---
  7: r9 += r7
  8: *(u64 *)r9 = Y

This example is unsafe because not all execution paths verify r7 range.
Because of the jump at (4) the verifier would arrive at (6) in two states:
I.  r6{.id=b}, r7{.id=b} via path 1-6;
II. r6{.id=a}, r7{.id=b} via path 1-4, 6.

Currently regsafe() does not call check_ids() for scalar registers,
thus from POV of regsafe() states (I) and (II) are identical.

The change is split in two parts:
- patches #1,2: update for mark_chain_precision() to propagate
  precision marks through scalar IDs.
- patches #3,4: update for regsafe() to use a special version of
  check_ids() for precise scalar values.

Changelog:
- V5 -> V6:
  - check_ids() is modified to disallow mapping different 'old_id' to
    the same 'cur_id', check_scalar_ids() simplified (Andrii);
  - idset_push() updated to return -EFAULT instead of -1 (Andrii);
  - comments fixed in check_ids_in_regsafe() test case
    (Maxim Mikityanskiy);
  - fixed memset warning in states_equal() reported in [4].
- V4 -> V5 (all changes are based on feedback for V4 from Andrii):
  - mark_precise_scalar_ids() error code is updated to EFAULT;
  - bpf_verifier_env::idmap_scratch field type is changed to struct
    bpf_idmap to encapsulate temporary ID generation counter;
  - regsafe() is updated to call scalar_regs_exact() only for
    env->explore_alu_limits case (this had no measurable impact on
    verification duration when tested using veristat).
- V3 -> V4:
  - check_ids() in regsafe() is replaced by check_scalar_ids(),
    as discussed with Andrii in [3],
    Note: I did not transfer Andrii's ack for patch #3 from V3 because
          of the changes to the algorithm.
  - reg_id_scratch is renamed to idset_scratch;
  - mark_precise_scalar_ids() is modified to propagate error from
    idset_push();
  - test cases adjusted according to feedback from Andrii for V3.
- V2 -> V3:
  - u32_hashset for IDs used for range transfer is removed;
  - mark_chain_precision() is updated as discussed with Andrii in [2].
- V1 -> v2:
  - 'rold->precise' and 'rold->id' checks are dropped as unsafe
    (thanks to discussion with Yonghong);
  - patches #3,4 adding tracking of ids used for range transfer in
    order to mitigate performance impact.
- RFC -> V1:
  - Function verifier.c:mark_equal_scalars_as_read() is dropped,
    as it was an incorrect fix for problem solved by commit [3].
  - check_ids() is called only for precise scalar values.
  - Test case updated to use inline assembly.

[V1]  https://lore.kernel.org/bpf/20230526184126.3104040-1-eddyz87@gmail.com/
[V2]  https://lore.kernel.org/bpf/20230530172739.447290-1-eddyz87@gmail.com/
[V3]  https://lore.kernel.org/bpf/20230606222411.1820404-1-eddyz87@gmail.com/
[V4]  https://lore.kernel.org/bpf/20230609210143.2625430-1-eddyz87@gmail.com/
[V5]  https://lore.kernel.org/bpf/20230612160801.2804666-1-eddyz87@gmail.com/
[RFC] https://lore.kernel.org/bpf/20221128163442.280187-1-eddyz87@gmail.com/
[1]   https://gist.github.com/eddyz87/a32ea7e62a27d3c201117c9a39ab4286
[2]   https://lore.kernel.org/bpf/20230530172739.447290-1-eddyz87@gmail.com/T/#mc21009dcd8574b195c1860a98014bb037f16f450
[3]   https://lore.kernel.org/bpf/20230606222411.1820404-1-eddyz87@gmail.com/T/#m89da8eeb2fa8c9ca1202c5d0b6660e1f72e45e04
[4]   https://lore.kernel.org/oe-kbuild-all/202306131550.U3M9AJGm-lkp@intel.com/
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

5 files changed, 867 insertions, 33 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 5b11a3b0fec0..f70f9ac884d2 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -313,11 +313,6 @@ struct bpf_idx_pair {
 	u32 idx;
 };
 
-struct bpf_id_pair {
-	u32 old;
-	u32 cur;
-};
-
 #define MAX_CALL_FRAMES 8
 /* Maximum number of register states that can exist at once */
 #define BPF_ID_MAP_SIZE ((MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE) * MAX_CALL_FRAMES)
@@ -557,6 +552,21 @@ struct backtrack_state {
 	u64 stack_masks[MAX_CALL_FRAMES];
 };
 
+struct bpf_id_pair {
+	u32 old;
+	u32 cur;
+};
+
+struct bpf_idmap {
+	u32 tmp_id_gen;
+	struct bpf_id_pair map[BPF_ID_MAP_SIZE];
+};
+
+struct bpf_idset {
+	u32 count;
+	u32 ids[BPF_ID_MAP_SIZE];
+};
+
 /* single container for all structs
  * one verifier_env per bpf_check() call
  */
@@ -588,7 +598,10 @@ struct bpf_verifier_env {
 	const struct bpf_line_info *prev_linfo;
 	struct bpf_verifier_log log;
 	struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 1];
-	struct bpf_id_pair idmap_scratch[BPF_ID_MAP_SIZE];
+	union {
+		struct bpf_idmap idmap_scratch;
+		struct bpf_idset idset_scratch;
+	};
 	struct {
 		int *insn_state;
 		int *insn_stack;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1e38584d497c..fa43dc8e85b9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3779,6 +3779,96 @@ static void mark_all_scalars_imprecise(struct bpf_verifier_env *env, struct bpf_
 	}
 }
 
+static bool idset_contains(struct bpf_idset *s, u32 id)
+{
+	u32 i;
+
+	for (i = 0; i < s->count; ++i)
+		if (s->ids[i] == id)
+			return true;
+
+	return false;
+}
+
+static int idset_push(struct bpf_idset *s, u32 id)
+{
+	if (WARN_ON_ONCE(s->count >= ARRAY_SIZE(s->ids)))
+		return -EFAULT;
+	s->ids[s->count++] = id;
+	return 0;
+}
+
+static void idset_reset(struct bpf_idset *s)
+{
+	s->count = 0;
+}
+
+/* Collect a set of IDs for all registers currently marked as precise in env->bt.
+ * Mark all registers with these IDs as precise.
+ */
+static int mark_precise_scalar_ids(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
+{
+	struct bpf_idset *precise_ids = &env->idset_scratch;
+	struct backtrack_state *bt = &env->bt;
+	struct bpf_func_state *func;
+	struct bpf_reg_state *reg;
+	DECLARE_BITMAP(mask, 64);
+	int i, fr;
+
+	idset_reset(precise_ids);
+
+	for (fr = bt->frame; fr >= 0; fr--) {
+		func = st->frame[fr];
+
+		bitmap_from_u64(mask, bt_frame_reg_mask(bt, fr));
+		for_each_set_bit(i, mask, 32) {
+			reg = &func->regs[i];
+			if (!reg->id || reg->type != SCALAR_VALUE)
+				continue;
+			if (idset_push(precise_ids, reg->id))
+				return -EFAULT;
+		}
+
+		bitmap_from_u64(mask, bt_frame_stack_mask(bt, fr));
+		for_each_set_bit(i, mask, 64) {
+			if (i >= func->allocated_stack / BPF_REG_SIZE)
+				break;
+			if (!is_spilled_scalar_reg(&func->stack[i]))
+				continue;
+			reg = &func->stack[i].spilled_ptr;
+			if (!reg->id)
+				continue;
+			if (idset_push(precise_ids, reg->id))
+				return -EFAULT;
+		}
+	}
+
+	for (fr = 0; fr <= st->curframe; ++fr) {
+		func = st->frame[fr];
+
+		for (i = BPF_REG_0; i < BPF_REG_10; ++i) {
+			reg = &func->regs[i];
+			if (!reg->id)
+				continue;
+			if (!idset_contains(precise_ids, reg->id))
+				continue;
+			bt_set_frame_reg(bt, fr, i);
+		}
+		for (i = 0; i < func->allocated_stack / BPF_REG_SIZE; ++i) {
+			if (!is_spilled_scalar_reg(&func->stack[i]))
+				continue;
+			reg = &func->stack[i].spilled_ptr;
+			if (!reg->id)
+				continue;
+			if (!idset_contains(precise_ids, reg->id))
+				continue;
+			bt_set_frame_slot(bt, fr, i);
+		}
+	}
+
+	return 0;
+}
+
 /*
  * __mark_chain_precision() backtracks BPF program instruction sequence and
  * chain of verifier states making sure that register *regno* (if regno >= 0)
@@ -3910,6 +4000,31 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
 				bt->frame, last_idx, first_idx, subseq_idx);
 		}
 
+		/* If some register with scalar ID is marked as precise,
+		 * make sure that all registers sharing this ID are also precise.
+		 * This is needed to estimate effect of find_equal_scalars().
+		 * Do this at the last instruction of each state,
+		 * bpf_reg_state::id fields are valid for these instructions.
+		 *
+		 * Allows to track precision in situation like below:
+		 *
+		 *     r2 = unknown value
+		 *     ...
+		 *   --- state #0 ---
+		 *     ...
+		 *     r1 = r2                 // r1 and r2 now share the same ID
+		 *     ...
+		 *   --- state #1 {r1.id = A, r2.id = A} ---
+		 *     ...
+		 *     if (r2 > 10) goto exit; // find_equal_scalars() assigns range to r1
+		 *     ...
+		 *   --- state #2 {r1.id = A, r2.id = A} ---
+		 *     r3 = r10
+		 *     r3 += r1                // need to mark both r1 and r2
+		 */
+		if (mark_precise_scalar_ids(env, st))
+			return -EFAULT;
+
 		if (last_idx < 0) {
 			/* we are at the entry into subprog, which
 			 * is expected for global funcs, but only if
@@ -12819,12 +12934,14 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 		if (BPF_SRC(insn->code) == BPF_X) {
 			struct bpf_reg_state *src_reg = regs + insn->src_reg;
 			struct bpf_reg_state *dst_reg = regs + insn->dst_reg;
+			bool need_id = src_reg->type == SCALAR_VALUE && !src_reg->id &&
+				       !tnum_is_const(src_reg->var_off);
 
 			if (BPF_CLASS(insn->code) == BPF_ALU64) {
 				/* case: R1 = R2
 				 * copy register state to dest reg
 				 */
-				if (src_reg->type == SCALAR_VALUE && !src_reg->id)
+				if (need_id)
 					/* Assign src and dst registers the same ID
 					 * that will be used by find_equal_scalars()
 					 * to propagate min/max range.
@@ -12843,7 +12960,7 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 				} else if (src_reg->type == SCALAR_VALUE) {
 					bool is_src_reg_u32 = src_reg->umax_value <= U32_MAX;
 
-					if (is_src_reg_u32 && !src_reg->id)
+					if (is_src_reg_u32 && need_id)
 						src_reg->id = ++env->id_gen;
 					copy_register_state(dst_reg, src_reg);
 					/* Make sure ID is cleared if src_reg is not in u32 range otherwise
@@ -14999,8 +15116,9 @@ static bool range_within(struct bpf_reg_state *old,
  * So we look through our idmap to see if this old id has been seen before.  If
  * so, we require the new id to match; otherwise, we add the id pair to the map.
  */
-static bool check_ids(u32 old_id, u32 cur_id, struct bpf_id_pair *idmap)
+static bool check_ids(u32 old_id, u32 cur_id, struct bpf_idmap *idmap)
 {
+	struct bpf_id_pair *map = idmap->map;
 	unsigned int i;
 
 	/* either both IDs should be set or both should be zero */
@@ -15011,20 +15129,34 @@ static bool check_ids(u32 old_id, u32 cur_id, struct bpf_id_pair *idmap)
 		return true;
 
 	for (i = 0; i < BPF_ID_MAP_SIZE; i++) {
-		if (!idmap[i].old) {
+		if (!map[i].old) {
 			/* Reached an empty slot; haven't seen this id before */
-			idmap[i].old = old_id;
-			idmap[i].cur = cur_id;
+			map[i].old = old_id;
+			map[i].cur = cur_id;
 			return true;
 		}
-		if (idmap[i].old == old_id)
-			return idmap[i].cur == cur_id;
+		if (map[i].old == old_id)
+			return map[i].cur == cur_id;
+		if (map[i].cur == cur_id)
+			return false;
 	}
 	/* We ran out of idmap slots, which should be impossible */
 	WARN_ON_ONCE(1);
 	return false;
 }
 
+/* Similar to check_ids(), but allocate a unique temporary ID
+ * for 'old_id' or 'cur_id' of zero.
+ * This makes pairs like '0 vs unique ID', 'unique ID vs 0' valid.
+ */
+static bool check_scalar_ids(u32 old_id, u32 cur_id, struct bpf_idmap *idmap)
+{
+	old_id = old_id ? old_id : ++idmap->tmp_id_gen;
+	cur_id = cur_id ? cur_id : ++idmap->tmp_id_gen;
+
+	return check_ids(old_id, cur_id, idmap);
+}
+
 static void clean_func_state(struct bpf_verifier_env *env,
 			     struct bpf_func_state *st)
 {
@@ -15123,7 +15255,7 @@ next:
 
 static bool regs_exact(const struct bpf_reg_state *rold,
 		       const struct bpf_reg_state *rcur,
-		       struct bpf_id_pair *idmap)
+		       struct bpf_idmap *idmap)
 {
 	return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 &&
 	       check_ids(rold->id, rcur->id, idmap) &&
@@ -15132,7 +15264,7 @@ static bool regs_exact(const struct bpf_reg_state *rold,
 
 /* Returns true if (rold safe implies rcur safe) */
 static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
-		    struct bpf_reg_state *rcur, struct bpf_id_pair *idmap)
+		    struct bpf_reg_state *rcur, struct bpf_idmap *idmap)
 {
 	if (!(rold->live & REG_LIVE_READ))
 		/* explored state didn't use this */
@@ -15169,15 +15301,42 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 
 	switch (base_type(rold->type)) {
 	case SCALAR_VALUE:
-		if (regs_exact(rold, rcur, idmap))
-			return true;
-		if (env->explore_alu_limits)
-			return false;
+		if (env->explore_alu_limits) {
+			/* explore_alu_limits disables tnum_in() and range_within()
+			 * logic and requires everything to be strict
+			 */
+			return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 &&
+			       check_scalar_ids(rold->id, rcur->id, idmap);
+		}
 		if (!rold->precise)
 			return true;
-		/* new val must satisfy old val knowledge */
+		/* Why check_ids() for scalar registers?
+		 *
+		 * Consider the following BPF code:
+		 *   1: r6 = ... unbound scalar, ID=a ...
+		 *   2: r7 = ... unbound scalar, ID=b ...
+		 *   3: if (r6 > r7) goto +1
+		 *   4: r6 = r7
+		 *   5: if (r6 > X) goto ...
+		 *   6: ... memory operation using r7 ...
+		 *
+		 * First verification path is [1-6]:
+		 * - at (4) same bpf_reg_state::id (b) would be assigned to r6 and r7;
+		 * - at (5) r6 would be marked <= X, find_equal_scalars() would also mark
+		 *   r7 <= X, because r6 and r7 share same id.
+		 * Next verification path is [1-4, 6].
+		 *
+		 * Instruction (6) would be reached in two states:
+		 *   I.  r6{.id=b}, r7{.id=b} via path 1-6;
+		 *   II. r6{.id=a}, r7{.id=b} via path 1-4, 6.
+		 *
+		 * Use check_ids() to distinguish these states.
+		 * ---
+		 * Also verify that new value satisfies old value range knowledge.
+		 */
 		return range_within(rold, rcur) &&
-		       tnum_in(rold->var_off, rcur->var_off);
+		       tnum_in(rold->var_off, rcur->var_off) &&
+		       check_scalar_ids(rold->id, rcur->id, idmap);
 	case PTR_TO_MAP_KEY:
 	case PTR_TO_MAP_VALUE:
 	case PTR_TO_MEM:
@@ -15223,7 +15382,7 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 }
 
 static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
-		      struct bpf_func_state *cur, struct bpf_id_pair *idmap)
+		      struct bpf_func_state *cur, struct bpf_idmap *idmap)
 {
 	int i, spi;
 
@@ -15326,7 +15485,7 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
 }
 
 static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur,
-		    struct bpf_id_pair *idmap)
+		    struct bpf_idmap *idmap)
 {
 	int i;
 
@@ -15374,13 +15533,13 @@ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_stat
 
 	for (i = 0; i < MAX_BPF_REG; i++)
 		if (!regsafe(env, &old->regs[i], &cur->regs[i],
-			     env->idmap_scratch))
+			     &env->idmap_scratch))
 			return false;
 
-	if (!stacksafe(env, old, cur, env->idmap_scratch))
+	if (!stacksafe(env, old, cur, &env->idmap_scratch))
 		return false;
 
-	if (!refsafe(old, cur, env->idmap_scratch))
+	if (!refsafe(old, cur, &env->idmap_scratch))
 		return false;
 
 	return true;
@@ -15395,7 +15554,8 @@ static bool states_equal(struct bpf_verifier_env *env,
 	if (old->curframe != cur->curframe)
 		return false;
 
-	memset(env->idmap_scratch, 0, sizeof(env->idmap_scratch));
+	env->idmap_scratch.tmp_id_gen = env->id_gen;
+	memset(&env->idmap_scratch.map, 0, sizeof(env->idmap_scratch.map));
 
 	/* Verification state from speculative execution simulation
 	 * must never prune a non-speculative execution one.
@@ -15413,7 +15573,7 @@ static bool states_equal(struct bpf_verifier_env *env,
 		return false;
 
 	if (old->active_lock.id &&
-	    !check_ids(old->active_lock.id, cur->active_lock.id, env->idmap_scratch))
+	    !check_ids(old->active_lock.id, cur->active_lock.id, &env->idmap_scratch))
 		return false;
 
 	if (old->active_rcu_lock != cur->active_rcu_lock)
diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 531621adef42..070a13833c3f 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -50,6 +50,7 @@
 #include "verifier_regalloc.skel.h"
 #include "verifier_ringbuf.skel.h"
 #include "verifier_runtime_jit.skel.h"
+#include "verifier_scalar_ids.skel.h"
 #include "verifier_search_pruning.skel.h"
 #include "verifier_sock.skel.h"
 #include "verifier_spill_fill.skel.h"
@@ -150,6 +151,7 @@ void test_verifier_ref_tracking(void)         { RUN(verifier_ref_tracking); }
 void test_verifier_regalloc(void)             { RUN(verifier_regalloc); }
 void test_verifier_ringbuf(void)              { RUN(verifier_ringbuf); }
 void test_verifier_runtime_jit(void)          { RUN(verifier_runtime_jit); }
+void test_verifier_scalar_ids(void)           { RUN(verifier_scalar_ids); }
 void test_verifier_search_pruning(void)       { RUN(verifier_search_pruning); }
 void test_verifier_sock(void)                 { RUN(verifier_sock); }
 void test_verifier_spill_fill(void)           { RUN(verifier_spill_fill); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_scalar_ids.c b/tools/testing/selftests/bpf/progs/verifier_scalar_ids.c
new file mode 100644
index 000000000000..13b29a7faa71
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_scalar_ids.c
@@ -0,0 +1,659 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+/* Check that precision marks propagate through scalar IDs.
+ * Registers r{0,1,2} have the same scalar ID at the moment when r0 is
+ * marked to be precise, this mark is immediately propagated to r{1,2}.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("frame0: regs=r0,r1,r2 stack= before 4: (bf) r3 = r10")
+__msg("frame0: regs=r0,r1,r2 stack= before 3: (bf) r2 = r0")
+__msg("frame0: regs=r0,r1 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__msg("frame0: regs=r0 stack= before 0: (85) call bpf_ktime_get_ns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_same_state(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	/* force r0 to be precise, this immediately marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r3 = r10;"
+	"r3 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Same as precision_same_state, but mark propagates through state /
+ * parent state boundary.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("frame0: last_idx 6 first_idx 5 subseq_idx -1")
+__msg("frame0: regs=r0,r1,r2 stack= before 5: (bf) r3 = r10")
+__msg("frame0: parent state regs=r0,r1,r2 stack=:")
+__msg("frame0: regs=r0,r1,r2 stack= before 4: (05) goto pc+0")
+__msg("frame0: regs=r0,r1,r2 stack= before 3: (bf) r2 = r0")
+__msg("frame0: regs=r0,r1 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__msg("frame0: parent state regs=r0 stack=:")
+__msg("frame0: regs=r0 stack= before 0: (85) call bpf_ktime_get_ns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_cross_state(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	/* force checkpoint */
+	"goto +0;"
+	/* force r0 to be precise, this immediately marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r3 = r10;"
+	"r3 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Same as precision_same_state, but break one of the
+ * links, note that r1 is absent from regs=... in __msg below.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("frame0: regs=r0,r2 stack= before 5: (bf) r3 = r10")
+__msg("frame0: regs=r0,r2 stack= before 4: (b7) r1 = 0")
+__msg("frame0: regs=r0,r2 stack= before 3: (bf) r2 = r0")
+__msg("frame0: regs=r0 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__msg("frame0: regs=r0 stack= before 0: (85) call bpf_ktime_get_ns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_same_state_broken_link(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	/* break link for r1, this is the only line that differs
+	 * compared to the previous test
+	 */
+	"r1 = 0;"
+	/* force r0 to be precise, this immediately marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r3 = r10;"
+	"r3 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Same as precision_same_state_broken_link, but with state /
+ * parent state boundary.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("frame0: regs=r0,r2 stack= before 6: (bf) r3 = r10")
+__msg("frame0: regs=r0,r2 stack= before 5: (b7) r1 = 0")
+__msg("frame0: parent state regs=r0,r2 stack=:")
+__msg("frame0: regs=r0,r1,r2 stack= before 4: (05) goto pc+0")
+__msg("frame0: regs=r0,r1,r2 stack= before 3: (bf) r2 = r0")
+__msg("frame0: regs=r0,r1 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__msg("frame0: parent state regs=r0 stack=:")
+__msg("frame0: regs=r0 stack= before 0: (85) call bpf_ktime_get_ns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_cross_state_broken_link(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	/* force checkpoint, although link between r1 and r{0,2} is
+	 * broken by the next statement current precision tracking
+	 * algorithm can't react to it and propagates mark for r1 to
+	 * the parent state.
+	 */
+	"goto +0;"
+	/* break link for r1, this is the only line that differs
+	 * compared to precision_cross_state()
+	 */
+	"r1 = 0;"
+	/* force r0 to be precise, this immediately marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r3 = r10;"
+	"r3 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Check that precision marks propagate through scalar IDs.
+ * Use the same scalar ID in multiple stack frames, check that
+ * precision information is propagated up the call stack.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("11: (0f) r2 += r1")
+/* Current state */
+__msg("frame2: last_idx 11 first_idx 10 subseq_idx -1")
+__msg("frame2: regs=r1 stack= before 10: (bf) r2 = r10")
+__msg("frame2: parent state regs=r1 stack=")
+/* frame1.r{6,7} are marked because mark_precise_scalar_ids()
+ * looks for all registers with frame2.r1.id in the current state
+ */
+__msg("frame1: parent state regs=r6,r7 stack=")
+__msg("frame0: parent state regs=r6 stack=")
+/* Parent state */
+__msg("frame2: last_idx 8 first_idx 8 subseq_idx 10")
+__msg("frame2: regs=r1 stack= before 8: (85) call pc+1")
+/* frame1.r1 is marked because of backtracking of call instruction */
+__msg("frame1: parent state regs=r1,r6,r7 stack=")
+__msg("frame0: parent state regs=r6 stack=")
+/* Parent state */
+__msg("frame1: last_idx 7 first_idx 6 subseq_idx 8")
+__msg("frame1: regs=r1,r6,r7 stack= before 7: (bf) r7 = r1")
+__msg("frame1: regs=r1,r6 stack= before 6: (bf) r6 = r1")
+__msg("frame1: parent state regs=r1 stack=")
+__msg("frame0: parent state regs=r6 stack=")
+/* Parent state */
+__msg("frame1: last_idx 4 first_idx 4 subseq_idx 6")
+__msg("frame1: regs=r1 stack= before 4: (85) call pc+1")
+__msg("frame0: parent state regs=r1,r6 stack=")
+/* Parent state */
+__msg("frame0: last_idx 3 first_idx 1 subseq_idx 4")
+__msg("frame0: regs=r0,r1,r6 stack= before 3: (bf) r6 = r0")
+__msg("frame0: regs=r0,r1 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_many_frames(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r6.id */
+	"r1 = r0;"
+	"r6 = r0;"
+	"call precision_many_frames__foo;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+static __naked __noinline __used
+void precision_many_frames__foo(void)
+{
+	asm volatile (
+	/* conflate one of the register numbers (r6) with outer frame,
+	 * to verify that those are tracked independently
+	 */
+	"r6 = r1;"
+	"r7 = r1;"
+	"call precision_many_frames__bar;"
+	"exit"
+	::: __clobber_all);
+}
+
+static __naked __noinline __used
+void precision_many_frames__bar(void)
+{
+	asm volatile (
+	/* force r1 to be precise, this immediately marks:
+	 * - bar frame r1
+	 * - foo frame r{1,6,7}
+	 * - main frame r{1,6}
+	 */
+	"r2 = r10;"
+	"r2 += r1;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+/* Check that scalars with the same IDs are marked precise on stack as
+ * well as in registers.
+ */
+SEC("socket")
+__success __log_level(2)
+/* foo frame */
+__msg("frame1: regs=r1 stack=-8,-16 before 9: (bf) r2 = r10")
+__msg("frame1: regs=r1 stack=-8,-16 before 8: (7b) *(u64 *)(r10 -16) = r1")
+__msg("frame1: regs=r1 stack=-8 before 7: (7b) *(u64 *)(r10 -8) = r1")
+__msg("frame1: regs=r1 stack= before 4: (85) call pc+2")
+/* main frame */
+__msg("frame0: regs=r0,r1 stack=-8 before 3: (7b) *(u64 *)(r10 -8) = r1")
+__msg("frame0: regs=r0,r1 stack= before 2: (bf) r1 = r0")
+__msg("frame0: regs=r0 stack= before 1: (57) r0 &= 255")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_stack(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == fp[-8].id */
+	"r1 = r0;"
+	"*(u64*)(r10 - 8) = r1;"
+	"call precision_stack__foo;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+static __naked __noinline __used
+void precision_stack__foo(void)
+{
+	asm volatile (
+	/* conflate one of the register numbers (r6) with outer frame,
+	 * to verify that those are tracked independently
+	 */
+	"*(u64*)(r10 - 8) = r1;"
+	"*(u64*)(r10 - 16) = r1;"
+	/* force r1 to be precise, this immediately marks:
+	 * - foo frame r1,fp{-8,-16}
+	 * - main frame r1,fp{-8}
+	 */
+	"r2 = r10;"
+	"r2 += r1;"
+	"exit"
+	::: __clobber_all);
+}
+
+/* Use two separate scalar IDs to check that these are propagated
+ * independently.
+ */
+SEC("socket")
+__success __log_level(2)
+/* r{6,7} */
+__msg("11: (0f) r3 += r7")
+__msg("frame0: regs=r6,r7 stack= before 10: (bf) r3 = r10")
+/* ... skip some insns ... */
+__msg("frame0: regs=r6,r7 stack= before 3: (bf) r7 = r0")
+__msg("frame0: regs=r0,r6 stack= before 2: (bf) r6 = r0")
+/* r{8,9} */
+__msg("12: (0f) r3 += r9")
+__msg("frame0: regs=r8,r9 stack= before 11: (0f) r3 += r7")
+/* ... skip some insns ... */
+__msg("frame0: regs=r8,r9 stack= before 7: (bf) r9 = r0")
+__msg("frame0: regs=r0,r8 stack= before 6: (bf) r8 = r0")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void precision_two_ids(void)
+{
+	asm volatile (
+	/* r6 = random number up to 0xff
+	 * r6.id == r7.id
+	 */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	"r6 = r0;"
+	"r7 = r0;"
+	/* same, but for r{8,9} */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	"r8 = r0;"
+	"r9 = r0;"
+	/* clear r0 id */
+	"r0 = 0;"
+	/* force checkpoint */
+	"goto +0;"
+	"r3 = r10;"
+	/* force r7 to be precise, this also marks r6 */
+	"r3 += r7;"
+	/* force r9 to be precise, this also marks r8 */
+	"r3 += r9;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Verify that check_ids() is used by regsafe() for scalars.
+ *
+ * r9 = ... some pointer with range X ...
+ * r6 = ... unbound scalar ID=a ...
+ * r7 = ... unbound scalar ID=b ...
+ * if (r6 > r7) goto +1
+ * r7 = r6
+ * if (r7 > X) goto exit
+ * r9 += r6
+ * ... access memory using r9 ...
+ *
+ * The memory access is safe only if r7 is bounded,
+ * which is true for one branch and not true for another.
+ */
+SEC("socket")
+__failure __msg("register with unbounded min value")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void check_ids_in_regsafe(void)
+{
+	asm volatile (
+	/* Bump allocated stack */
+	"r1 = 0;"
+	"*(u64*)(r10 - 8) = r1;"
+	/* r9 = pointer to stack */
+	"r9 = r10;"
+	"r9 += -8;"
+	/* r7 = ktime_get_ns() */
+	"call %[bpf_ktime_get_ns];"
+	"r7 = r0;"
+	/* r6 = ktime_get_ns() */
+	"call %[bpf_ktime_get_ns];"
+	"r6 = r0;"
+	/* if r6 > r7 is an unpredictable jump */
+	"if r6 > r7 goto l1_%=;"
+	"r7 = r6;"
+"l1_%=:"
+	/* if r7 > 4 ...; transfers range to r6 on one execution path
+	 * but does not transfer on another
+	 */
+	"if r7 > 4 goto l2_%=;"
+	/* Access memory at r9[r6], r6 is not always bounded */
+	"r9 += r6;"
+	"r0 = *(u8*)(r9 + 0);"
+"l2_%=:"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Similar to check_ids_in_regsafe.
+ * The l0 could be reached in two states:
+ *
+ *   (1) r6{.id=A}, r7{.id=A}, r8{.id=B}
+ *   (2) r6{.id=B}, r7{.id=A}, r8{.id=B}
+ *
+ * Where (2) is not safe, as "r7 > 4" check won't propagate range for it.
+ * This example would be considered safe without changes to
+ * mark_chain_precision() to track scalar values with equal IDs.
+ */
+SEC("socket")
+__failure __msg("register with unbounded min value")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void check_ids_in_regsafe_2(void)
+{
+	asm volatile (
+	/* Bump allocated stack */
+	"r1 = 0;"
+	"*(u64*)(r10 - 8) = r1;"
+	/* r9 = pointer to stack */
+	"r9 = r10;"
+	"r9 += -8;"
+	/* r8 = ktime_get_ns() */
+	"call %[bpf_ktime_get_ns];"
+	"r8 = r0;"
+	/* r7 = ktime_get_ns() */
+	"call %[bpf_ktime_get_ns];"
+	"r7 = r0;"
+	/* r6 = ktime_get_ns() */
+	"call %[bpf_ktime_get_ns];"
+	"r6 = r0;"
+	/* scratch .id from r0 */
+	"r0 = 0;"
+	/* if r6 > r7 is an unpredictable jump */
+	"if r6 > r7 goto l1_%=;"
+	/* tie r6 and r7 .id */
+	"r6 = r7;"
+"l0_%=:"
+	/* if r7 > 4 exit(0) */
+	"if r7 > 4 goto l2_%=;"
+	/* Access memory at r9[r6] */
+	"r9 += r6;"
+	"r0 = *(u8*)(r9 + 0);"
+"l2_%=:"
+	"r0 = 0;"
+	"exit;"
+"l1_%=:"
+	/* tie r6 and r8 .id */
+	"r6 = r8;"
+	"goto l0_%=;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Check that scalar IDs *are not* generated on register to register
+ * assignments if source register is a constant.
+ *
+ * If such IDs *are* generated the 'l1' below would be reached in
+ * two states:
+ *
+ *   (1) r1{.id=A}, r2{.id=A}
+ *   (2) r1{.id=C}, r2{.id=C}
+ *
+ * Thus forcing 'if r1 == r2' verification twice.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("11: (1d) if r3 == r4 goto pc+0")
+__msg("frame 0: propagating r3,r4")
+__msg("11: safe")
+__msg("processed 15 insns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void no_scalar_id_for_const(void)
+{
+	asm volatile (
+	"call %[bpf_ktime_get_ns];"
+	/* unpredictable jump */
+	"if r0 > 7 goto l0_%=;"
+	/* possibly generate same scalar ids for r3 and r4 */
+	"r1 = 0;"
+	"r1 = r1;"
+	"r3 = r1;"
+	"r4 = r1;"
+	"goto l1_%=;"
+"l0_%=:"
+	/* possibly generate different scalar ids for r3 and r4 */
+	"r1 = 0;"
+	"r2 = 0;"
+	"r3 = r1;"
+	"r4 = r2;"
+"l1_%=:"
+	/* predictable jump, marks r3 and r4 precise */
+	"if r3 == r4 goto +0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Same as no_scalar_id_for_const() but for 32-bit values */
+SEC("socket")
+__success __log_level(2)
+__msg("11: (1e) if w3 == w4 goto pc+0")
+__msg("frame 0: propagating r3,r4")
+__msg("11: safe")
+__msg("processed 15 insns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void no_scalar_id_for_const32(void)
+{
+	asm volatile (
+	"call %[bpf_ktime_get_ns];"
+	/* unpredictable jump */
+	"if r0 > 7 goto l0_%=;"
+	/* possibly generate same scalar ids for r3 and r4 */
+	"w1 = 0;"
+	"w1 = w1;"
+	"w3 = w1;"
+	"w4 = w1;"
+	"goto l1_%=;"
+"l0_%=:"
+	/* possibly generate different scalar ids for r3 and r4 */
+	"w1 = 0;"
+	"w2 = 0;"
+	"w3 = w1;"
+	"w4 = w2;"
+"l1_%=:"
+	/* predictable jump, marks r1 and r2 precise */
+	"if w3 == w4 goto +0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Check that unique scalar IDs are ignored when new verifier state is
+ * compared to cached verifier state. For this test:
+ * - cached state has no id on r1
+ * - new state has a unique id on r1
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("6: (25) if r6 > 0x7 goto pc+1")
+__msg("7: (57) r1 &= 255")
+__msg("8: (bf) r2 = r10")
+__msg("from 6 to 8: safe")
+__msg("processed 12 insns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void ignore_unique_scalar_ids_cur(void)
+{
+	asm volatile (
+	"call %[bpf_ktime_get_ns];"
+	"r6 = r0;"
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* r1.id == r0.id */
+	"r1 = r0;"
+	/* make r1.id unique */
+	"r0 = 0;"
+	"if r6 > 7 goto l0_%=;"
+	/* clear r1 id, but keep the range compatible */
+	"r1 &= 0xff;"
+"l0_%=:"
+	/* get here in two states:
+	 * - first: r1 has no id (cached state)
+	 * - second: r1 has a unique id (should be considered equivalent)
+	 */
+	"r2 = r10;"
+	"r2 += r1;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Check that unique scalar IDs are ignored when new verifier state is
+ * compared to cached verifier state. For this test:
+ * - cached state has a unique id on r1
+ * - new state has no id on r1
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("6: (25) if r6 > 0x7 goto pc+1")
+__msg("7: (05) goto pc+1")
+__msg("9: (bf) r2 = r10")
+__msg("9: safe")
+__msg("processed 13 insns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void ignore_unique_scalar_ids_old(void)
+{
+	asm volatile (
+	"call %[bpf_ktime_get_ns];"
+	"r6 = r0;"
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* r1.id == r0.id */
+	"r1 = r0;"
+	/* make r1.id unique */
+	"r0 = 0;"
+	"if r6 > 7 goto l1_%=;"
+	"goto l0_%=;"
+"l1_%=:"
+	/* clear r1 id, but keep the range compatible */
+	"r1 &= 0xff;"
+"l0_%=:"
+	/* get here in two states:
+	 * - first: r1 has a unique id (cached state)
+	 * - second: r1 has no id (should be considered equivalent)
+	 */
+	"r2 = r10;"
+	"r2 += r1;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Check that two different scalar IDs in a verified state can't be
+ * mapped to the same scalar ID in current state.
+ */
+SEC("socket")
+__success __log_level(2)
+/* The exit instruction should be reachable from two states,
+ * use two matches and "processed .. insns" to ensure this.
+ */
+__msg("13: (95) exit")
+__msg("13: (95) exit")
+__msg("processed 18 insns")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked void two_old_ids_one_cur_id(void)
+{
+	asm volatile (
+	/* Give unique scalar IDs to r{6,7} */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	"r6 = r0;"
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	"r7 = r0;"
+	"r0 = 0;"
+	/* Maybe make r{6,7} IDs identical */
+	"if r6 > r7 goto l0_%=;"
+	"goto l1_%=;"
+"l0_%=:"
+	"r6 = r7;"
+"l1_%=:"
+	/* Mark r{6,7} precise.
+	 * Get here in two states:
+	 * - first:  r6{.id=A}, r7{.id=B} (cached state)
+	 * - second: r6{.id=A}, r7{.id=A}
+	 * Currently we don't want to consider such states equivalent.
+	 * Thus "exit;" would be verified twice.
+	 */
+	"r2 = r10;"
+	"r2 += r6;"
+	"r2 += r7;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/verifier/precise.c b/tools/testing/selftests/bpf/verifier/precise.c
index b8c0aae8e7ec..99272bb890da 100644
--- a/tools/testing/selftests/bpf/verifier/precise.c
+++ b/tools/testing/selftests/bpf/verifier/precise.c
@@ -46,7 +46,7 @@
 	mark_precise: frame0: regs=r2 stack= before 20\
 	mark_precise: frame0: parent state regs=r2 stack=:\
 	mark_precise: frame0: last_idx 19 first_idx 10\
-	mark_precise: frame0: regs=r2 stack= before 19\
+	mark_precise: frame0: regs=r2,r9 stack= before 19\
 	mark_precise: frame0: regs=r9 stack= before 18\
 	mark_precise: frame0: regs=r8,r9 stack= before 17\
 	mark_precise: frame0: regs=r0,r9 stack= before 15\
@@ -106,10 +106,10 @@
 	mark_precise: frame0: regs=r2 stack= before 22\
 	mark_precise: frame0: parent state regs=r2 stack=:\
 	mark_precise: frame0: last_idx 20 first_idx 20\
-	mark_precise: frame0: regs=r2 stack= before 20\
-	mark_precise: frame0: parent state regs=r2 stack=:\
+	mark_precise: frame0: regs=r2,r9 stack= before 20\
+	mark_precise: frame0: parent state regs=r2,r9 stack=:\
 	mark_precise: frame0: last_idx 19 first_idx 17\
-	mark_precise: frame0: regs=r2 stack= before 19\
+	mark_precise: frame0: regs=r2,r9 stack= before 19\
 	mark_precise: frame0: regs=r9 stack= before 18\
 	mark_precise: frame0: regs=r8,r9 stack= before 17\
 	mark_precise: frame0: parent state regs= stack=:",