[PATCH bpf-next v3 0/6] Fix invariant violations and improve branch detection

[PATCH bpf-next v3 0/6] Fix invariant violations and improve branch detection

[Paul Chaignon]

This patchset fixes invariant violations on register bounds. These
invariant violations cause a warning and happen when reg_bounds_sync is
trying to refine register bounds while walking an impossible branch.

This patchset takes this situation as an opportunity to improve
verification performance. That is, the verifier will use the invariant
violations as a signal that a branch cannot be taken and process it as
dead code.

This patchset implements this approach and covers it in selftests with
a new invariant violation case. Some of the logic in reg_bounds_sync
likely acts as a duplicate with logic from is_scalar_branch_taken. This
patchset does not attempt to remove superfluous logic from
is_scalar_branch_taken and leaves it to a future patchset (ex. once
syzbot has confirmed that all invariant violations are fixed).

In the future, there is also a potential opportunity to simplify
existing logic by merging reg_bounds_sync and range_bounds_violation
(have reg_bounds_sync error out on invariant violation). That is
however not needed to fix invariant violation, which we focus on in
this patchset.

Changes in v3:
  - Rename and refactor the helper functions checking for tnum-related
    invariant violations (Mykyta).
  - Small changes to comment style in verifier changes and new selftest
    (Mykyta).
  - Rebased.
Changes in v2:
  - Moved tmp registers to env in preparatory commit (Eduard).
  - Updated reg_bounds_sync to bail out in case of ill-formed
    registers, thus avoiding one set of invariant violation checks in
    simulate_both_branches_taken (Eduard).
  - Drop the Fixes tag to avoid misleading backporters (Shung-Hsi).
  - Improve wording of commit descriptions (Shung-Hsi, Hari).
  - Fix error in code comments (AI bot).
  - Rebased.

Harishankar Vishwanathan (3):
  bpf: Refactor reg_bounds_sanity_check
  bpf: Exit early if reg_bounds_sync gets invalid inputs
  bpf: Simulate branches to prune based on range violations

Paul Chaignon (3):
  bpf: Use bpf_verifier_env buffers for reg_set_min_max
  selftests/bpf: Cover invariant violation case from syzbot
  selftests/bpf: Remove invariant violation flags

 include/linux/bpf_verifier.h                  |   4 +-
 kernel/bpf/verifier.c                         | 201 ++++++++++--------
 .../selftests/bpf/progs/verifier_bounds.c     |  51 +++--
 3 files changed, 148 insertions(+), 108 deletions(-)

-- 
2.43.0

[PATCH bpf-next v3 1/6] bpf: Refactor reg_bounds_sanity_check

[Paul Chaignon]

From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>

This commit refactors reg_bounds_sanity_check to factor out the logic
that performs the sanity check from the logic that does the reporting.

Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/verifier.c | 64 +++++++++++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8c1cf2eb6cbb..760cd137bf3f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2804,39 +2804,55 @@ static void reg_bounds_sync(struct bpf_reg_state *reg)
 	__update_reg_bounds(reg);
 }
 
+static bool range_bounds_violation(struct bpf_reg_state *reg)
+{
+	return (reg->umin_value > reg->umax_value || reg->smin_value > reg->smax_value ||
+		reg->u32_min_value > reg->u32_max_value ||
+		reg->s32_min_value > reg->s32_max_value);
+}
+
+static bool const_tnum_range_mismatch(struct bpf_reg_state *reg)
+{
+	u64 uval = reg->var_off.value;
+	s64 sval = (s64)uval;
+
+	if (!tnum_is_const(reg->var_off))
+		return false;
+
+	return reg->umin_value != uval || reg->umax_value != uval ||
+	       reg->smin_value != sval || reg->smax_value != sval;
+}
+
+static bool const_tnum_range_mismatch_32(struct bpf_reg_state *reg)
+{
+	u32 uval32 = tnum_subreg(reg->var_off).value;
+	s32 sval32 = (s32)uval32;
+
+	if (!tnum_subreg_is_const(reg->var_off))
+		return false;
+
+	return reg->u32_min_value != uval32 || reg->u32_max_value != uval32 ||
+	       reg->s32_min_value != sval32 || reg->s32_max_value != sval32;
+}
+
 static int reg_bounds_sanity_check(struct bpf_verifier_env *env,
 				   struct bpf_reg_state *reg, const char *ctx)
 {
 	const char *msg;
 
-	if (reg->umin_value > reg->umax_value ||
-	    reg->smin_value > reg->smax_value ||
-	    reg->u32_min_value > reg->u32_max_value ||
-	    reg->s32_min_value > reg->s32_max_value) {
-		    msg = "range bounds violation";
-		    goto out;
+	if (range_bounds_violation(reg)) {
+		msg = "range bounds violation";
+		goto out;
 	}
 
-	if (tnum_is_const(reg->var_off)) {
-		u64 uval = reg->var_off.value;
-		s64 sval = (s64)uval;
-
-		if (reg->umin_value != uval || reg->umax_value != uval ||
-		    reg->smin_value != sval || reg->smax_value != sval) {
-			msg = "const tnum out of sync with range bounds";
-			goto out;
-		}
+	if (const_tnum_range_mismatch(reg)) {
+		msg = "const tnum out of sync with range bounds";
+		goto out;
 	}
 
-	if (tnum_subreg_is_const(reg->var_off)) {
-		u32 uval32 = tnum_subreg(reg->var_off).value;
-		s32 sval32 = (s32)uval32;
-
-		if (reg->u32_min_value != uval32 || reg->u32_max_value != uval32 ||
-		    reg->s32_min_value != sval32 || reg->s32_max_value != sval32) {
-			msg = "const subreg tnum out of sync with range bounds";
-			goto out;
-		}
+	if (const_tnum_range_mismatch_32(reg)) {
+		msg = "const subreg tnum out of sync with range bounds";
+		goto out;
 	}
 
 	return 0;
-- 
2.43.0

Re: [PATCH bpf-next v3 1/6] bpf: Refactor reg_bounds_sanity_check

[Eduard Zingerman]

On Thu, 2026-04-02 at 17:08 +0200, Paul Chaignon wrote:
> From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> 
> This commit refactors reg_bounds_sanity_check to factor out the logic
> that performs the sanity check from the logic that does the reporting.
> 
> Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

[PATCH bpf-next v3 2/6] bpf: Use bpf_verifier_env buffers for reg_set_min_max

[Paul Chaignon]

In a subsequent patch, the regs_refine_cond_op and reg_bounds_sync
functions will be called in is_branch_taken instead of reg_set_min_max,
to simulate each branch's outcome. Since they will run before we branch
out, these two functions will need to work on temporary registers for
the two branches.

This refactoring patch prepares for that change, by introducing the
temporary registers on bpf_verifier_env and using them in
reg_set_min_max.

This change also allows us to save one fake_reg slot as we don't need to
allocate an additional temporary buffer in case of a BPF_K condition.

Finally, you may notice that this patch removes the check for
"false_reg1 == false_reg2" in reg_set_min_max. That check was introduced
in commit d43ad9da8052 ("bpf: Skip bounds adjustment for conditional
jumps on same scalar register") to avoid an invariant violation. Given
that "env->false_reg1 == env->false_reg2" doesn't make sense and
invariant violations are addressed in a subsequent commit, this patch
just removes the check.

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Co-developed-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
---
 include/linux/bpf_verifier.h |  4 ++-
 kernel/bpf/verifier.c        | 64 +++++++++++++-----------------------
 2 files changed, 26 insertions(+), 42 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 090aa26d1c98..b129e0aaee20 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -837,7 +837,9 @@ struct bpf_verifier_env {
 	u64 scratched_stack_slots;
 	u64 prev_log_pos, prev_insn_print_pos;
 	/* buffer used to temporary hold constants as scalar registers */
-	struct bpf_reg_state fake_reg[2];
+	struct bpf_reg_state fake_reg[1];
+	/* buffers used to save updated reg states while simulating branches */
+	struct bpf_reg_state true_reg1, true_reg2, false_reg1, false_reg2;
 	/* buffer used to generate temporary string representations,
 	 * e.g., in reg_type_str() to generate reg_type string
 	 */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 760cd137bf3f..15defae1d7ed 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17253,10 +17253,6 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state
  * but we don't support that right now.
  */
 static int reg_set_min_max(struct bpf_verifier_env *env,
-			   struct bpf_reg_state *true_reg1,
-			   struct bpf_reg_state *true_reg2,
-			   struct bpf_reg_state *false_reg1,
-			   struct bpf_reg_state *false_reg2,
 			   u8 opcode, bool is_jmp32)
 {
 	int err;
@@ -17265,30 +17261,23 @@ static int reg_set_min_max(struct bpf_verifier_env *env,
 	 * variable offset from the compare (unless they were a pointer into
 	 * the same object, but we don't bother with that).
 	 */
-	if (false_reg1->type != SCALAR_VALUE || false_reg2->type != SCALAR_VALUE)
-		return 0;
-
-	/* We compute branch direction for same SCALAR_VALUE registers in
-	 * is_scalar_branch_taken(). For unknown branch directions (e.g., BPF_JSET)
-	 * on the same registers, we don't need to adjust the min/max values.
-	 */
-	if (false_reg1 == false_reg2)
+	if (env->false_reg1.type != SCALAR_VALUE || env->false_reg2.type != SCALAR_VALUE)
 		return 0;
 
 	/* fallthrough (FALSE) branch */
-	regs_refine_cond_op(false_reg1, false_reg2, rev_opcode(opcode), is_jmp32);
-	reg_bounds_sync(false_reg1);
-	reg_bounds_sync(false_reg2);
+	regs_refine_cond_op(&env->false_reg1, &env->false_reg2, rev_opcode(opcode), is_jmp32);
+	reg_bounds_sync(&env->false_reg1);
+	reg_bounds_sync(&env->false_reg2);
 
 	/* jump (TRUE) branch */
-	regs_refine_cond_op(true_reg1, true_reg2, opcode, is_jmp32);
-	reg_bounds_sync(true_reg1);
-	reg_bounds_sync(true_reg2);
-
-	err = reg_bounds_sanity_check(env, true_reg1, "true_reg1");
-	err = err ?: reg_bounds_sanity_check(env, true_reg2, "true_reg2");
-	err = err ?: reg_bounds_sanity_check(env, false_reg1, "false_reg1");
-	err = err ?: reg_bounds_sanity_check(env, false_reg2, "false_reg2");
+	regs_refine_cond_op(&env->true_reg1, &env->true_reg2, opcode, is_jmp32);
+	reg_bounds_sync(&env->true_reg1);
+	reg_bounds_sync(&env->true_reg2);
+
+	err = reg_bounds_sanity_check(env, &env->true_reg1, "true_reg1");
+	err = err ?: reg_bounds_sanity_check(env, &env->true_reg2, "true_reg2");
+	err = err ?: reg_bounds_sanity_check(env, &env->false_reg1, "false_reg1");
+	err = err ?: reg_bounds_sanity_check(env, &env->false_reg2, "false_reg2");
 	return err;
 }
 
@@ -17672,6 +17661,10 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 	}
 
 	is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
+	copy_register_state(&env->false_reg1, dst_reg);
+	copy_register_state(&env->false_reg2, src_reg);
+	copy_register_state(&env->true_reg1, dst_reg);
+	copy_register_state(&env->true_reg2, src_reg);
 	pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
 	if (pred >= 0) {
 		/* If we get here with a dst_reg pointer type it is because
@@ -17736,27 +17729,16 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 		return PTR_ERR(other_branch);
 	other_branch_regs = other_branch->frame[other_branch->curframe]->regs;
 
-	if (BPF_SRC(insn->code) == BPF_X) {
-		err = reg_set_min_max(env,
-				      &other_branch_regs[insn->dst_reg],
-				      &other_branch_regs[insn->src_reg],
-				      dst_reg, src_reg, opcode, is_jmp32);
-	} else /* BPF_SRC(insn->code) == BPF_K */ {
-		/* reg_set_min_max() can mangle the fake_reg. Make a copy
-		 * so that these are two different memory locations. The
-		 * src_reg is not used beyond here in context of K.
-		 */
-		memcpy(&env->fake_reg[1], &env->fake_reg[0],
-		       sizeof(env->fake_reg[0]));
-		err = reg_set_min_max(env,
-				      &other_branch_regs[insn->dst_reg],
-				      &env->fake_reg[0],
-				      dst_reg, &env->fake_reg[1],
-				      opcode, is_jmp32);
-	}
+	err = reg_set_min_max(env, opcode, is_jmp32);
 	if (err)
 		return err;
 
+	copy_register_state(dst_reg, &env->false_reg1);
+	copy_register_state(src_reg, &env->false_reg2);
+	copy_register_state(&other_branch_regs[insn->dst_reg], &env->true_reg1);
+	if (BPF_SRC(insn->code) == BPF_X)
+		copy_register_state(&other_branch_regs[insn->src_reg], &env->true_reg2);
+
 	if (BPF_SRC(insn->code) == BPF_X &&
 	    src_reg->type == SCALAR_VALUE && src_reg->id &&
 	    !WARN_ON_ONCE(src_reg->id != other_branch_regs[insn->src_reg].id)) {
-- 
2.43.0

[PATCH bpf-next v3 3/6] bpf: Exit early if reg_bounds_sync gets invalid inputs

[Paul Chaignon]

From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>

In the subsequent commit, to prune dead branches we will rely on
detecting ill-formed ranges using range_bounds_violations()
(e.g., umin > umax) after refining register bounds using
regs_refine_cond_op().

However, reg_bounds_sync() can sometimes "repair" ill-formed bounds,
potentially masking a violation that was produced by
regs_refine_cond_op().

This commit modifies reg_bounds_sync() to exit early if an invariant
violation is already present in the input.

This ensures ill-formed reg_states remain ill-formed after
reg_bounds_sync(), allowing simulate_both_branches_taken() to correctly
identify dead branches with a single check to range_bounds_violation().

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 15defae1d7ed..8215355f6be0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2788,8 +2788,13 @@ static void __reg_bound_offset(struct bpf_reg_state *reg)
 	reg->var_off = tnum_or(tnum_clear_subreg(var64_off), var32_off);
 }
 
+static bool range_bounds_violation(struct bpf_reg_state *reg);
+
 static void reg_bounds_sync(struct bpf_reg_state *reg)
 {
+	/* If the input reg_state is invalid, we can exit early */
+	if (range_bounds_violation(reg))
+		return;
 	/* We might have learned new bounds from the var_off. */
 	__update_reg_bounds(reg);
 	/* We might have learned something about the sign bit. */
-- 
2.43.0

Re: [PATCH bpf-next v3 3/6] bpf: Exit early if reg_bounds_sync gets invalid inputs

[Eduard Zingerman]

On Thu, 2026-04-02 at 17:10 +0200, Paul Chaignon wrote:
> From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> 
> In the subsequent commit, to prune dead branches we will rely on
> detecting ill-formed ranges using range_bounds_violations()
> (e.g., umin > umax) after refining register bounds using
> regs_refine_cond_op().
> 
> However, reg_bounds_sync() can sometimes "repair" ill-formed bounds,
> potentially masking a violation that was produced by
> regs_refine_cond_op().
> 
> This commit modifies reg_bounds_sync() to exit early if an invariant
> violation is already present in the input.
> 
> This ensures ill-formed reg_states remain ill-formed after
> reg_bounds_sync(), allowing simulate_both_branches_taken() to correctly
> identify dead branches with a single check to range_bounds_violation().
> 
> Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

[PATCH bpf-next v3 4/6] bpf: Simulate branches to prune based on range violations

[Paul Chaignon]

From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>

This patch fixes the invariant violations that can happen after we
refine ranges & tnum based on an incorrectly-detected branch condition.
For example, the branch is always true, but we miss it in
is_branch_taken; we then refine based on the branch being false and end
up with incoherent ranges (e.g. umax < umin).

To avoid this, we can simulate the refinement on both branches. More
specifically, this patch simulates both branches taken using
regs_refine_cond_op and reg_bounds_sync. If the resulting register
states are ill-formed on one of the branches, is_branch_taken can mark
that branch as "never taken".

On a more formal note, we can deduce a branch is not taken when
regs_refine_cond_op or reg_bounds_sync returns an ill-formed state
because the branch operators are sound (verified with Agni [1]).
Soundness means that the verifier is guaranteed to produce sound
outputs on the taken branches. On the non-taken branch (explored
because of imprecision in the bounds), the verifier is free to produce
any output. We use ill-formedness as a signal that the branch is dead
and prune that branch.

This patch moves the refinement logic for both branches from
reg_set_min_max to their own function, simulate_both_branches_taken,
which is called from is_scalar_branch_taken. As a result,
reg_set_min_max now only runs sanity checks and has been renamed to
reg_bounds_sanity_check_branches to reflect that.

We have had five patches fixing specific cases of invariant violations
in the past, all added with selftests:
- commit fbc7aef517d8 ("bpf: Fix u32/s32 bounds when ranges cross
  min/max boundary")
- commit efc11a667878 ("bpf: Improve bounds when tnum has a single
  possible value")
- commit f41345f47fb2 ("bpf: Use tnums for JEQ/JNE is_branch_taken
  logic")
- commit 00bf8d0c6c9b ("bpf: Improve bounds when s64 crosses sign
  boundary")
- commit 6279846b9b25 ("bpf: Forget ranges when refining tnum after
  JSET")

To confirm that this patch addresses all invariant violations, we have
also reverted those five commits and verified that their related
selftests don't cause any invariant violation warnings anymore. Those
selftests still fail but only because of misdetected branches or
less-precise bounds than expected. This demonstrates that the current
patch is enough to avoid the invariant violation warning AND that the
previous five patches are still useful to improve branch detection.

In addition to the selftests, this change was also tested with the
Cilium complexity test suite: all programs were successfully loaded and
it didn't change the number of processed instructions.

Link: https://github.com/bpfverif/agni [1]
Reported-by: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c950cc277150935cc0b5
Co-developed-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Co-developed-by: Srinivas Narayana <srinivas.narayana@rutgers.edu>
Signed-off-by: Srinivas Narayana <srinivas.narayana@rutgers.edu>
Co-developed-by: Santosh Nagarakatte <santosh.nagarakatte@rutgers.edu>
Signed-off-by: Santosh Nagarakatte <santosh.nagarakatte@rutgers.edu>
Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/verifier.c | 86 +++++++++++++++++++++++++------------------
 1 file changed, 51 insertions(+), 35 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8215355f6be0..a431b7d50e1b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16786,11 +16786,50 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
 	}));
 }
 
+static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
+				u8 opcode, bool is_jmp32);
+static u8 rev_opcode(u8 opcode);
+
+/*
+ * Learn more information about live branches by simulating refinement on both branches.
+ * regs_refine_cond_op() is sound, so producing ill-formed register bounds for the branch means
+ * that branch is dead.
+ */
+static int simulate_both_branches_taken(struct bpf_verifier_env *env, u8 opcode, bool is_jmp32)
+{
+	/* Fallthrough (FALSE) branch */
+	regs_refine_cond_op(&env->false_reg1, &env->false_reg2, rev_opcode(opcode), is_jmp32);
+	reg_bounds_sync(&env->false_reg1);
+	reg_bounds_sync(&env->false_reg2);
+	/*
+	 * If there is a range bounds violation in *any* of the abstract values in either
+	 * reg_states in the FALSE branch (i.e. reg1, reg2), the FALSE branch must be dead. Only
+	 * TRUE branch will be taken.
+	 */
+	if (range_bounds_violation(&env->false_reg1) || range_bounds_violation(&env->false_reg2))
+		return 1;
+
+	/* Jump (TRUE) branch */
+	regs_refine_cond_op(&env->true_reg1, &env->true_reg2, opcode, is_jmp32);
+	reg_bounds_sync(&env->true_reg1);
+	reg_bounds_sync(&env->true_reg2);
+	/*
+	 * If there is a range bounds violation in *any* of the abstract values in either
+	 * reg_states in the TRUE branch (i.e. true_reg1, true_reg2), the TRUE branch must be dead.
+	 * Only FALSE branch will be taken.
+	 */
+	if (range_bounds_violation(&env->true_reg1) || range_bounds_violation(&env->true_reg2))
+		return 0;
+
+	/* Both branches are possible, we can't determine which one will be taken. */
+	return -1;
+}
+
 /*
  * <reg1> <op> <reg2>, currently assuming reg2 is a constant
  */
-static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
-				  u8 opcode, bool is_jmp32)
+static int is_scalar_branch_taken(struct bpf_verifier_env *env, struct bpf_reg_state *reg1,
+				  struct bpf_reg_state *reg2, u8 opcode, bool is_jmp32)
 {
 	struct tnum t1 = is_jmp32 ? tnum_subreg(reg1->var_off) : reg1->var_off;
 	struct tnum t2 = is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_off;
@@ -16942,7 +16981,7 @@ static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_sta
 		break;
 	}
 
-	return -1;
+	return simulate_both_branches_taken(env, opcode, is_jmp32);
 }
 
 static int flip_opcode(u32 opcode)
@@ -17013,8 +17052,8 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg,
  * -1 - unknown. Example: "if (reg1 < 5)" is unknown when register value
  *      range [0,10]
  */
-static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
-			   u8 opcode, bool is_jmp32)
+static int is_branch_taken(struct bpf_verifier_env *env, struct bpf_reg_state *reg1,
+			   struct bpf_reg_state *reg2, u8 opcode, bool is_jmp32)
 {
 	if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is_jmp32)
 		return is_pkt_ptr_branch_taken(reg1, reg2, opcode);
@@ -17052,7 +17091,7 @@ static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg
 	}
 
 	/* now deal with two scalars, but not necessarily constants */
-	return is_scalar_branch_taken(reg1, reg2, opcode, is_jmp32);
+	return is_scalar_branch_taken(env, reg1, reg2, opcode, is_jmp32);
 }
 
 /* Opcode that corresponds to a *false* branch condition.
@@ -17143,8 +17182,8 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state
 			/* u32_min_value is not equal to 0xffffffff at this point,
 			 * because otherwise u32_max_value is 0xffffffff as well,
 			 * in such a case both reg1 and reg2 would be constants,
-			 * jump would be predicted and reg_set_min_max() won't
-			 * be called.
+			 * jump would be predicted and regs_refine_cond_op()
+			 * wouldn't be called.
 			 *
 			 * Same reasoning works for all {u,s}{min,max}{32,64} cases
 			 * below.
@@ -17251,34 +17290,11 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state
 	}
 }
 
-/* Adjusts the register min/max values in the case that the dst_reg and
- * src_reg are both SCALAR_VALUE registers (or we are simply doing a BPF_K
- * check, in which case we have a fake SCALAR_VALUE representing insn->imm).
- * Technically we can do similar adjustments for pointers to the same object,
- * but we don't support that right now.
- */
-static int reg_set_min_max(struct bpf_verifier_env *env,
-			   u8 opcode, bool is_jmp32)
+/* Check for invariant violations on the registers for both branches of a condition */
+static int regs_bounds_sanity_check_branches(struct bpf_verifier_env *env)
 {
 	int err;
 
-	/* If either register is a pointer, we can't learn anything about its
-	 * variable offset from the compare (unless they were a pointer into
-	 * the same object, but we don't bother with that).
-	 */
-	if (env->false_reg1.type != SCALAR_VALUE || env->false_reg2.type != SCALAR_VALUE)
-		return 0;
-
-	/* fallthrough (FALSE) branch */
-	regs_refine_cond_op(&env->false_reg1, &env->false_reg2, rev_opcode(opcode), is_jmp32);
-	reg_bounds_sync(&env->false_reg1);
-	reg_bounds_sync(&env->false_reg2);
-
-	/* jump (TRUE) branch */
-	regs_refine_cond_op(&env->true_reg1, &env->true_reg2, opcode, is_jmp32);
-	reg_bounds_sync(&env->true_reg1);
-	reg_bounds_sync(&env->true_reg2);
-
 	err = reg_bounds_sanity_check(env, &env->true_reg1, "true_reg1");
 	err = err ?: reg_bounds_sanity_check(env, &env->true_reg2, "true_reg2");
 	err = err ?: reg_bounds_sanity_check(env, &env->false_reg1, "false_reg1");
@@ -17670,7 +17686,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 	copy_register_state(&env->false_reg2, src_reg);
 	copy_register_state(&env->true_reg1, dst_reg);
 	copy_register_state(&env->true_reg2, src_reg);
-	pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
+	pred = is_branch_taken(env, dst_reg, src_reg, opcode, is_jmp32);
 	if (pred >= 0) {
 		/* If we get here with a dst_reg pointer type it is because
 		 * above is_branch_taken() special cased the 0 comparison.
@@ -17734,7 +17750,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 		return PTR_ERR(other_branch);
 	other_branch_regs = other_branch->frame[other_branch->curframe]->regs;
 
-	err = reg_set_min_max(env, opcode, is_jmp32);
+	err = regs_bounds_sanity_check_branches(env);
 	if (err)
 		return err;
 
-- 
2.43.0

Re: [PATCH bpf-next v3 4/6] bpf: Simulate branches to prune based on range violations

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1045 bytes --]

> Reported-by: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c950cc277150935cc0b5

This is a bug fix addressing verifier invariant violations (e.g.
umax < umin) triggered by syzbot. The v1 of this patch included a
Fixes: tag pointing to 5f99f312bd3b ("bpf: add register bounds sanity
checks and sanitization"), which was dropped after discussion about
whether it pointed to the root cause or the detection mechanism.

Would it make sense to include a Fixes: tag here? Even if 5f99f312bd3b
only surfaced the issue, having a tag helps stable backport tooling
identify where the fix is needed. Without it, automated stable processes
may not pick this up.

https://lore.kernel.org/bpf/swmeukekw55emiwcduoq4jpjk6hwqk7nzxbcs4xgw4mir5ldd7@mqyinrubwmlo/


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/23908257980

Re: [PATCH bpf-next v3 4/6] bpf: Simulate branches to prune based on range violations

[Paul Chaignon]

On Thu, Apr 02, 2026 at 04:28:30PM +0000, bot+bpf-ci@kernel.org wrote:
> > Reported-by: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=c950cc277150935cc0b5
> 
> This is a bug fix addressing verifier invariant violations (e.g.
> umax < umin) triggered by syzbot. The v1 of this patch included a
> Fixes: tag pointing to 5f99f312bd3b ("bpf: add register bounds sanity
> checks and sanitization"), which was dropped after discussion about
> whether it pointed to the root cause or the detection mechanism.
> 
> Would it make sense to include a Fixes: tag here? Even if 5f99f312bd3b
> only surfaced the issue, having a tag helps stable backport tooling
> identify where the fix is needed. Without it, automated stable processes
> may not pick this up.

We discussed it and considered it best to just drop the tag. We believe
the automated stable processes will likely still pick this up
automatically, and if not, we can always backport ourselves if we want.

> 
> https://lore.kernel.org/bpf/swmeukekw55emiwcduoq4jpjk6hwqk7nzxbcs4xgw4mir5ldd7@mqyinrubwmlo/
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/23908257980

Re: [PATCH bpf-next v3 4/6] bpf: Simulate branches to prune based on range violations

[Eduard Zingerman]

On Thu, 2026-04-02 at 17:10 +0200, Paul Chaignon wrote:
> From: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> 
> This patch fixes the invariant violations that can happen after we
> refine ranges & tnum based on an incorrectly-detected branch condition.
> For example, the branch is always true, but we miss it in
> is_branch_taken; we then refine based on the branch being false and end
> up with incoherent ranges (e.g. umax < umin).
> 
> To avoid this, we can simulate the refinement on both branches. More
> specifically, this patch simulates both branches taken using
> regs_refine_cond_op and reg_bounds_sync. If the resulting register
> states are ill-formed on one of the branches, is_branch_taken can mark
> that branch as "never taken".
> 
> On a more formal note, we can deduce a branch is not taken when
> regs_refine_cond_op or reg_bounds_sync returns an ill-formed state
> because the branch operators are sound (verified with Agni [1]).
> Soundness means that the verifier is guaranteed to produce sound
> outputs on the taken branches. On the non-taken branch (explored
> because of imprecision in the bounds), the verifier is free to produce
> any output. We use ill-formedness as a signal that the branch is dead
> and prune that branch.
> 
> This patch moves the refinement logic for both branches from
> reg_set_min_max to their own function, simulate_both_branches_taken,
> which is called from is_scalar_branch_taken. As a result,
> reg_set_min_max now only runs sanity checks and has been renamed to
> reg_bounds_sanity_check_branches to reflect that.
> 
> We have had five patches fixing specific cases of invariant violations
> in the past, all added with selftests:
> - commit fbc7aef517d8 ("bpf: Fix u32/s32 bounds when ranges cross
>   min/max boundary")
> - commit efc11a667878 ("bpf: Improve bounds when tnum has a single
>   possible value")
> - commit f41345f47fb2 ("bpf: Use tnums for JEQ/JNE is_branch_taken
>   logic")
> - commit 00bf8d0c6c9b ("bpf: Improve bounds when s64 crosses sign
>   boundary")
> - commit 6279846b9b25 ("bpf: Forget ranges when refining tnum after
>   JSET")
> 
> To confirm that this patch addresses all invariant violations, we have
> also reverted those five commits and verified that their related
> selftests don't cause any invariant violation warnings anymore. Those
> selftests still fail but only because of misdetected branches or
> less-precise bounds than expected. This demonstrates that the current
> patch is enough to avoid the invariant violation warning AND that the
> previous five patches are still useful to improve branch detection.
> 
> In addition to the selftests, this change was also tested with the
> Cilium complexity test suite: all programs were successfully loaded and
> it didn't change the number of processed instructions.
> 
> Link: https://github.com/bpfverif/agni [1]
> Reported-by: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c950cc277150935cc0b5
> Co-developed-by: Paul Chaignon <paul.chaignon@gmail.com>
> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
> Co-developed-by: Srinivas Narayana <srinivas.narayana@rutgers.edu>
> Signed-off-by: Srinivas Narayana <srinivas.narayana@rutgers.edu>
> Co-developed-by: Santosh Nagarakatte <santosh.nagarakatte@rutgers.edu>
> Signed-off-by: Santosh Nagarakatte <santosh.nagarakatte@rutgers.edu>
> Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

[PATCH bpf-next v3 5/6] selftests/bpf: Cover invariant violation case from syzbot

[Paul Chaignon]

This patch adds a selftest for the change in the previous patch. The
selftest is derived from a syzbot reproducer from [1] (among the 22
reproducers on that page, only 4 still reproduced on latest bpf tree,
all being small variants of the same invariant violation).

The test case failure without the previous patch is shown below.

  0: R1=ctx() R10=fp0
  0: (85) call bpf_get_prandom_u32#7    ; R0=scalar()
  1: (bf) r5 = r0                       ; R0=scalar(id=1) R5=scalar(id=1)
  2: (57) r5 &= -4                      ; R5=scalar(smax=0x7ffffffffffffffc,umax=0xfffffffffffffffc,smax32=0x7ffffffc,umax32=0xfffffffc,var_off=(0x0; 0xfffffffffffffffc))
  3: (bf) r7 = r0                       ; R0=scalar(id=1) R7=scalar(id=1)
  4: (57) r7 &= 1                       ; R7=scalar(smin=smin32=0,smax=umax=smax32=umax32=1,var_off=(0x0; 0x1))
  5: (07) r7 += -43                     ; R7=scalar(smin=smin32=-43,smax=smax32=-42,umin=0xffffffffffffffd5,umax=0xffffffffffffffd6,umin32=0xffffffd5,umax32=0xffffffd6,var_off=(0xffffffffffffffd4; 0x3))
  6: (5e) if w5 != w7 goto pc+1
  verifier bug: REG INVARIANTS VIOLATION (false_reg1): range bounds violation u64=[0xffffffd5, 0xffffffffffffffd4] s64=[0x80000000ffffffd5, 0x7fffffffffffffd4] u32=[0xffffffd5, 0xffffffd4] s32=[0xffffffd5, 0xffffffd4] var_off=(0xffffffd4, 0xffffffff00000000)

R5 and R7 are prepared such that their tnums intersection results in a
known constant but that constant isn't within R7's u32 bounds.
is_branch_taken isn't able to detect this case today, so the verifier
walks the impossible fallthrough branch. After regs_refine_cond_op and
reg_bounds_sync refine R5 on the assumption that the branch is taken,
the impossibility becomes apparent and results in an invariant violation
for R5: umin32 is greater than umax32.

The previous patch fixes this by using regs_refine_cond_op and
reg_bounds_sync in is_branch_taken to detect the impossible branch. The
fallthrough branch is therefore correctly detected as dead code.

Link: https://syzkaller.appspot.com/bug?extid=c950cc277150935cc0b5 [1]
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 .../selftests/bpf/progs/verifier_bounds.c     | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
index bb20f0f06f05..df7c62a12318 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
@@ -2165,4 +2165,33 @@ l0_%=:	r0 = 0;						\
 	: __clobber_all);
 }
 
+/*
+ * Last jump can be detected as always taken because the intersection of R5 and
+ * R7 32bit tnums produces a constant that isn't within R7's s32 bounds.
+ */
+SEC("socket")
+__description("dead branch: tnums give impossible constant if equal")
+__success
+__flag(BPF_F_TEST_REG_INVARIANTS)
+__naked void tnums_equal_impossible_constant(void *ctx)
+{
+	asm volatile("						\
+	call %[bpf_get_prandom_u32];				\
+	r5 = r0;						\
+	/* Set r5's var_off32 to (0; 0xfffffffc) */		\
+	r5 &= 0xfffffffffffffffc;				\
+	r7 = r0;						\
+	/* Set r7's var_off32 to (0x0; 0x1) */			\
+	r7 &= 0x1;						\
+	/* Now, s32=[-43; -42], var_off32=(0xffffffd4; 0x3) */	\
+	r7 += -43;						\
+	/* On fallthrough, var_off32=-44, not in s32 */		\
+	if w5 != w7 goto +1;					\
+	r10 = 0;						\
+	exit;							\
+"	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0

[PATCH bpf-next v3 6/6] selftests/bpf: Remove invariant violation flags

[Paul Chaignon]

With the changes to the verifier in previous commits, we're not
expecting any invariant violations anymore. We should therefore always
enable BPF_F_TEST_REG_INVARIANTS to fail on invariant violations. Turns
out that's already the case and we've been explicitly setting this flag
in selftests when it wasn't necessary. This commit removes those flags
from selftests, which should hopefully make clearer that it's always
enabled.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 .../selftests/bpf/progs/verifier_bounds.c     | 24 ++++++-------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c
index df7c62a12318..c1ae013dee29 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bounds.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c
@@ -1066,7 +1066,6 @@ l0_%=:	r0 = 0;						\
 SEC("xdp")
 __description("bound check with JMP_JSLT for crossing 64-bit signed boundary")
 __success __retval(0)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void crossing_64_bit_signed_boundary_2(void)
 {
 	asm volatile ("					\
@@ -1148,7 +1147,6 @@ l0_%=:	r0 = 0;						\
 SEC("xdp")
 __description("bound check with JMP32_JSLT for crossing 32-bit signed boundary")
 __success __retval(0)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void crossing_32_bit_signed_boundary_2(void)
 {
 	asm volatile ("					\
@@ -1536,7 +1534,7 @@ __naked void sub32_partial_overflow(void)
 SEC("socket")
 __description("dead branch on jset, does not result in invariants violation error")
 __success __log_level(2)
-__retval(0) __flag(BPF_F_TEST_REG_INVARIANTS)
+__retval(0)
 __naked void jset_range_analysis(void)
 {
 	asm volatile ("			\
@@ -1572,7 +1570,7 @@ l0_%=:	r0 = 0;				\
  */
 SEC("socket")
 __description("bounds deduction cross sign boundary, negative overlap")
-__success __log_level(2) __flag(BPF_F_TEST_REG_INVARIANTS)
+__success __log_level(2)
 __msg("7: (1f) r0 -= r6 {{.*}} R0=scalar(smin=smin32=-655,smax=smax32=-146,umin=0xfffffffffffffd71,umax=0xffffffffffffff6e,umin32=0xfffffd71,umax32=0xffffff6e,var_off=(0xfffffffffffffc00; 0x3ff))")
 __retval(0)
 __naked void bounds_deduct_negative_overlap(void)
@@ -1616,7 +1614,7 @@ l0_%=:	r0 = 0;				\
  */
 SEC("socket")
 __description("bounds deduction cross sign boundary, positive overlap")
-__success __log_level(2) __flag(BPF_F_TEST_REG_INVARIANTS)
+__success __log_level(2)
 __msg("3: (2d) if r0 > r1 {{.*}} R0=scalar(smin=smin32=0,smax=umax=smax32=umax32=127,var_off=(0x0; 0x7f))")
 __retval(0)
 __naked void bounds_deduct_positive_overlap(void)
@@ -1649,7 +1647,7 @@ l0_%=:	r0 = 0;				\
  */
 SEC("socket")
 __description("bounds deduction cross sign boundary, two overlaps")
-__failure __flag(BPF_F_TEST_REG_INVARIANTS)
+__failure
 __msg("3: (2d) if r0 > r1 {{.*}} R0=scalar(smin=smin32=-128,smax=smax32=127,umax=0xffffffffffffff80)")
 __msg("frame pointer is read only")
 __naked void bounds_deduct_two_overlaps(void)
@@ -1713,7 +1711,7 @@ SEC("socket")
 __description("conditional jump on same register, branch taken")
 __not_msg("20: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__retval(0) __flag(BPF_F_TEST_REG_INVARIANTS)
+__retval(0)
 __naked void condition_jump_on_same_register(void *ctx)
 {
 	asm volatile("			\
@@ -1748,7 +1746,7 @@ SEC("socket")
 __description("jset on same register, constant value branch taken")
 __not_msg("7: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__retval(0) __flag(BPF_F_TEST_REG_INVARIANTS)
+__retval(0)
 __naked void jset_on_same_register_1(void *ctx)
 {
 	asm volatile("			\
@@ -1770,7 +1768,7 @@ SEC("socket")
 __description("jset on same register, scalar value branch taken")
 __not_msg("12: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__retval(0) __flag(BPF_F_TEST_REG_INVARIANTS)
+__retval(0)
 __naked void jset_on_same_register_2(void *ctx)
 {
 	asm volatile("			\
@@ -1800,7 +1798,6 @@ __description("jset on same register, scalar value unknown branch 1")
 __msg("3: (b7) r0 = 0 {{.*}} R0=0")
 __msg("5: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void jset_on_same_register_3(void *ctx)
 {
 	asm volatile("			\
@@ -1822,7 +1819,6 @@ __description("jset on same register, scalar value unknown branch 2")
 __msg("4: (b7) r0 = 0 {{.*}} R0=0")
 __msg("6: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void jset_on_same_register_4(void *ctx)
 {
 	asm volatile("			\
@@ -1845,7 +1841,6 @@ __description("jset on same register, scalar value unknown branch 3")
 __msg("4: (b7) r0 = 0 {{.*}} R0=0")
 __msg("6: (b7) r0 = 1 {{.*}} R0=1")
 __success __log_level(2)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void jset_on_same_register_5(void *ctx)
 {
 	asm volatile("			\
@@ -1877,7 +1872,6 @@ SEC("socket")
 __description("bounds refinement with single-value tnum on umax")
 __msg("3: (15) if r0 == 0xe0 {{.*}} R0=240")
 __success __log_level(2)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void bounds_refinement_tnum_umax(void *ctx)
 {
 	asm volatile("			\
@@ -1907,7 +1901,6 @@ SEC("socket")
 __description("bounds refinement with single-value tnum on umin")
 __msg("3: (15) if r0 == 0xf0 {{.*}} R0=224")
 __success __log_level(2)
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void bounds_refinement_tnum_umin(void *ctx)
 {
 	asm volatile("			\
@@ -2002,7 +1995,6 @@ __naked void bounds_refinement_multiple_overlaps(void *ctx)
 
 SEC("socket")
 __success
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void signed_unsigned_intersection32_case1(void *ctx)
 {
 	asm volatile("									\
@@ -2020,7 +2012,6 @@ __naked void signed_unsigned_intersection32_case1(void *ctx)
 
 SEC("socket")
 __success
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void signed_unsigned_intersection32_case2(void *ctx)
 {
 	asm volatile("									\
@@ -2172,7 +2163,6 @@ l0_%=:	r0 = 0;						\
 SEC("socket")
 __description("dead branch: tnums give impossible constant if equal")
 __success
-__flag(BPF_F_TEST_REG_INVARIANTS)
 __naked void tnums_equal_impossible_constant(void *ctx)
 {
 	asm volatile("						\
-- 
2.43.0

Re: [PATCH bpf-next v3 0/6] Fix invariant violations and improve branch detection

[Eduard Zingerman]

On Thu, 2026-04-02 at 17:07 +0200, Paul Chaignon wrote:
> This patchset fixes invariant violations on register bounds. These
> invariant violations cause a warning and happen when reg_bounds_sync is
> trying to refine register bounds while walking an impossible branch.
> 
> This patchset takes this situation as an opportunity to improve
> verification performance. That is, the verifier will use the invariant
> violations as a signal that a branch cannot be taken and process it as
> dead code.
> 
> This patchset implements this approach and covers it in selftests with
> a new invariant violation case. Some of the logic in reg_bounds_sync
> likely acts as a duplicate with logic from is_scalar_branch_taken. This
> patchset does not attempt to remove superfluous logic from
> is_scalar_branch_taken and leaves it to a future patchset (ex. once
> syzbot has confirmed that all invariant violations are fixed).
> 
> In the future, there is also a potential opportunity to simplify
> existing logic by merging reg_bounds_sync and range_bounds_violation
> (have reg_bounds_sync error out on invariant violation). That is
> however not needed to fix invariant violation, which we focus on in
> this patchset.
> 
> Changes in v3:
>   - Rename and refactor the helper functions checking for tnum-related
>     invariant violations (Mykyta).
>   - Small changes to comment style in verifier changes and new selftest
>     (Mykyta).
>   - Rebased.
> Changes in v2:
>   - Moved tmp registers to env in preparatory commit (Eduard).
>   - Updated reg_bounds_sync to bail out in case of ill-formed
>     registers, thus avoiding one set of invariant violation checks in
>     simulate_both_branches_taken (Eduard).
>   - Drop the Fixes tag to avoid misleading backporters (Shung-Hsi).
>   - Improve wording of commit descriptions (Shung-Hsi, Hari).
>   - Fix error in code comments (AI bot).
>   - Rebased.

Thank you for addressing this issue, let's land this.
Please proceed with the followup covering tnum checks,
so that we can be finally sure that there are no
more invariant violations possible.

Re: [PATCH bpf-next v3 0/6] Fix invariant violations and improve branch detection

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 2 Apr 2026 17:07:25 +0200 you wrote:
> This patchset fixes invariant violations on register bounds. These
> invariant violations cause a warning and happen when reg_bounds_sync is
> trying to refine register bounds while walking an impossible branch.
> 
> This patchset takes this situation as an opportunity to improve
> verification performance. That is, the verifier will use the invariant
> violations as a signal that a branch cannot be taken and process it as
> dead code.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v3,1/6] bpf: Refactor reg_bounds_sanity_check
    https://git.kernel.org/bpf/bpf-next/c/a1311b94ef85
  - [bpf-next,v3,2/6] bpf: Use bpf_verifier_env buffers for reg_set_min_max
    https://git.kernel.org/bpf/bpf-next/c/ec1d77cb0ee9
  - [bpf-next,v3,3/6] bpf: Exit early if reg_bounds_sync gets invalid inputs
    https://git.kernel.org/bpf/bpf-next/c/a2a14e874b4e
  - [bpf-next,v3,4/6] bpf: Simulate branches to prune based on range violations
    https://git.kernel.org/bpf/bpf-next/c/b254c6d816e5
  - [bpf-next,v3,5/6] selftests/bpf: Cover invariant violation case from syzbot
    https://git.kernel.org/bpf/bpf-next/c/2ba199067b89
  - [bpf-next,v3,6/6] selftests/bpf: Remove invariant violation flags
    https://git.kernel.org/bpf/bpf-next/c/7cbded6ed98f

You are awesome, thank you!
-- 
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