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* [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration
@ 2026-05-11 16:21 Paul Chaignon
  2026-05-11 16:22 ` [PATCH 6.6.y 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Paul Chaignon
                   ` (11 more replies)
  0 siblings, 12 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:21 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

The first patch in this patchset was already backported before, as
commit ecc2aeeaa08a, to address CVE-2023-52920 [1]. That backport was
however later reverted in commit 199f04528737 because it reduced the
efficiency of the BPF verifier, to the point that it rejected some
previously-accepted programs.

This patchset backports commit 41f6f64e6999 ("bpf: support non-r10
register spill/fill to/from stack in precision tracking") again, but
this time with the subsequent commits that improved the efficiency of
the verifier. In addition, the last two commits fix and test a
regression that was later found in commit 41f6f64e6999.

It took us a while with Shung-Hsi to come back to this because we felt
we didn't have enough test coverage to backport this. That changed with
the stable BPF CI Shung-Hsi built for v6.6, which successfully
validated this patchset [2]. In addition, I tested the impact of this
patchset on the verifier's efficiency with Cilium's BPF programs [3]:
it significantly improves, reducing the number of instructions the
verifier has to analyze by up to 87% in some cases!

1: https://lore.kernel.org/linux-cve-announce/2024110518-CVE-2023-52920-17f6@gregkh/
2: https://github.com/pchaigno/stable-bpf-ci/actions/runs/25671397661/job/75357317078
3: https://pchaigno.github.io/test-verifier-complexity.html

Andrii Nakryiko (10):
  bpf: support non-r10 register spill/fill to/from stack in precision
    tracking
  selftests/bpf: add stack access precision test
  bpf: preserve STACK_ZERO slots on partial reg spills
  selftests/bpf: validate STACK_ZERO is preserved on subreg spill
  bpf: preserve constant zero when doing partial register restore
  selftests/bpf: validate zero preservation for sub-slot loads
  bpf: track aligned STACK_ZERO cases as imprecise spilled registers
  selftests/bpf: validate precision logic in
    partial_stack_load_preserves_zeros
  bpf: handle fake register spill to stack with BPF_ST_MEM instruction
  selftests/bpf: validate fake register spill/fill precision
    backtracking logic

 include/linux/bpf_verifier.h                  |  31 +-
 kernel/bpf/verifier.c                         | 233 +++++++++------
 .../selftests/bpf/progs/verifier_spill_fill.c | 281 ++++++++++++++++++
 .../bpf/progs/verifier_subprog_precision.c    |  87 +++++-
 .../testing/selftests/bpf/verifier/precise.c  |  38 ++-
 5 files changed, 557 insertions(+), 113 deletions(-)

-- 
2.43.0


^ permalink raw reply	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
@ 2026-05-11 16:22 ` Paul Chaignon
  2026-05-11 16:23 ` [PATCH 6.6.y 02/10] selftests/bpf: add stack access precision test Paul Chaignon
                   ` (10 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:22 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 41f6f64e6999a837048b1bd13a2f8742964eca6b ]

Use instruction (jump) history to record instructions that performed
register spill/fill to/from stack, regardless if this was done through
read-only r10 register, or any other register after copying r10 into it
*and* potentially adjusting offset.

To make this work reliably, we push extra per-instruction flags into
instruction history, encoding stack slot index (spi) and stack frame
number in extra 10 bit flags we take away from prev_idx in instruction
history. We don't touch idx field for maximum performance, as it's
checked most frequently during backtracking.

This change removes basically the last remaining practical limitation of
precision backtracking logic in BPF verifier. It fixes known
deficiencies, but also opens up new opportunities to reduce number of
verified states, explored in the subsequent patches.

There are only three differences in selftests' BPF object files
according to veristat, all in the positive direction (less states).

File                                    Program        Insns (A)  Insns (B)  Insns  (DIFF)  States (A)  States (B)  States (DIFF)
--------------------------------------  -------------  ---------  ---------  -------------  ----------  ----------  -------------
test_cls_redirect_dynptr.bpf.linked3.o  cls_redirect        2987       2864  -123 (-4.12%)         240         231    -9 (-3.75%)
xdp_synproxy_kern.bpf.linked3.o         syncookie_tc       82848      82661  -187 (-0.23%)        5107        5073   -34 (-0.67%)
xdp_synproxy_kern.bpf.linked3.o         syncookie_xdp      85116      84964  -152 (-0.18%)        5162        5130   -32 (-0.62%)

Note, I avoided renaming jmp_history to more generic insn_hist to
minimize number of lines changed and potential merge conflicts between
bpf and bpf-next trees.

Notice also cur_hist_entry pointer reset to NULL at the beginning of
instruction verification loop. This pointer avoids the problem of
relying on last jump history entry's insn_idx to determine whether we
already have entry for current instruction or not. It can happen that we
added jump history entry because current instruction is_jmp_point(), but
also we need to add instruction flags for stack access. In this case, we
don't want to entries, so we need to reuse last added entry, if it is
present.

Relying on insn_idx comparison has the same ambiguity problem as the one
that was fixed recently in [0], so we avoid that.

  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20231110002638.4168352-3-andrii@kernel.org/

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reported-by: Tao Lyu <tao.lyu@epfl.ch>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[ Note: Adapted the expected log format for selftests as the map format
  in verifier logs was changed in commits 1db747d75b1d and
  0c95c9fdb696. ]
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/bpf_verifier.h                  |  31 +++-
 kernel/bpf/verifier.c                         | 175 ++++++++++--------
 .../bpf/progs/verifier_subprog_precision.c    |  23 ++-
 .../testing/selftests/bpf/verifier/precise.c  |  38 ++--
 4 files changed, 169 insertions(+), 98 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 32e89758176b..dba211d3bb9a 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -319,12 +319,34 @@ struct bpf_func_state {
 	struct bpf_stack_state *stack;
 };
 
-struct bpf_idx_pair {
-	u32 prev_idx;
+#define MAX_CALL_FRAMES 8
+
+/* instruction history flags, used in bpf_jmp_history_entry.flags field */
+enum {
+	/* instruction references stack slot through PTR_TO_STACK register;
+	 * we also store stack's frame number in lower 3 bits (MAX_CALL_FRAMES is 8)
+	 * and accessed stack slot's index in next 6 bits (MAX_BPF_STACK is 512,
+	 * 8 bytes per slot, so slot index (spi) is [0, 63])
+	 */
+	INSN_F_FRAMENO_MASK = 0x7, /* 3 bits */
+
+	INSN_F_SPI_MASK = 0x3f, /* 6 bits */
+	INSN_F_SPI_SHIFT = 3, /* shifted 3 bits to the left */
+
+	INSN_F_STACK_ACCESS = BIT(9), /* we need 10 bits total */
+};
+
+static_assert(INSN_F_FRAMENO_MASK + 1 >= MAX_CALL_FRAMES);
+static_assert(INSN_F_SPI_MASK + 1 >= MAX_BPF_STACK / 8);
+
+struct bpf_jmp_history_entry {
 	u32 idx;
+	/* insn idx can't be bigger than 1 million */
+	u32 prev_idx : 22;
+	/* special flags, e.g., whether insn is doing register stack spill/load */
+	u32 flags : 10;
 };
 
-#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)
 struct bpf_verifier_state {
@@ -407,7 +429,7 @@ struct bpf_verifier_state {
 	 * For most states jmp_history_cnt is [0-3].
 	 * For loops can go up to ~40.
 	 */
-	struct bpf_idx_pair *jmp_history;
+	struct bpf_jmp_history_entry *jmp_history;
 	u32 jmp_history_cnt;
 	u32 dfs_depth;
 	u32 callback_unroll_depth;
@@ -641,6 +663,7 @@ struct bpf_verifier_env {
 		int cur_stack;
 	} cfg;
 	struct backtrack_state bt;
+	struct bpf_jmp_history_entry *cur_hist_ent;
 	u32 pass_cnt; /* number of times do_check() was called */
 	u32 subprog_cnt;
 	/* number of instructions analyzed by the verifier */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 45eb795c8c04..e44da369dff6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1763,8 +1763,8 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 	int i, err;
 
 	dst_state->jmp_history = copy_array(dst_state->jmp_history, src->jmp_history,
-					    src->jmp_history_cnt, sizeof(struct bpf_idx_pair),
-					    GFP_USER);
+					  src->jmp_history_cnt, sizeof(*dst_state->jmp_history),
+					  GFP_USER);
 	if (!dst_state->jmp_history)
 		return -ENOMEM;
 	dst_state->jmp_history_cnt = src->jmp_history_cnt;
@@ -3418,6 +3418,21 @@ static int check_reg_arg(struct bpf_verifier_env *env, u32 regno,
 	return __check_reg_arg(env, state->regs, regno, t);
 }
 
+static int insn_stack_access_flags(int frameno, int spi)
+{
+	return INSN_F_STACK_ACCESS | (spi << INSN_F_SPI_SHIFT) | frameno;
+}
+
+static int insn_stack_access_spi(int insn_flags)
+{
+	return (insn_flags >> INSN_F_SPI_SHIFT) & INSN_F_SPI_MASK;
+}
+
+static int insn_stack_access_frameno(int insn_flags)
+{
+	return insn_flags & INSN_F_FRAMENO_MASK;
+}
+
 static void mark_jmp_point(struct bpf_verifier_env *env, int idx)
 {
 	env->insn_aux_data[idx].jmp_point = true;
@@ -3429,28 +3444,51 @@ static bool is_jmp_point(struct bpf_verifier_env *env, int insn_idx)
 }
 
 /* for any branch, call, exit record the history of jmps in the given state */
-static int push_jmp_history(struct bpf_verifier_env *env,
-			    struct bpf_verifier_state *cur)
+static int push_jmp_history(struct bpf_verifier_env *env, struct bpf_verifier_state *cur,
+			    int insn_flags)
 {
 	u32 cnt = cur->jmp_history_cnt;
-	struct bpf_idx_pair *p;
+	struct bpf_jmp_history_entry *p;
 	size_t alloc_size;
 
-	if (!is_jmp_point(env, env->insn_idx))
+	/* combine instruction flags if we already recorded this instruction */
+	if (env->cur_hist_ent) {
+		/* atomic instructions push insn_flags twice, for READ and
+		 * WRITE sides, but they should agree on stack slot
+		 */
+		WARN_ONCE((env->cur_hist_ent->flags & insn_flags) &&
+			  (env->cur_hist_ent->flags & insn_flags) != insn_flags,
+			  "verifier insn history bug: insn_idx %d cur flags %x new flags %x\n",
+			  env->insn_idx, env->cur_hist_ent->flags, insn_flags);
+		env->cur_hist_ent->flags |= insn_flags;
 		return 0;
+	}
 
 	cnt++;
 	alloc_size = kmalloc_size_roundup(size_mul(cnt, sizeof(*p)));
 	p = krealloc(cur->jmp_history, alloc_size, GFP_USER);
 	if (!p)
 		return -ENOMEM;
-	p[cnt - 1].idx = env->insn_idx;
-	p[cnt - 1].prev_idx = env->prev_insn_idx;
 	cur->jmp_history = p;
+
+	p = &cur->jmp_history[cnt - 1];
+	p->idx = env->insn_idx;
+	p->prev_idx = env->prev_insn_idx;
+	p->flags = insn_flags;
 	cur->jmp_history_cnt = cnt;
+	env->cur_hist_ent = p;
+
 	return 0;
 }
 
+static struct bpf_jmp_history_entry *get_jmp_hist_entry(struct bpf_verifier_state *st,
+						        u32 hist_end, int insn_idx)
+{
+	if (hist_end > 0 && st->jmp_history[hist_end - 1].idx == insn_idx)
+		return &st->jmp_history[hist_end - 1];
+	return NULL;
+}
+
 /* Backtrack one insn at a time. If idx is not at the top of recorded
  * history then previous instruction came from straight line execution.
  * Return -ENOENT if we exhausted all instructions within given state.
@@ -3612,9 +3650,14 @@ static inline bool bt_is_reg_set(struct backtrack_state *bt, u32 reg)
 	return bt->reg_masks[bt->frame] & (1 << reg);
 }
 
+static inline bool bt_is_frame_slot_set(struct backtrack_state *bt, u32 frame, u32 slot)
+{
+	return bt->stack_masks[frame] & (1ull << slot);
+}
+
 static inline bool bt_is_slot_set(struct backtrack_state *bt, u32 slot)
 {
-	return bt->stack_masks[bt->frame] & (1ull << slot);
+	return bt_is_frame_slot_set(bt, bt->frame, slot);
 }
 
 /* format registers bitmask, e.g., "r0,r2,r4" for 0x15 mask */
@@ -3668,7 +3711,7 @@ static bool calls_callback(struct bpf_verifier_env *env, int insn_idx);
  *   - *was* processed previously during backtracking.
  */
 static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
-			  struct backtrack_state *bt)
+			  struct bpf_jmp_history_entry *hist, struct backtrack_state *bt)
 {
 	const struct bpf_insn_cbs cbs = {
 		.cb_call	= disasm_kfunc_name,
@@ -3681,7 +3724,7 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
 	u8 mode = BPF_MODE(insn->code);
 	u32 dreg = insn->dst_reg;
 	u32 sreg = insn->src_reg;
-	u32 spi, i;
+	u32 spi, i, fr;
 
 	if (insn->code == 0)
 		return 0;
@@ -3744,20 +3787,15 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
 		 * by 'precise' mark in corresponding register of this state.
 		 * No further tracking necessary.
 		 */
-		if (insn->src_reg != BPF_REG_FP)
+		if (!hist || !(hist->flags & INSN_F_STACK_ACCESS))
 			return 0;
-
 		/* dreg = *(u64 *)[fp - off] was a fill from the stack.
 		 * that [fp - off] slot contains scalar that needs to be
 		 * tracked with precision
 		 */
-		spi = (-insn->off - 1) / BPF_REG_SIZE;
-		if (spi >= 64) {
-			verbose(env, "BUG spi %d\n", spi);
-			WARN_ONCE(1, "verifier backtracking bug");
-			return -EFAULT;
-		}
-		bt_set_slot(bt, spi);
+		spi = insn_stack_access_spi(hist->flags);
+		fr = insn_stack_access_frameno(hist->flags);
+		bt_set_frame_slot(bt, fr, spi);
 	} else if (class == BPF_STX || class == BPF_ST) {
 		if (bt_is_reg_set(bt, dreg))
 			/* stx & st shouldn't be using _scalar_ dst_reg
@@ -3766,17 +3804,13 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
 			 */
 			return -ENOTSUPP;
 		/* scalars can only be spilled into stack */
-		if (insn->dst_reg != BPF_REG_FP)
+		if (!hist || !(hist->flags & INSN_F_STACK_ACCESS))
 			return 0;
-		spi = (-insn->off - 1) / BPF_REG_SIZE;
-		if (spi >= 64) {
-			verbose(env, "BUG spi %d\n", spi);
-			WARN_ONCE(1, "verifier backtracking bug");
-			return -EFAULT;
-		}
-		if (!bt_is_slot_set(bt, spi))
+		spi = insn_stack_access_spi(hist->flags);
+		fr = insn_stack_access_frameno(hist->flags);
+		if (!bt_is_frame_slot_set(bt, fr, spi))
 			return 0;
-		bt_clear_slot(bt, spi);
+		bt_clear_frame_slot(bt, fr, spi);
 		if (class == BPF_STX)
 			bt_set_reg(bt, sreg);
 	} else if (class == BPF_JMP || class == BPF_JMP32) {
@@ -3820,10 +3854,14 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
 					WARN_ONCE(1, "verifier backtracking bug");
 					return -EFAULT;
 				}
-				/* we don't track register spills perfectly,
-				 * so fallback to force-precise instead of failing */
-				if (bt_stack_mask(bt) != 0)
-					return -ENOTSUPP;
+				/* we are now tracking register spills correctly,
+				 * so any instance of leftover slots is a bug
+				 */
+				if (bt_stack_mask(bt) != 0) {
+					verbose(env, "BUG stack slots %llx\n", bt_stack_mask(bt));
+					WARN_ONCE(1, "verifier backtracking bug (subprog leftover stack slots)");
+					return -EFAULT;
+				}
 				/* propagate r1-r5 to the caller */
 				for (i = BPF_REG_1; i <= BPF_REG_5; i++) {
 					if (bt_is_reg_set(bt, i)) {
@@ -3848,8 +3886,11 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
 				WARN_ONCE(1, "verifier backtracking bug");
 				return -EFAULT;
 			}
-			if (bt_stack_mask(bt) != 0)
-				return -ENOTSUPP;
+			if (bt_stack_mask(bt) != 0) {
+				verbose(env, "BUG stack slots %llx\n", bt_stack_mask(bt));
+				WARN_ONCE(1, "verifier backtracking bug (callback leftover stack slots)");
+				return -EFAULT;
+			}
 			/* clear r1-r5 in callback subprog's mask */
 			for (i = BPF_REG_1; i <= BPF_REG_5; i++)
 				bt_clear_reg(bt, i);
@@ -4286,6 +4327,7 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
 	for (;;) {
 		DECLARE_BITMAP(mask, 64);
 		u32 history = st->jmp_history_cnt;
+		struct bpf_jmp_history_entry *hist;
 
 		if (env->log.level & BPF_LOG_LEVEL2) {
 			verbose(env, "mark_precise: frame%d: last_idx %d first_idx %d subseq_idx %d \n",
@@ -4349,7 +4391,8 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
 				err = 0;
 				skip_first = false;
 			} else {
-				err = backtrack_insn(env, i, subseq_idx, bt);
+				hist = get_jmp_hist_entry(st, history, i);
+				err = backtrack_insn(env, i, subseq_idx, hist, bt);
 			}
 			if (err == -ENOTSUPP) {
 				mark_all_scalars_precise(env, env->cur_state);
@@ -4402,22 +4445,10 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
 			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) {
-					/* the sequence of instructions:
-					 * 2: (bf) r3 = r10
-					 * 3: (7b) *(u64 *)(r3 -8) = r0
-					 * 4: (79) r4 = *(u64 *)(r10 -8)
-					 * doesn't contain jmps. It's backtracked
-					 * as a single block.
-					 * During backtracking insn 3 is not recognized as
-					 * stack access, so at the end of backtracking
-					 * stack slot fp-8 is still marked in stack_mask.
-					 * However the parent state may not have accessed
-					 * fp-8 and it's "unallocated" stack space.
-					 * In such case fallback to conservative.
-					 */
-					mark_all_scalars_precise(env, env->cur_state);
-					bt_reset(bt);
-					return 0;
+					verbose(env, "BUG backtracking (stack slot %d, total slots %d)\n",
+						i, func->allocated_stack / BPF_REG_SIZE);
+					WARN_ONCE(1, "verifier backtracking bug (stack slot out of bounds)");
+					return -EFAULT;
 				}
 
 				if (!is_spilled_scalar_reg(&func->stack[i])) {
@@ -4582,7 +4613,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 	int i, slot = -off - 1, spi = slot / BPF_REG_SIZE, err;
 	struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
 	struct bpf_reg_state *reg = NULL;
-	u32 dst_reg = insn->dst_reg;
+	int insn_flags = insn_stack_access_flags(state->frameno, spi);
 
 	/* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0,
 	 * so it's aligned access and [off, off + size) are within stack limits
@@ -4621,17 +4652,6 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 	mark_stack_slot_scratched(env, spi);
 	if (reg && !(off % 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
-			 * stack slot address like [fp - 8]. Other spill of
-			 * scalar via different register has to be conservative.
-			 * Backtrack from here and mark all registers as precise
-			 * that contributed into 'reg' being a constant.
-			 */
-			err = mark_chain_precision(env, value_regno);
-			if (err)
-				return err;
-		}
 		save_register_state(state, spi, reg, size);
 		/* Break the relation on a narrowing spill. */
 		if (fls64(reg->umax_value) > BITS_PER_BYTE * size)
@@ -4643,6 +4663,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		__mark_reg_known(&fake_reg, insn->imm);
 		fake_reg.type = SCALAR_VALUE;
 		save_register_state(state, spi, &fake_reg, size);
+		insn_flags = 0; /* not a register spill */
 	} else if (reg && is_spillable_regtype(reg->type)) {
 		/* register containing pointer is being spilled into stack */
 		if (size != BPF_REG_SIZE) {
@@ -4688,9 +4709,12 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 
 		/* Mark slots affected by this stack write. */
 		for (i = 0; i < size; i++)
-			state->stack[spi].slot_type[(slot - i) % BPF_REG_SIZE] =
-				type;
+			state->stack[spi].slot_type[(slot - i) % BPF_REG_SIZE] = type;
+		insn_flags = 0; /* not a register spill */
 	}
+
+	if (insn_flags)
+		return push_jmp_history(env, env->cur_state, insn_flags);
 	return 0;
 }
 
@@ -4879,6 +4903,7 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 	int i, slot = -off - 1, spi = slot / BPF_REG_SIZE;
 	struct bpf_reg_state *reg;
 	u8 *stype, type;
+	int insn_flags = insn_stack_access_flags(reg_state->frameno, spi);
 
 	stype = reg_state->stack[spi].slot_type;
 	reg = &reg_state->stack[spi].spilled_ptr;
@@ -4924,12 +4949,10 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 					return -EACCES;
 				}
 				mark_reg_unknown(env, state->regs, dst_regno);
+				insn_flags = 0; /* not restoring original register state */
 			}
 			state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
-			return 0;
-		}
-
-		if (dst_regno >= 0) {
+		} else if (dst_regno >= 0) {
 			/* restore register state from stack */
 			copy_register_state(&state->regs[dst_regno], reg);
 			/* mark reg as written since spilled pointer state likely
@@ -4965,7 +4988,10 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 		mark_reg_read(env, reg, reg->parent, REG_LIVE_READ64);
 		if (dst_regno >= 0)
 			mark_reg_stack_read(env, reg_state, off, off + size, dst_regno);
+		insn_flags = 0; /* we are not restoring spilled register */
 	}
+	if (insn_flags)
+		return push_jmp_history(env, env->cur_state, insn_flags);
 	return 0;
 }
 
@@ -7050,7 +7076,6 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 			       BPF_SIZE(insn->code), BPF_WRITE, -1, true, false);
 	if (err)
 		return err;
-
 	return 0;
 }
 
@@ -16845,7 +16870,8 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			 * the precision needs to be propagated back in
 			 * the current state.
 			 */
-			err = err ? : push_jmp_history(env, cur);
+			if (is_jmp_point(env, env->insn_idx))
+				err = err ? : push_jmp_history(env, cur, 0);
 			err = err ? : propagate_precision(env, &sl->state);
 			if (err)
 				return err;
@@ -17069,6 +17095,9 @@ static int do_check(struct bpf_verifier_env *env)
 		u8 class;
 		int err;
 
+		/* reset current history entry on each new instruction */
+		env->cur_hist_ent = NULL;
+
 		env->prev_insn_idx = prev_insn_idx;
 		if (env->insn_idx >= insn_cnt) {
 			verbose(env, "invalid insn idx %d insn_cnt %d\n",
@@ -17108,7 +17137,7 @@ static int do_check(struct bpf_verifier_env *env)
 		}
 
 		if (is_jmp_point(env, env->insn_idx)) {
-			err = push_jmp_history(env, state);
+			err = push_jmp_history(env, state, 0);
 			if (err)
 				return err;
 		}
diff --git a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
index f61d623b1ce8..7c159b561862 100644
--- a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
+++ b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
@@ -541,11 +541,24 @@ static __u64 subprog_spill_reg_precise(void)
 
 SEC("?raw_tp")
 __success __log_level(2)
-/* precision backtracking can't currently handle stack access not through r10,
- * so we won't be able to mark stack slot fp-8 as precise, and so will
- * fallback to forcing all as precise
- */
-__msg("mark_precise: frame0: falling back to forcing all scalars precise")
+__msg("10: (0f) r1 += r7")
+__msg("mark_precise: frame0: last_idx 10 first_idx 7 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r7 stack= before 9: (bf) r1 = r8")
+__msg("mark_precise: frame0: regs=r7 stack= before 8: (27) r7 *= 4")
+__msg("mark_precise: frame0: regs=r7 stack= before 7: (79) r7 = *(u64 *)(r10 -8)")
+__msg("mark_precise: frame0: parent state regs= stack=-8:  R0_w=2 R6_w=1 R8_rw=map_value(off=0,ks=4,vs=16,imm=0) R10=fp0 fp-8_rw=P1")
+__msg("mark_precise: frame0: last_idx 18 first_idx 0 subseq_idx 7")
+__msg("mark_precise: frame0: regs= stack=-8 before 18: (95) exit")
+__msg("mark_precise: frame1: regs= stack= before 17: (0f) r0 += r2")
+__msg("mark_precise: frame1: regs= stack= before 16: (79) r2 = *(u64 *)(r1 +0)")
+__msg("mark_precise: frame1: regs= stack= before 15: (79) r0 = *(u64 *)(r10 -16)")
+__msg("mark_precise: frame1: regs= stack= before 14: (7b) *(u64 *)(r10 -16) = r2")
+__msg("mark_precise: frame1: regs= stack= before 13: (7b) *(u64 *)(r1 +0) = r2")
+__msg("mark_precise: frame1: regs=r2 stack= before 6: (85) call pc+6")
+__msg("mark_precise: frame0: regs=r2 stack= before 5: (bf) r2 = r6")
+__msg("mark_precise: frame0: regs=r6 stack= before 4: (07) r1 += -8")
+__msg("mark_precise: frame0: regs=r6 stack= before 3: (bf) r1 = r10")
+__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 1")
 __naked int subprog_spill_into_parent_stack_slot_precise(void)
 {
 	asm volatile (
diff --git a/tools/testing/selftests/bpf/verifier/precise.c b/tools/testing/selftests/bpf/verifier/precise.c
index 0d84dd1f38b6..8a2ff81d8350 100644
--- a/tools/testing/selftests/bpf/verifier/precise.c
+++ b/tools/testing/selftests/bpf/verifier/precise.c
@@ -140,10 +140,11 @@
 	.result = REJECT,
 },
 {
-	"precise: ST insn causing spi > allocated_stack",
+	"precise: ST zero to stack insn is supported",
 	.insns = {
 	BPF_MOV64_REG(BPF_REG_3, BPF_REG_10),
 	BPF_JMP_IMM(BPF_JNE, BPF_REG_3, 123, 0),
+	/* not a register spill, so we stop precision propagation for R4 here */
 	BPF_ST_MEM(BPF_DW, BPF_REG_3, -8, 0),
 	BPF_LDX_MEM(BPF_DW, BPF_REG_4, BPF_REG_10, -8),
 	BPF_MOV64_IMM(BPF_REG_0, -1),
@@ -157,11 +158,11 @@
 	mark_precise: frame0: last_idx 4 first_idx 2\
 	mark_precise: frame0: regs=r4 stack= before 4\
 	mark_precise: frame0: regs=r4 stack= before 3\
-	mark_precise: frame0: regs= stack=-8 before 2\
-	mark_precise: frame0: falling back to forcing all scalars precise\
-	force_precise: frame0: forcing r0 to be precise\
 	mark_precise: frame0: last_idx 5 first_idx 5\
-	mark_precise: frame0: parent state regs= stack=:",
+	mark_precise: frame0: parent state regs=r0 stack=:\
+	mark_precise: frame0: last_idx 4 first_idx 2\
+	mark_precise: frame0: regs=r0 stack= before 4\
+	5: R0=-1 R4=0",
 	.result = VERBOSE_ACCEPT,
 	.retval = -1,
 },
@@ -169,6 +170,8 @@
 	"precise: STX insn causing spi > allocated_stack",
 	.insns = {
 	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_prandom_u32),
+	/* make later reg spill more interesting by having somewhat known scalar */
+	BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xff),
 	BPF_MOV64_REG(BPF_REG_3, BPF_REG_10),
 	BPF_JMP_IMM(BPF_JNE, BPF_REG_3, 123, 0),
 	BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, -8),
@@ -179,18 +182,21 @@
 	},
 	.prog_type = BPF_PROG_TYPE_XDP,
 	.flags = BPF_F_TEST_STATE_FREQ,
-	.errstr = "mark_precise: frame0: last_idx 6 first_idx 6\
+	.errstr = "mark_precise: frame0: last_idx 7 first_idx 7\
 	mark_precise: frame0: parent state regs=r4 stack=:\
-	mark_precise: frame0: last_idx 5 first_idx 3\
-	mark_precise: frame0: regs=r4 stack= before 5\
-	mark_precise: frame0: regs=r4 stack= before 4\
-	mark_precise: frame0: regs= stack=-8 before 3\
-	mark_precise: frame0: falling back to forcing all scalars precise\
-	force_precise: frame0: forcing r0 to be precise\
-	force_precise: frame0: forcing r0 to be precise\
-	force_precise: frame0: forcing r0 to be precise\
-	force_precise: frame0: forcing r0 to be precise\
-	mark_precise: frame0: last_idx 6 first_idx 6\
+	mark_precise: frame0: last_idx 6 first_idx 4\
+	mark_precise: frame0: regs=r4 stack= before 6: (b7) r0 = -1\
+	mark_precise: frame0: regs=r4 stack= before 5: (79) r4 = *(u64 *)(r10 -8)\
+	mark_precise: frame0: regs= stack=-8 before 4: (7b) *(u64 *)(r3 -8) = r0\
+	mark_precise: frame0: parent state regs=r0 stack=:\
+	mark_precise: frame0: last_idx 3 first_idx 3\
+	mark_precise: frame0: regs=r0 stack= before 3: (55) if r3 != 0x7b goto pc+0\
+	mark_precise: frame0: regs=r0 stack= before 2: (bf) r3 = r10\
+	mark_precise: frame0: regs=r0 stack= before 1: (57) r0 &= 255\
+	mark_precise: frame0: parent state regs=r0 stack=:\
+	mark_precise: frame0: last_idx 0 first_idx 0\
+	mark_precise: frame0: regs=r0 stack= before 0: (85) call bpf_get_prandom_u32#7\
+	mark_precise: frame0: last_idx 7 first_idx 7\
 	mark_precise: frame0: parent state regs= stack=:",
 	.result = VERBOSE_ACCEPT,
 	.retval = -1,
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 02/10] selftests/bpf: add stack access precision test
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
  2026-05-11 16:22 ` [PATCH 6.6.y 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Paul Chaignon
@ 2026-05-11 16:23 ` Paul Chaignon
  2026-05-11 16:23 ` [PATCH 6.6.y 03/10] bpf: preserve STACK_ZERO slots on partial reg spills Paul Chaignon
                   ` (9 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:23 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 876301881c436bf38e83a2c0d276a24b642e4aab ]

Add a new selftests that validates precision tracking for stack access
instruction, using both r10-based and non-r10-based accesses. For
non-r10 ones we also make sure to have non-zero var_off to validate that
final stack offset is tracked properly in instruction history
information inside verifier.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../bpf/progs/verifier_subprog_precision.c    | 64 +++++++++++++++++--
 1 file changed, 59 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
index 7c159b561862..4b8b0f45d17d 100644
--- a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
+++ b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
@@ -593,14 +593,68 @@ __naked int subprog_spill_into_parent_stack_slot_precise(void)
 	);
 }
 
-__naked __noinline __used
-static __u64 subprog_with_checkpoint(void)
+SEC("?raw_tp")
+__success __log_level(2)
+__msg("17: (0f) r1 += r0")
+__msg("mark_precise: frame0: last_idx 17 first_idx 0 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r0 stack= before 16: (bf) r1 = r7")
+__msg("mark_precise: frame0: regs=r0 stack= before 15: (27) r0 *= 4")
+__msg("mark_precise: frame0: regs=r0 stack= before 14: (79) r0 = *(u64 *)(r10 -16)")
+__msg("mark_precise: frame0: regs= stack=-16 before 13: (7b) *(u64 *)(r7 -8) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 12: (79) r0 = *(u64 *)(r8 +16)")
+__msg("mark_precise: frame0: regs= stack=-16 before 11: (7b) *(u64 *)(r8 +16) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 10: (79) r0 = *(u64 *)(r7 -8)")
+__msg("mark_precise: frame0: regs= stack=-16 before 9: (7b) *(u64 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 8: (07) r8 += -32")
+__msg("mark_precise: frame0: regs=r0 stack= before 7: (bf) r8 = r10")
+__msg("mark_precise: frame0: regs=r0 stack= before 6: (07) r7 += -8")
+__msg("mark_precise: frame0: regs=r0 stack= before 5: (bf) r7 = r10")
+__msg("mark_precise: frame0: regs=r0 stack= before 21: (95) exit")
+__msg("mark_precise: frame1: regs=r0 stack= before 20: (bf) r0 = r1")
+__msg("mark_precise: frame1: regs=r1 stack= before 4: (85) call pc+15")
+__msg("mark_precise: frame0: regs=r1 stack= before 3: (bf) r1 = r6")
+__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 1")
+__naked int stack_slot_aliases_precision(void)
 {
 	asm volatile (
-		"r0 = 0;"
-		/* guaranteed checkpoint if BPF_F_TEST_STATE_FREQ is used */
-		"goto +0;"
+		"r6 = 1;"
+		/* pass r6 through r1 into subprog to get it back as r0;
+		 * this whole chain will have to be marked as precise later
+		 */
+		"r1 = r6;"
+		"call identity_subprog;"
+		/* let's setup two registers that are aliased to r10 */
+		"r7 = r10;"
+		"r7 += -8;"			/* r7 = r10 - 8 */
+		"r8 = r10;"
+		"r8 += -32;"			/* r8 = r10 - 32 */
+		/* now spill subprog's return value (a r6 -> r1 -> r0 chain)
+		 * a few times through different stack pointer regs, making
+		 * sure to use r10, r7, and r8 both in LDX and STX insns, and
+		 * *importantly* also using a combination of const var_off and
+		 * insn->off to validate that we record final stack slot
+		 * correctly, instead of relying on just insn->off derivation,
+		 * which is only valid for r10-based stack offset
+		 */
+		"*(u64 *)(r10 - 16) = r0;"
+		"r0 = *(u64 *)(r7 - 8);"	/* r7 - 8 == r10 - 16 */
+		"*(u64 *)(r8 + 16) = r0;"	/* r8 + 16 = r10 - 16 */
+		"r0 = *(u64 *)(r8 + 16);"
+		"*(u64 *)(r7 - 8) = r0;"
+		"r0 = *(u64 *)(r10 - 16);"
+		/* get ready to use r0 as an index into array to force precision */
+		"r0 *= 4;"
+		"r1 = %[vals];"
+		/* here r0->r1->r6 chain is forced to be precise and has to be
+		 * propagated back to the beginning, including through the
+		 * subprog call and all the stack spills and loads
+		 */
+		"r1 += r0;"
+		"r0 = *(u32 *)(r1 + 0);"
 		"exit;"
+		:
+		: __imm_ptr(vals)
+		: __clobber_common, "r6"
 	);
 }
 
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 03/10] bpf: preserve STACK_ZERO slots on partial reg spills
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
  2026-05-11 16:22 ` [PATCH 6.6.y 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Paul Chaignon
  2026-05-11 16:23 ` [PATCH 6.6.y 02/10] selftests/bpf: add stack access precision test Paul Chaignon
@ 2026-05-11 16:23 ` Paul Chaignon
  2026-05-11 16:24 ` [PATCH 6.6.y 04/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill Paul Chaignon
                   ` (8 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:23 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit eaf18febd6ebc381aeb61543705148b3e28c7c47 ]

Instead of always forcing STACK_ZERO slots to STACK_MISC, preserve it in
situations where this is possible. E.g., when spilling register as
1/2/4-byte subslots on the stack, all the remaining bytes in the stack
slot do not automatically become unknown. If we knew they contained
zeroes, we can preserve those STACK_ZERO markers.

Add a helper mark_stack_slot_misc(), similar to scrub_spilled_slot(),
but that doesn't overwrite either STACK_INVALID nor STACK_ZERO. Note
that we need to take into account possibility of being in unprivileged
mode, in which case STACK_INVALID is forced to STACK_MISC for correctness,
as treating STACK_INVALID as equivalent STACK_MISC is only enabled in
privileged mode.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-5-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e44da369dff6..8309504d1660 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1347,6 +1347,21 @@ static bool is_spilled_scalar_reg(const struct bpf_stack_state *stack)
 	       stack->spilled_ptr.type == SCALAR_VALUE;
 }
 
+/* Mark stack slot as STACK_MISC, unless it is already STACK_INVALID, in which
+ * case they are equivalent, or it's STACK_ZERO, in which case we preserve
+ * more precise STACK_ZERO.
+ * Note, in uprivileged mode leaving STACK_INVALID is wrong, so we take
+ * env->allow_ptr_leaks into account and force STACK_MISC, if necessary.
+ */
+static void mark_stack_slot_misc(struct bpf_verifier_env *env, u8 *stype)
+{
+	if (*stype == STACK_ZERO)
+		return;
+	if (env->allow_ptr_leaks && *stype == STACK_INVALID)
+		return;
+	*stype = STACK_MISC;
+}
+
 static void scrub_spilled_slot(u8 *stype)
 {
 	if (*stype != STACK_INVALID)
@@ -4577,7 +4592,8 @@ static void copy_register_state(struct bpf_reg_state *dst, const struct bpf_reg_
 	dst->live = live;
 }
 
-static void save_register_state(struct bpf_func_state *state,
+static void save_register_state(struct bpf_verifier_env *env,
+				struct bpf_func_state *state,
 				int spi, struct bpf_reg_state *reg,
 				int size)
 {
@@ -4592,7 +4608,7 @@ static void save_register_state(struct bpf_func_state *state,
 
 	/* size < 8 bytes spill */
 	for (; i; i--)
-		scrub_spilled_slot(&state->stack[spi].slot_type[i - 1]);
+		mark_stack_slot_misc(env, &state->stack[spi].slot_type[i - 1]);
 }
 
 static bool is_bpf_st_mem(struct bpf_insn *insn)
@@ -4652,7 +4668,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 	mark_stack_slot_scratched(env, spi);
 	if (reg && !(off % BPF_REG_SIZE) && register_is_bounded(reg) &&
 	    !register_is_null(reg) && env->bpf_capable) {
-		save_register_state(state, spi, reg, size);
+		save_register_state(env, state, spi, reg, size);
 		/* Break the relation on a narrowing spill. */
 		if (fls64(reg->umax_value) > BITS_PER_BYTE * size)
 			state->stack[spi].spilled_ptr.id = 0;
@@ -4662,7 +4678,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 
 		__mark_reg_known(&fake_reg, insn->imm);
 		fake_reg.type = SCALAR_VALUE;
-		save_register_state(state, spi, &fake_reg, size);
+		save_register_state(env, state, spi, &fake_reg, size);
 		insn_flags = 0; /* not a register spill */
 	} else if (reg && is_spillable_regtype(reg->type)) {
 		/* register containing pointer is being spilled into stack */
@@ -4675,7 +4691,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 			verbose(env, "cannot spill pointers to stack into stack frame of the caller\n");
 			return -EINVAL;
 		}
-		save_register_state(state, spi, reg, size);
+		save_register_state(env, state, spi, reg, size);
 	} else {
 		u8 type = STACK_MISC;
 
@@ -4942,6 +4958,8 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 						continue;
 					if (type == STACK_MISC)
 						continue;
+					if (type == STACK_ZERO)
+						continue;
 					if (type == STACK_INVALID && env->allow_uninit_stack)
 						continue;
 					verbose(env, "invalid read from stack off %d+%d size %d\n",
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 04/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (2 preceding siblings ...)
  2026-05-11 16:23 ` [PATCH 6.6.y 03/10] bpf: preserve STACK_ZERO slots on partial reg spills Paul Chaignon
@ 2026-05-11 16:24 ` Paul Chaignon
  2026-05-11 16:24 ` [PATCH 6.6.y 05/10] bpf: preserve constant zero when doing partial register restore Paul Chaignon
                   ` (7 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:24 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit b33ceb6a3d2ee07fdd836373383a6d4783581324 ]

Add tests validating that STACK_ZERO slots are preserved when slot is
partially overwritten with subregister spill.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-6-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_spill_fill.c | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index 6115520154e3..d9dabae81176 100644
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -4,6 +4,7 @@
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
+#include <../../../tools/include/linux/filter.h>
 
 struct {
 	__uint(type, BPF_MAP_TYPE_RINGBUF);
@@ -450,4 +451,43 @@ l0_%=:	r1 >>= 16;					\
 	: __clobber_all);
 }
 
+SEC("raw_tp")
+__log_level(2)
+__success
+__msg("fp-8=0m??mmmm")
+__msg("fp-16=00mm??mm")
+__msg("fp-24=00mm???m")
+__naked void spill_subregs_preserve_stack_zero(void)
+{
+	asm volatile (
+		"call %[bpf_get_prandom_u32];"
+
+		/* 32-bit subreg spill with ZERO, MISC, and INVALID */
+		".8byte %[fp1_u8_st_zero];"   /* ZERO, LLVM-18+: *(u8 *)(r10 -1) = 0; */
+		"*(u8 *)(r10 -2) = r0;"       /* MISC */
+		/* fp-3 and fp-4 stay INVALID */
+		"*(u32 *)(r10 -8) = r0;"
+
+		/* 16-bit subreg spill with ZERO, MISC, and INVALID */
+		".8byte %[fp10_u16_st_zero];" /* ZERO, LLVM-18+: *(u16 *)(r10 -10) = 0; */
+		"*(u16 *)(r10 -12) = r0;"     /* MISC */
+		/* fp-13 and fp-14 stay INVALID */
+		"*(u16 *)(r10 -16) = r0;"
+
+		/* 8-bit subreg spill with ZERO, MISC, and INVALID */
+		".8byte %[fp18_u16_st_zero];" /* ZERO, LLVM-18+: *(u16 *)(r18 -10) = 0; */
+		"*(u16 *)(r10 -20) = r0;"     /* MISC */
+		/* fp-21, fp-22, and fp-23 stay INVALID */
+		"*(u8 *)(r10 -24) = r0;"
+
+		"r0 = 0;"
+		"exit;"
+	:
+	: __imm(bpf_get_prandom_u32),
+	  __imm_insn(fp1_u8_st_zero, BPF_ST_MEM(BPF_B, BPF_REG_FP, -1, 0)),
+	  __imm_insn(fp10_u16_st_zero, BPF_ST_MEM(BPF_H, BPF_REG_FP, -10, 0)),
+	  __imm_insn(fp18_u16_st_zero, BPF_ST_MEM(BPF_H, BPF_REG_FP, -18, 0))
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 05/10] bpf: preserve constant zero when doing partial register restore
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (3 preceding siblings ...)
  2026-05-11 16:24 ` [PATCH 6.6.y 04/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill Paul Chaignon
@ 2026-05-11 16:24 ` Paul Chaignon
  2026-05-11 16:24 ` [PATCH 6.6.y 06/10] selftests/bpf: validate zero preservation for sub-slot loads Paul Chaignon
                   ` (6 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:24 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit e322f0bcb8d371f4606eaf141c7f967e1a79bcb7 ]

Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from
stack from slot that has register spilled into it and that register has
a constant value zero, preserve that zero and mark spilled register as
precise for that. This makes spilled const zero register and STACK_ZERO
cases equivalent in their behavior.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-7-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8309504d1660..eaeb996ff56a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4952,22 +4952,39 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
 				copy_register_state(&state->regs[dst_regno], reg);
 				state->regs[dst_regno].subreg_def = subreg_def;
 			} else {
+				int spill_cnt = 0, zero_cnt = 0;
+
 				for (i = 0; i < size; i++) {
 					type = stype[(slot - i) % BPF_REG_SIZE];
-					if (type == STACK_SPILL)
+					if (type == STACK_SPILL) {
+						spill_cnt++;
 						continue;
+					}
 					if (type == STACK_MISC)
 						continue;
-					if (type == STACK_ZERO)
+					if (type == STACK_ZERO) {
+						zero_cnt++;
 						continue;
+					}
 					if (type == STACK_INVALID && env->allow_uninit_stack)
 						continue;
 					verbose(env, "invalid read from stack off %d+%d size %d\n",
 						off, i, size);
 					return -EACCES;
 				}
-				mark_reg_unknown(env, state->regs, dst_regno);
-				insn_flags = 0; /* not restoring original register state */
+
+				if (spill_cnt == size &&
+				    tnum_is_const(reg->var_off) && reg->var_off.value == 0) {
+					__mark_reg_const_zero(&state->regs[dst_regno]);
+					/* this IS register fill, so keep insn_flags */
+				} else if (zero_cnt == size) {
+					/* similarly to mark_reg_stack_read(), preserve zeroes */
+					__mark_reg_const_zero(&state->regs[dst_regno]);
+					insn_flags = 0; /* not restoring original register state */
+				} else {
+					mark_reg_unknown(env, state->regs, dst_regno);
+					insn_flags = 0; /* not restoring original register state */
+				}
 			}
 			state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
 		} else if (dst_regno >= 0) {
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 06/10] selftests/bpf: validate zero preservation for sub-slot loads
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (4 preceding siblings ...)
  2026-05-11 16:24 ` [PATCH 6.6.y 05/10] bpf: preserve constant zero when doing partial register restore Paul Chaignon
@ 2026-05-11 16:24 ` Paul Chaignon
  2026-05-11 16:24 ` [PATCH 6.6.y 07/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Paul Chaignon
                   ` (5 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:24 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit add1cd7f22e61756987865ada9fe95cd86569025 ]

Validate that 1-, 2-, and 4-byte loads from stack slots not aligned on
8-byte boundary still preserve zero, when loading from all-STACK_ZERO
sub-slots, or when stack sub-slots are covered by spilled register with
known constant zero value.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-8-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_spill_fill.c | 71 +++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index d9dabae81176..41fd61299eab 100644
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -490,4 +490,75 @@ __naked void spill_subregs_preserve_stack_zero(void)
 	: __clobber_all);
 }
 
+char single_byte_buf[1] SEC(".data.single_byte_buf");
+
+SEC("raw_tp")
+__log_level(2)
+__success
+__naked void partial_stack_load_preserves_zeros(void)
+{
+	asm volatile (
+		/* fp-8 is all STACK_ZERO */
+		".8byte %[fp8_st_zero];" /* LLVM-18+: *(u64 *)(r10 -8) = 0; */
+
+		/* fp-16 is const zero register */
+		"r0 = 0;"
+		"*(u64 *)(r10 -16) = r0;"
+
+		/* load single U8 from non-aligned STACK_ZERO slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u8 *)(r10 -1);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U8 from non-aligned ZERO REG slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u8 *)(r10 -9);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U16 from non-aligned STACK_ZERO slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u16 *)(r10 -2);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U16 from non-aligned ZERO REG slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u16 *)(r10 -10);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U32 from non-aligned STACK_ZERO slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u32 *)(r10 -4);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U32 from non-aligned ZERO REG slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u32 *)(r10 -12);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* for completeness, load U64 from STACK_ZERO slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u64 *)(r10 -8);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* for completeness, load U64 from ZERO REG slot */
+		"r1 = %[single_byte_buf];"
+		"r2 = *(u64 *)(r10 -16);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		"r0 = 0;"
+		"exit;"
+	:
+	: __imm_ptr(single_byte_buf),
+	  __imm_insn(fp8_st_zero, BPF_ST_MEM(BPF_DW, BPF_REG_FP, -8, 0))
+	: __clobber_common);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 07/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (5 preceding siblings ...)
  2026-05-11 16:24 ` [PATCH 6.6.y 06/10] selftests/bpf: validate zero preservation for sub-slot loads Paul Chaignon
@ 2026-05-11 16:24 ` Paul Chaignon
  2026-05-11 16:24 ` [PATCH 6.6.y 08/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros Paul Chaignon
                   ` (4 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:24 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 18a433b62061e3d787bfc3e670fa711fecbd7cb4 ]

Now that precision backtracing is supporting register spill/fill to/from
stack, there is another oportunity to be exploited here: minimizing
precise STACK_ZERO cases. With a simple code change we can rely on
initially imprecise register spill tracking for cases when register
spilled to stack was a known zero.

This is a very common case for initializing on the stack variables,
including rather large structures. Often times zero has no special
meaning for the subsequent BPF program logic and is often overwritten
with non-zero values soon afterwards. But due to STACK_ZERO vs
STACK_MISC tracking, such initial zero initialization actually causes
duplication of verifier states as STACK_ZERO is clearly different than
STACK_MISC or spilled SCALAR_VALUE register.

The effect of this (now) trivial change is huge, as can be seen below.
These are differences between BPF selftests, Cilium, and Meta-internal
BPF object files relative to previous patch in this series. You can see
improvements ranging from single-digit percentage improvement for
instructions and states, all the way to 50-60% reduction for some of
Meta-internal host agent programs, and even some Cilium programs.

For Meta-internal ones I left only the differences for largest BPF
object files by states/instructions, as there were too many differences
in the overall output. All the differences were improvements, reducting
number of states and thus instructions validated.

Note, Meta-internal BPF object file names are not printed below.
Many copies of balancer_ingress are actually many different
configurations of Katran, so they are different BPF programs, which
explains state reduction going from -16% all the way to 31%, depending
on BPF program logic complexity.

I also tooked a closer look at a few small-ish BPF programs to validate
the behavior. Let's take bpf_iter_netrlink.bpf.o (first row below).
While it's just 8 vs 5 states, verifier log is still pretty long to
include it here. But the reduction in states is due to the following
piece of C code:

        unsigned long ino;

	...

        sk = s->sk_socket;
        if (!sk) {
                ino = 0;
        } else {
                inode = SOCK_INODE(sk);
                bpf_probe_read_kernel(&ino, sizeof(ino), &inode->i_ino);
        }
        BPF_SEQ_PRINTF(seq, "%-8u %-8lu\n", s->sk_drops.counter, ino);
	return 0;

You can see that in some situations `ino` is zero-initialized, while in
others it's unknown value filled out by bpf_probe_read_kernel(). Before
this change code after if/else branches have to be validated twice. Once
with (precise) ino == 0, due to eager STACK_ZERO logic, and then again
for when ino is just STACK_MISC. But BPF_SEQ_PRINTF() doesn't care about
precise value of ino, so with the change in this patch verifier is able
to prune states from after one of the branches, reducing number of total
states (and instructions) required for successful validation.

Similar principle applies to bigger real-world applications, just at
a much larger scale.

SELFTESTS
=========
File                                     Program                  Insns (A)  Insns (B)  Insns    (DIFF)  States (A)  States (B)  States (DIFF)
---------------------------------------  -----------------------  ---------  ---------  ---------------  ----------  ----------  -------------
bpf_iter_netlink.bpf.linked3.o           dump_netlink                   148        104    -44 (-29.73%)           8           5   -3 (-37.50%)
bpf_iter_unix.bpf.linked3.o              dump_unix                     8474       8404     -70 (-0.83%)         151         147    -4 (-2.65%)
bpf_loop.bpf.linked3.o                   stack_check                    560        324   -236 (-42.14%)          42          24  -18 (-42.86%)
local_storage_bench.bpf.linked3.o        get_local                      120         77    -43 (-35.83%)           9           6   -3 (-33.33%)
loop6.bpf.linked3.o                      trace_virtqueue_add_sgs      10167       9868    -299 (-2.94%)         226         206   -20 (-8.85%)
pyperf600_bpf_loop.bpf.linked3.o         on_event                      4872       3423  -1449 (-29.74%)         322         229  -93 (-28.88%)
strobemeta.bpf.linked3.o                 on_event                    180697     176036   -4661 (-2.58%)        4780        4734   -46 (-0.96%)
test_cls_redirect.bpf.linked3.o          cls_redirect                 65594      65401    -193 (-0.29%)        4230        4212   -18 (-0.43%)
test_global_func_args.bpf.linked3.o      test_cls                       145        136      -9 (-6.21%)          10           9   -1 (-10.00%)
test_l4lb.bpf.linked3.o                  balancer_ingress              4760       2612  -2148 (-45.13%)         113         102   -11 (-9.73%)
test_l4lb_noinline.bpf.linked3.o         balancer_ingress              4845       4877     +32 (+0.66%)         219         221    +2 (+0.91%)
test_l4lb_noinline_dynptr.bpf.linked3.o  balancer_ingress              2072       2087     +15 (+0.72%)          97          98    +1 (+1.03%)
test_seg6_loop.bpf.linked3.o             __add_egr_x                  12440       9975  -2465 (-19.82%)         364         353   -11 (-3.02%)
test_tcp_hdr_options.bpf.linked3.o       estab                         2558       2572     +14 (+0.55%)         179         180    +1 (+0.56%)
test_xdp_dynptr.bpf.linked3.o            _xdp_tx_iptunnel               645        596     -49 (-7.60%)          26          24    -2 (-7.69%)
test_xdp_noinline.bpf.linked3.o          balancer_ingress_v6           3520       3516      -4 (-0.11%)         216         216    +0 (+0.00%)
xdp_synproxy_kern.bpf.linked3.o          syncookie_tc                 82661      81241   -1420 (-1.72%)        5073        5155   +82 (+1.62%)
xdp_synproxy_kern.bpf.linked3.o          syncookie_xdp                84964      82297   -2667 (-3.14%)        5130        5157   +27 (+0.53%)

META-INTERNAL
=============
Program                                 Insns (A)  Insns (B)  Insns      (DIFF)  States (A)  States (B)  States   (DIFF)
--------------------------------------  ---------  ---------  -----------------  ----------  ----------  ---------------
balancer_ingress                            27925      23608    -4317 (-15.46%)        1488        1482      -6 (-0.40%)
balancer_ingress                            31824      27546    -4278 (-13.44%)        1658        1652      -6 (-0.36%)
balancer_ingress                            32213      27935    -4278 (-13.28%)        1689        1683      -6 (-0.36%)
balancer_ingress                            32213      27935    -4278 (-13.28%)        1689        1683      -6 (-0.36%)
balancer_ingress                            31824      27546    -4278 (-13.44%)        1658        1652      -6 (-0.36%)
balancer_ingress                            38647      29562    -9085 (-23.51%)        2069        1835   -234 (-11.31%)
balancer_ingress                            38647      29562    -9085 (-23.51%)        2069        1835   -234 (-11.31%)
balancer_ingress                            40339      30792    -9547 (-23.67%)        2193        1934   -259 (-11.81%)
balancer_ingress                            37321      29055    -8266 (-22.15%)        1972        1795    -177 (-8.98%)
balancer_ingress                            38176      29753    -8423 (-22.06%)        2008        1831    -177 (-8.81%)
balancer_ingress                            29193      20910    -8283 (-28.37%)        1599        1422   -177 (-11.07%)
balancer_ingress                            30013      21452    -8561 (-28.52%)        1645        1447   -198 (-12.04%)
balancer_ingress                            28691      24290    -4401 (-15.34%)        1545        1531     -14 (-0.91%)
balancer_ingress                            34223      28965    -5258 (-15.36%)        1984        1875    -109 (-5.49%)
balancer_ingress                            35481      26158    -9323 (-26.28%)        2095        1806   -289 (-13.79%)
balancer_ingress                            35481      26158    -9323 (-26.28%)        2095        1806   -289 (-13.79%)
balancer_ingress                            35868      26455    -9413 (-26.24%)        2140        1827   -313 (-14.63%)
balancer_ingress                            35868      26455    -9413 (-26.24%)        2140        1827   -313 (-14.63%)
balancer_ingress                            35481      26158    -9323 (-26.28%)        2095        1806   -289 (-13.79%)
balancer_ingress                            35481      26158    -9323 (-26.28%)        2095        1806   -289 (-13.79%)
balancer_ingress                            34844      29485    -5359 (-15.38%)        2036        1918    -118 (-5.80%)
fbflow_egress                                3256       2652     -604 (-18.55%)         218         192    -26 (-11.93%)
fbflow_ingress                               1026        944       -82 (-7.99%)          70          63     -7 (-10.00%)
sslwall_tc_egress                            8424       7360    -1064 (-12.63%)         498         458     -40 (-8.03%)
syar_accept_protect                         15040       9539    -5501 (-36.58%)         364         220   -144 (-39.56%)
syar_connect_tcp_v6                         15036       9535    -5501 (-36.59%)         360         216   -144 (-40.00%)
syar_connect_udp_v4                         15039       9538    -5501 (-36.58%)         361         217   -144 (-39.89%)
syar_connect_connect4_protect4              24805      15833    -8972 (-36.17%)         756         480   -276 (-36.51%)
syar_lsm_file_open                         167772     151813    -15959 (-9.51%)        1836        1667    -169 (-9.20%)
syar_namespace_create_new                   14805       9304    -5501 (-37.16%)         353         209   -144 (-40.79%)
syar_python3_detect                         17531      12030    -5501 (-31.38%)         391         247   -144 (-36.83%)
syar_ssh_post_fork                          16412      10911    -5501 (-33.52%)         405         261   -144 (-35.56%)
syar_enter_execve                           14728       9227    -5501 (-37.35%)         345         201   -144 (-41.74%)
syar_enter_execveat                         14728       9227    -5501 (-37.35%)         345         201   -144 (-41.74%)
syar_exit_execve                            16622      11121    -5501 (-33.09%)         376         232   -144 (-38.30%)
syar_exit_execveat                          16622      11121    -5501 (-33.09%)         376         232   -144 (-38.30%)
syar_syscalls_kill                          15288       9787    -5501 (-35.98%)         398         254   -144 (-36.18%)
syar_task_enter_pivot_root                  14898       9397    -5501 (-36.92%)         357         213   -144 (-40.34%)
syar_syscalls_setreuid                      16678      11177    -5501 (-32.98%)         429         285   -144 (-33.57%)
syar_syscalls_setuid                        16678      11177    -5501 (-32.98%)         429         285   -144 (-33.57%)
syar_syscalls_process_vm_readv              14959       9458    -5501 (-36.77%)         364         220   -144 (-39.56%)
syar_syscalls_process_vm_writev             15757      10256    -5501 (-34.91%)         390         246   -144 (-36.92%)
do_uprobe                                   15519      10018    -5501 (-35.45%)         373         229   -144 (-38.61%)
edgewall                                   179715      55783  -123932 (-68.96%)       12607        3999  -8608 (-68.28%)
bictcp_state                                 7570       4131    -3439 (-45.43%)         496         269   -227 (-45.77%)
cubictcp_state                               7570       4131    -3439 (-45.43%)         496         269   -227 (-45.77%)
tcp_rate_skb_delivered                        447        272     -175 (-39.15%)          29          18    -11 (-37.93%)
kprobe__bbr_set_state                        4566       2615    -1951 (-42.73%)         209         124    -85 (-40.67%)
kprobe__bictcp_state                         4566       2615    -1951 (-42.73%)         209         124    -85 (-40.67%)
inet_sock_set_state                          1501       1337     -164 (-10.93%)          93          85      -8 (-8.60%)
tcp_retransmit_skb                           1145        981     -164 (-14.32%)          67          59     -8 (-11.94%)
tcp_retransmit_synack                        1183        951     -232 (-19.61%)          67          55    -12 (-17.91%)
bpf_tcptuner                                 1459       1187     -272 (-18.64%)          99          80    -19 (-19.19%)
tw_egress                                     801        776       -25 (-3.12%)          69          66      -3 (-4.35%)
tw_ingress                                    795        770       -25 (-3.14%)          69          66      -3 (-4.35%)
ttls_tc_ingress                             19025      19383      +358 (+1.88%)         470         465      -5 (-1.06%)
ttls_nat_egress                               490        299     -191 (-38.98%)          33          20    -13 (-39.39%)
ttls_nat_ingress                              448        285     -163 (-36.38%)          32          21    -11 (-34.38%)
tw_twfw_egress                             511127     212071  -299056 (-58.51%)       16733        8504  -8229 (-49.18%)
tw_twfw_ingress                            500095     212069  -288026 (-57.59%)       16223        8504  -7719 (-47.58%)
tw_twfw_tc_eg                              511113     212064  -299049 (-58.51%)       16732        8504  -8228 (-49.18%)
tw_twfw_tc_in                              500095     212069  -288026 (-57.59%)       16223        8504  -7719 (-47.58%)
tw_twfw_egress                              12632      12435      -197 (-1.56%)         276         260     -16 (-5.80%)
tw_twfw_ingress                             12631      12454      -177 (-1.40%)         278         261     -17 (-6.12%)
tw_twfw_tc_eg                               12595      12435      -160 (-1.27%)         274         259     -15 (-5.47%)
tw_twfw_tc_in                               12631      12454      -177 (-1.40%)         278         261     -17 (-6.12%)
tw_xdp_dump                                   266        209      -57 (-21.43%)           9           8     -1 (-11.11%)

CILIUM
=========
File           Program                           Insns (A)  Insns (B)  Insns     (DIFF)  States (A)  States (B)  States  (DIFF)
-------------  --------------------------------  ---------  ---------  ----------------  ----------  ----------  --------------
bpf_host.o     cil_to_netdev                          6047       4578   -1469 (-24.29%)         362         249  -113 (-31.22%)
bpf_host.o     handle_lxc_traffic                     2227       1585    -642 (-28.83%)         156         103   -53 (-33.97%)
bpf_host.o     tail_handle_ipv4_from_netdev           2244       1458    -786 (-35.03%)         163         106   -57 (-34.97%)
bpf_host.o     tail_handle_nat_fwd_ipv4              21022      10479  -10543 (-50.15%)        1289         670  -619 (-48.02%)
bpf_host.o     tail_handle_nat_fwd_ipv6              15433      11375   -4058 (-26.29%)         905         643  -262 (-28.95%)
bpf_host.o     tail_ipv4_host_policy_ingress          2219       1367    -852 (-38.40%)         161          96   -65 (-40.37%)
bpf_host.o     tail_nodeport_nat_egress_ipv4         22460      19862   -2598 (-11.57%)        1469        1293  -176 (-11.98%)
bpf_host.o     tail_nodeport_nat_ingress_ipv4         5526       3534   -1992 (-36.05%)         366         243  -123 (-33.61%)
bpf_host.o     tail_nodeport_nat_ingress_ipv6         5132       4256    -876 (-17.07%)         241         219    -22 (-9.13%)
bpf_host.o     tail_nodeport_nat_ipv6_egress          3702       3542     -160 (-4.32%)         215         205    -10 (-4.65%)
bpf_lxc.o      tail_handle_nat_fwd_ipv4              21022      10479  -10543 (-50.15%)        1289         670  -619 (-48.02%)
bpf_lxc.o      tail_handle_nat_fwd_ipv6              15433      11375   -4058 (-26.29%)         905         643  -262 (-28.95%)
bpf_lxc.o      tail_ipv4_ct_egress                    5073       3374   -1699 (-33.49%)         262         172   -90 (-34.35%)
bpf_lxc.o      tail_ipv4_ct_ingress                   5093       3385   -1708 (-33.54%)         262         172   -90 (-34.35%)
bpf_lxc.o      tail_ipv4_ct_ingress_policy_only       5093       3385   -1708 (-33.54%)         262         172   -90 (-34.35%)
bpf_lxc.o      tail_ipv6_ct_egress                    4593       3878    -715 (-15.57%)         194         151   -43 (-22.16%)
bpf_lxc.o      tail_ipv6_ct_ingress                   4606       3891    -715 (-15.52%)         194         151   -43 (-22.16%)
bpf_lxc.o      tail_ipv6_ct_ingress_policy_only       4606       3891    -715 (-15.52%)         194         151   -43 (-22.16%)
bpf_lxc.o      tail_nodeport_nat_ingress_ipv4         5526       3534   -1992 (-36.05%)         366         243  -123 (-33.61%)
bpf_lxc.o      tail_nodeport_nat_ingress_ipv6         5132       4256    -876 (-17.07%)         241         219    -22 (-9.13%)
bpf_overlay.o  tail_handle_nat_fwd_ipv4              20524      10114  -10410 (-50.72%)        1271         638  -633 (-49.80%)
bpf_overlay.o  tail_nodeport_nat_egress_ipv4         22718      19490   -3228 (-14.21%)        1475        1275  -200 (-13.56%)
bpf_overlay.o  tail_nodeport_nat_ingress_ipv4         5526       3534   -1992 (-36.05%)         366         243  -123 (-33.61%)
bpf_overlay.o  tail_nodeport_nat_ingress_ipv6         5132       4256    -876 (-17.07%)         241         219    -22 (-9.13%)
bpf_overlay.o  tail_nodeport_nat_ipv6_egress          3638       3548      -90 (-2.47%)         209         203     -6 (-2.87%)
bpf_overlay.o  tail_rev_nodeport_lb4                  4368       3820    -548 (-12.55%)         248         215   -33 (-13.31%)
bpf_overlay.o  tail_rev_nodeport_lb6                  2867       2428    -439 (-15.31%)         167         140   -27 (-16.17%)
bpf_sock.o     cil_sock6_connect                      1718       1703      -15 (-0.87%)         100          99     -1 (-1.00%)
bpf_xdp.o      tail_handle_nat_fwd_ipv4              12917      12443     -474 (-3.67%)         875         849    -26 (-2.97%)
bpf_xdp.o      tail_handle_nat_fwd_ipv6              13515      13264     -251 (-1.86%)         715         702    -13 (-1.82%)
bpf_xdp.o      tail_lb_ipv4                          39492      36367    -3125 (-7.91%)        2430        2251   -179 (-7.37%)
bpf_xdp.o      tail_lb_ipv6                          80441      78058    -2383 (-2.96%)        3647        3523   -124 (-3.40%)
bpf_xdp.o      tail_nodeport_ipv6_dsr                 1038        901    -137 (-13.20%)          61          55     -6 (-9.84%)
bpf_xdp.o      tail_nodeport_nat_egress_ipv4         13027      12096     -931 (-7.15%)         868         809    -59 (-6.80%)
bpf_xdp.o      tail_nodeport_nat_ingress_ipv4         7617       5900   -1717 (-22.54%)         522         413  -109 (-20.88%)
bpf_xdp.o      tail_nodeport_nat_ingress_ipv6         7575       7395     -180 (-2.38%)         383         374     -9 (-2.35%)
bpf_xdp.o      tail_rev_nodeport_lb4                  6808       6739      -69 (-1.01%)         403         396     -7 (-1.74%)
bpf_xdp.o      tail_rev_nodeport_lb6                 16173      15847     -326 (-2.02%)        1010         990    -20 (-1.98%)

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-9-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index eaeb996ff56a..705582bdda68 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4666,8 +4666,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		return err;
 
 	mark_stack_slot_scratched(env, spi);
-	if (reg && !(off % BPF_REG_SIZE) && register_is_bounded(reg) &&
-	    !register_is_null(reg) && env->bpf_capable) {
+	if (reg && !(off % BPF_REG_SIZE) && register_is_bounded(reg) && env->bpf_capable) {
 		save_register_state(env, state, spi, reg, size);
 		/* Break the relation on a narrowing spill. */
 		if (fls64(reg->umax_value) > BITS_PER_BYTE * size)
@@ -4716,7 +4715,12 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		/* when we zero initialize stack slots mark them as such */
 		if ((reg && register_is_null(reg)) ||
 		    (!reg && is_bpf_st_mem(insn) && insn->imm == 0)) {
-			/* backtracking doesn't work for STACK_ZERO yet. */
+			/* STACK_ZERO case happened because register spill
+			 * wasn't properly aligned at the stack slot boundary,
+			 * so it's not a register spill anymore; force
+			 * originating register to be precise to make
+			 * STACK_ZERO correct for subsequent states
+			 */
 			err = mark_chain_precision(env, value_regno);
 			if (err)
 				return err;
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 08/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (6 preceding siblings ...)
  2026-05-11 16:24 ` [PATCH 6.6.y 07/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Paul Chaignon
@ 2026-05-11 16:24 ` Paul Chaignon
  2026-05-11 16:25 ` [PATCH 6.6.y 09/10] bpf: handle fake register spill to stack with BPF_ST_MEM instruction Paul Chaignon
                   ` (3 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:24 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 064e0bea19b356c5d5f48a4549d80a3c03ce898b ]

Enhance partial_stack_load_preserves_zeros subtest with detailed
precision propagation log checks. We know expect fp-16 to be spilled,
initially imprecise, zero const register, which is later marked as
precise even when partial stack slot load is performed, even if it's not
a register fill (!).

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-10-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_spill_fill.c    | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index 41fd61299eab..df4920da3472 100644
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -495,6 +495,22 @@ char single_byte_buf[1] SEC(".data.single_byte_buf");
 SEC("raw_tp")
 __log_level(2)
 __success
+/* make sure fp-8 is all STACK_ZERO */
+__msg("2: (7a) *(u64 *)(r10 -8) = 0          ; R10=fp0 fp-8_w=00000000")
+/* but fp-16 is spilled IMPRECISE zero const reg */
+__msg("4: (7b) *(u64 *)(r10 -16) = r0        ; R0_w=0 R10=fp0 fp-16_w=0")
+/* and now check that precision propagation works even for such tricky case */
+__msg("10: (71) r2 = *(u8 *)(r10 -9)         ; R2_w=P0 R10=fp0 fp-16_w=0")
+__msg("11: (0f) r1 += r2")
+__msg("mark_precise: frame0: last_idx 11 first_idx 0 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r2 stack= before 10: (71) r2 = *(u8 *)(r10 -9)")
+__msg("mark_precise: frame0: regs= stack=-16 before 9: (bf) r1 = r6")
+__msg("mark_precise: frame0: regs= stack=-16 before 8: (73) *(u8 *)(r1 +0) = r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 7: (0f) r1 += r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 6: (71) r2 = *(u8 *)(r10 -1)")
+__msg("mark_precise: frame0: regs= stack=-16 before 5: (bf) r1 = r6")
+__msg("mark_precise: frame0: regs= stack=-16 before 4: (7b) *(u64 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 3: (b7) r0 = 0")
 __naked void partial_stack_load_preserves_zeros(void)
 {
 	asm volatile (
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 09/10] bpf: handle fake register spill to stack with BPF_ST_MEM instruction
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (7 preceding siblings ...)
  2026-05-11 16:24 ` [PATCH 6.6.y 08/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros Paul Chaignon
@ 2026-05-11 16:25 ` Paul Chaignon
  2026-05-11 16:25 ` [PATCH 6.6.y 10/10] selftests/bpf: validate fake register spill/fill precision backtracking logic Paul Chaignon
                   ` (2 subsequent siblings)
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:25 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 482d548d40b0af9af730e4869903d4433e44f014 ]

When verifier validates BPF_ST_MEM instruction that stores known
constant to stack (e.g., *(u64 *)(r10 - 8) = 123), it effectively spills
a fake register with a constant (but initially imprecise) value to
a stack slot. Because read-side logic treats it as a proper register
fill from stack slot, we need to mark such stack slot initialization as
INSN_F_STACK_ACCESS instruction to stop precision backtracking from
missing it.

Fixes: 41f6f64e6999 ("bpf: support non-r10 register spill/fill to/from stack in precision tracking")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20231209010958.66758-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/verifier.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 705582bdda68..f6040169ef74 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4678,7 +4678,6 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		__mark_reg_known(&fake_reg, insn->imm);
 		fake_reg.type = SCALAR_VALUE;
 		save_register_state(env, state, spi, &fake_reg, size);
-		insn_flags = 0; /* not a register spill */
 	} else if (reg && is_spillable_regtype(reg->type)) {
 		/* register containing pointer is being spilled into stack */
 		if (size != BPF_REG_SIZE) {
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* [PATCH 6.6.y 10/10] selftests/bpf: validate fake register spill/fill precision backtracking logic
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (8 preceding siblings ...)
  2026-05-11 16:25 ` [PATCH 6.6.y 09/10] bpf: handle fake register spill to stack with BPF_ST_MEM instruction Paul Chaignon
@ 2026-05-11 16:25 ` Paul Chaignon
  2026-05-12  0:17 ` [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Sasha Levin
  2026-05-12  6:51 ` Levi Zim
  11 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-11 16:25 UTC (permalink / raw)
  To: stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 7d8ed51bcb32716a40d71043fcd01c4118858c51 ]

Add two tests validating that verifier's precision backtracking logic
handles BPF_ST_MEM instructions that produce fake register spill into
register slot. This is happening when non-zero constant is written
directly to a slot, e.g., *(u64 *)(r10 -8) = 123.

Add both full 64-bit register spill, as well as 32-bit "sub-spill".

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20231209010958.66758-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[ Note: Adapted the expected log format for the selftests because it
  changed later on in commits 67d43dfbb42d, 0c95c9fdb696, and
  1db747d75b1d. ]
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_spill_fill.c | 154 ++++++++++++++++++
 1 file changed, 154 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index df4920da3472..1f71f596d33f 100644
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -577,4 +577,158 @@ __naked void partial_stack_load_preserves_zeros(void)
 	: __clobber_common);
 }
 
+char two_byte_buf[2] SEC(".data.two_byte_buf");
+
+SEC("raw_tp")
+__log_level(2) __flag(BPF_F_TEST_STATE_FREQ)
+__success
+/* make sure fp-8 is IMPRECISE fake register spill */
+__msg("3: (7a) *(u64 *)(r10 -8) = 1          ; R10=fp0 fp-8_w=1")
+/* and fp-16 is spilled IMPRECISE const reg */
+__msg("5: (7b) *(u64 *)(r10 -16) = r0        ; R0_w=1 R10=fp0 fp-16_w=1")
+/* validate load from fp-8, which was initialized using BPF_ST_MEM */
+__msg("8: (79) r2 = *(u64 *)(r10 -8)         ; R2_w=1 R10=fp0 fp-8=1")
+__msg("9: (0f) r1 += r2")
+__msg("mark_precise: frame0: last_idx 9 first_idx 7 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r2 stack= before 8: (79) r2 = *(u64 *)(r10 -8)")
+__msg("mark_precise: frame0: regs= stack=-8 before 7: (bf) r1 = r6")
+/* note, fp-8 is precise, fp-16 is not yet precise, we'll get there */
+__msg("mark_precise: frame0: parent state regs= stack=-8:  R0_w=1 R1=ctx(off=0,imm=0) R6_r=map_value(off=0,ks=4,vs=2,imm=0) R10=fp0 fp-8_rw=P1 fp-16_w=1")
+__msg("mark_precise: frame0: last_idx 6 first_idx 3 subseq_idx 7")
+__msg("mark_precise: frame0: regs= stack=-8 before 6: (05) goto pc+0")
+__msg("mark_precise: frame0: regs= stack=-8 before 5: (7b) *(u64 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r0 = 1")
+__msg("mark_precise: frame0: regs= stack=-8 before 3: (7a) *(u64 *)(r10 -8) = 1")
+__msg("10: R1_w=map_value(off=1,ks=4,vs=2,imm=0) R2_w=1")
+/* validate load from fp-16, which was initialized using BPF_STX_MEM */
+__msg("12: (79) r2 = *(u64 *)(r10 -16)       ; R2_w=1 R10=fp0 fp-16=1")
+__msg("13: (0f) r1 += r2")
+__msg("mark_precise: frame0: last_idx 13 first_idx 7 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r2 stack= before 12: (79) r2 = *(u64 *)(r10 -16)")
+__msg("mark_precise: frame0: regs= stack=-16 before 11: (bf) r1 = r6")
+__msg("mark_precise: frame0: regs= stack=-16 before 10: (73) *(u8 *)(r1 +0) = r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 9: (0f) r1 += r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 8: (79) r2 = *(u64 *)(r10 -8)")
+__msg("mark_precise: frame0: regs= stack=-16 before 7: (bf) r1 = r6")
+/* now both fp-8 and fp-16 are precise, very good */
+__msg("mark_precise: frame0: parent state regs= stack=-16:  R0_w=1 R1=ctx(off=0,imm=0) R6_r=map_value(off=0,ks=4,vs=2,imm=0) R10=fp0 fp-8_rw=P1 fp-16_rw=P1")
+__msg("mark_precise: frame0: last_idx 6 first_idx 3 subseq_idx 7")
+__msg("mark_precise: frame0: regs= stack=-16 before 6: (05) goto pc+0")
+__msg("mark_precise: frame0: regs= stack=-16 before 5: (7b) *(u64 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 4: (b7) r0 = 1")
+__msg("14: R1_w=map_value(off=1,ks=4,vs=2,imm=0) R2_w=1")
+__naked void stack_load_preserves_const_precision(void)
+{
+	asm volatile (
+		/* establish checkpoint with state that has no stack slots;
+		 * if we bubble up to this state without finding desired stack
+		 * slot, then it's a bug and should be caught
+		 */
+		"goto +0;"
+
+		/* fp-8 is const 1 *fake* register */
+		".8byte %[fp8_st_one];" /* LLVM-18+: *(u64 *)(r10 -8) = 1; */
+
+		/* fp-16 is const 1 register */
+		"r0 = 1;"
+		"*(u64 *)(r10 -16) = r0;"
+
+		/* force checkpoint to check precision marks preserved in parent states */
+		"goto +0;"
+
+		/* load single U64 from aligned FAKE_REG=1 slot */
+		"r1 = %[two_byte_buf];"
+		"r2 = *(u64 *)(r10 -8);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U64 from aligned REG=1 slot */
+		"r1 = %[two_byte_buf];"
+		"r2 = *(u64 *)(r10 -16);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		"r0 = 0;"
+		"exit;"
+	:
+	: __imm_ptr(two_byte_buf),
+	  __imm_insn(fp8_st_one, BPF_ST_MEM(BPF_DW, BPF_REG_FP, -8, 1))
+	: __clobber_common);
+}
+
+SEC("raw_tp")
+__log_level(2) __flag(BPF_F_TEST_STATE_FREQ)
+__success
+/* make sure fp-8 is 32-bit FAKE subregister spill */
+__msg("3: (62) *(u32 *)(r10 -8) = 1          ; R10=fp0 fp-8=1")
+/* but fp-16 is spilled IMPRECISE zero const reg */
+__msg("5: (63) *(u32 *)(r10 -16) = r0        ; R0_w=1 R10=fp0 fp-16=1")
+/* validate load from fp-8, which was initialized using BPF_ST_MEM */
+__msg("8: (61) r2 = *(u32 *)(r10 -8)         ; R2_w=1 R10=fp0 fp-8=1")
+__msg("9: (0f) r1 += r2")
+__msg("mark_precise: frame0: last_idx 9 first_idx 7 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r2 stack= before 8: (61) r2 = *(u32 *)(r10 -8)")
+__msg("mark_precise: frame0: regs= stack=-8 before 7: (bf) r1 = r6")
+__msg("mark_precise: frame0: parent state regs= stack=-8:  R0_w=1 R1=ctx(off=0,imm=0) R6_r=map_value(off=0,ks=4,vs=2,imm=0) R10=fp0 fp-8_r=P1 fp-16=1")
+__msg("mark_precise: frame0: last_idx 6 first_idx 3 subseq_idx 7")
+__msg("mark_precise: frame0: regs= stack=-8 before 6: (05) goto pc+0")
+__msg("mark_precise: frame0: regs= stack=-8 before 5: (63) *(u32 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r0 = 1")
+__msg("mark_precise: frame0: regs= stack=-8 before 3: (62) *(u32 *)(r10 -8) = 1")
+__msg("10: R1_w=map_value(off=1,ks=4,vs=2,imm=0) R2_w=1")
+/* validate load from fp-16, which was initialized using BPF_STX_MEM */
+__msg("12: (61) r2 = *(u32 *)(r10 -16)       ; R2_w=1 R10=fp0 fp-16=1")
+__msg("13: (0f) r1 += r2")
+__msg("mark_precise: frame0: last_idx 13 first_idx 7 subseq_idx -1")
+__msg("mark_precise: frame0: regs=r2 stack= before 12: (61) r2 = *(u32 *)(r10 -16)")
+__msg("mark_precise: frame0: regs= stack=-16 before 11: (bf) r1 = r6")
+__msg("mark_precise: frame0: regs= stack=-16 before 10: (73) *(u8 *)(r1 +0) = r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 9: (0f) r1 += r2")
+__msg("mark_precise: frame0: regs= stack=-16 before 8: (61) r2 = *(u32 *)(r10 -8)")
+__msg("mark_precise: frame0: regs= stack=-16 before 7: (bf) r1 = r6")
+__msg("mark_precise: frame0: parent state regs= stack=-16:  R0_w=1 R1=ctx(off=0,imm=0) R6_r=map_value(off=0,ks=4,vs=2,imm=0) R10=fp0 fp-8_r=P1 fp-16_r=P1")
+__msg("mark_precise: frame0: last_idx 6 first_idx 3 subseq_idx 7")
+__msg("mark_precise: frame0: regs= stack=-16 before 6: (05) goto pc+0")
+__msg("mark_precise: frame0: regs= stack=-16 before 5: (63) *(u32 *)(r10 -16) = r0")
+__msg("mark_precise: frame0: regs=r0 stack= before 4: (b7) r0 = 1")
+__msg("14: R1_w=map_value(off=1,ks=4,vs=2,imm=0) R2_w=1")
+__naked void stack_load_preserves_const_precision_subreg(void)
+{
+	asm volatile (
+		/* establish checkpoint with state that has no stack slots;
+		 * if we bubble up to this state without finding desired stack
+		 * slot, then it's a bug and should be caught
+		 */
+		"goto +0;"
+
+		/* fp-8 is const 1 *fake* SUB-register */
+		".8byte %[fp8_st_one];" /* LLVM-18+: *(u32 *)(r10 -8) = 1; */
+
+		/* fp-16 is const 1 SUB-register */
+		"r0 = 1;"
+		"*(u32 *)(r10 -16) = r0;"
+
+		/* force checkpoint to check precision marks preserved in parent states */
+		"goto +0;"
+
+		/* load single U32 from aligned FAKE_REG=1 slot */
+		"r1 = %[two_byte_buf];"
+		"r2 = *(u32 *)(r10 -8);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		/* load single U32 from aligned REG=1 slot */
+		"r1 = %[two_byte_buf];"
+		"r2 = *(u32 *)(r10 -16);"
+		"r1 += r2;"
+		"*(u8 *)(r1 + 0) = r2;" /* this should be fine */
+
+		"r0 = 0;"
+		"exit;"
+	:
+	: __imm_ptr(two_byte_buf),
+	  __imm_insn(fp8_st_one, BPF_ST_MEM(BPF_W, BPF_REG_FP, -8, 1)) /* 32-bit spill */
+	: __clobber_common);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
* Re: [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (9 preceding siblings ...)
  2026-05-11 16:25 ` [PATCH 6.6.y 10/10] selftests/bpf: validate fake register spill/fill precision backtracking logic Paul Chaignon
@ 2026-05-12  0:17 ` Sasha Levin
  2026-05-12 12:01   ` Paul Chaignon
  2026-05-12  6:51 ` Levi Zim
  11 siblings, 1 reply; 14+ messages in thread
From: Sasha Levin @ 2026-05-12  0:17 UTC (permalink / raw)
  To: stable
  Cc: Sasha Levin, Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim, Paul Chaignon

On Mon, May 11, 2026 at 06:21:22PM +0200, Paul Chaignon wrote:
> This patchset backports commit 41f6f64e6999 ("bpf: support non-r10
> register spill/fill to/from stack in precision tracking") again, but
> this time with the subsequent commits that improved the efficiency of
> the verifier. In addition, the last two commits fix and test a
> regression that was later found in commit 41f6f64e6999.

Queued for 6.6, thanks.

I also separately picked up 69772f509e08 ("bpf: Don't mark STACK_INVALID
as STACK_MISC in mark_stack_slot_misc") as a follow-up to patch 3/10
(eaf18febd6eb).

-- 
Thanks,
Sasha

^ permalink raw reply	[flat|nested] 14+ messages in thread
* Re: [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration
  2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
                   ` (10 preceding siblings ...)
  2026-05-12  0:17 ` [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Sasha Levin
@ 2026-05-12  6:51 ` Levi Zim
  11 siblings, 0 replies; 14+ messages in thread
From: Levi Zim @ 2026-05-12  6:51 UTC (permalink / raw)
  To: Paul Chaignon, stable
  Cc: Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu

On 2026-05-12 00:21, Paul Chaignon wrote:
> The first patch in this patchset was already backported before, as
> commit ecc2aeeaa08a, to address CVE-2023-52920 [1]. That backport was
> however later reverted in commit 199f04528737 because it reduced the
> efficiency of the BPF verifier, to the point that it rejected some
> previously-accepted programs.
>
> This patchset backports commit 41f6f64e6999 ("bpf: support non-r10
> register spill/fill to/from stack in precision tracking") again, but
> this time with the subsequent commits that improved the efficiency of
> the verifier. In addition, the last two commits fix and test a
> regression that was later found in commit 41f6f64e6999.

Thanks a lot!

I can confirm that the reproducer that originally led to the revert 
could load successfully
with this patchset.

Tested-By: Levi Zim <rsworktech@outlook.com>

Best regards,
Levi

>
> It took us a while with Shung-Hsi to come back to this because we felt
> we didn't have enough test coverage to backport this. That changed with
> the stable BPF CI Shung-Hsi built for v6.6, which successfully
> validated this patchset [2]. In addition, I tested the impact of this
> patchset on the verifier's efficiency with Cilium's BPF programs [3]:
> it significantly improves, reducing the number of instructions the
> verifier has to analyze by up to 87% in some cases!
>
> 1: https://lore.kernel.org/linux-cve-announce/2024110518-CVE-2023-52920-17f6@gregkh/
> 2: https://github.com/pchaigno/stable-bpf-ci/actions/runs/25671397661/job/75357317078
> 3: https://pchaigno.github.io/test-verifier-complexity.html
>
> Andrii Nakryiko (10):
>    bpf: support non-r10 register spill/fill to/from stack in precision
>      tracking
>    selftests/bpf: add stack access precision test
>    bpf: preserve STACK_ZERO slots on partial reg spills
>    selftests/bpf: validate STACK_ZERO is preserved on subreg spill
>    bpf: preserve constant zero when doing partial register restore
>    selftests/bpf: validate zero preservation for sub-slot loads
>    bpf: track aligned STACK_ZERO cases as imprecise spilled registers
>    selftests/bpf: validate precision logic in
>      partial_stack_load_preserves_zeros
>    bpf: handle fake register spill to stack with BPF_ST_MEM instruction
>    selftests/bpf: validate fake register spill/fill precision
>      backtracking logic
>
>   include/linux/bpf_verifier.h                  |  31 +-
>   kernel/bpf/verifier.c                         | 233 +++++++++------
>   .../selftests/bpf/progs/verifier_spill_fill.c | 281 ++++++++++++++++++
>   .../bpf/progs/verifier_subprog_precision.c    |  87 +++++-
>   .../testing/selftests/bpf/verifier/precise.c  |  38 ++-
>   5 files changed, 557 insertions(+), 113 deletions(-)
>

^ permalink raw reply	[flat|nested] 14+ messages in thread
* Re: [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration
  2026-05-12  0:17 ` [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Sasha Levin
@ 2026-05-12 12:01   ` Paul Chaignon
  0 siblings, 0 replies; 14+ messages in thread
From: Paul Chaignon @ 2026-05-12 12:01 UTC (permalink / raw)
  To: Sasha Levin
  Cc: stable, Greg Kroah-Hartman, Shung-Hsi Yu, Daniel Borkmann,
	Alexei Starovoitov, Eduard Zingerman, Andrii Nakryiko, Tao Lyu,
	Levi Zim

On Mon, May 11, 2026 at 08:17:53PM -0400, Sasha Levin wrote:
> On Mon, May 11, 2026 at 06:21:22PM +0200, Paul Chaignon wrote:
> > This patchset backports commit 41f6f64e6999 ("bpf: support non-r10
> > register spill/fill to/from stack in precision tracking") again, but
> > this time with the subsequent commits that improved the efficiency of
> > the verifier. In addition, the last two commits fix and test a
> > regression that was later found in commit 41f6f64e6999.
> 
> Queued for 6.6, thanks.
> 
> I also separately picked up 69772f509e08 ("bpf: Don't mark STACK_INVALID
> as STACK_MISC in mark_stack_slot_misc") as a follow-up to patch 3/10
> (eaf18febd6eb).

Thanks! I had missed that one. I can confirm v6.6 BPF selftests are
still green with that additional patch:
https://github.com/pchaigno/stable-bpf-ci/actions/runs/25726612531/job/75540955361.

> 
> -- 
> Thanks,
> Sasha

^ permalink raw reply	[flat|nested] 14+ messages in thread
end of thread, other threads:[~2026-05-12 12:01 UTC | newest]

Thread overview: 14+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-05-11 16:21 [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Paul Chaignon
2026-05-11 16:22 ` [PATCH 6.6.y 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Paul Chaignon
2026-05-11 16:23 ` [PATCH 6.6.y 02/10] selftests/bpf: add stack access precision test Paul Chaignon
2026-05-11 16:23 ` [PATCH 6.6.y 03/10] bpf: preserve STACK_ZERO slots on partial reg spills Paul Chaignon
2026-05-11 16:24 ` [PATCH 6.6.y 04/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill Paul Chaignon
2026-05-11 16:24 ` [PATCH 6.6.y 05/10] bpf: preserve constant zero when doing partial register restore Paul Chaignon
2026-05-11 16:24 ` [PATCH 6.6.y 06/10] selftests/bpf: validate zero preservation for sub-slot loads Paul Chaignon
2026-05-11 16:24 ` [PATCH 6.6.y 07/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Paul Chaignon
2026-05-11 16:24 ` [PATCH 6.6.y 08/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros Paul Chaignon
2026-05-11 16:25 ` [PATCH 6.6.y 09/10] bpf: handle fake register spill to stack with BPF_ST_MEM instruction Paul Chaignon
2026-05-11 16:25 ` [PATCH 6.6.y 10/10] selftests/bpf: validate fake register spill/fill precision backtracking logic Paul Chaignon
2026-05-12  0:17 ` [PATCH 6.6.y 00/10] bpf: fix precision backtracking instruction iteration Sasha Levin
2026-05-12 12:01   ` Paul Chaignon
2026-05-12  6:51 ` Levi Zim

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