Merge branch 'bpf-reduce-verifier-stack-frame-size'

Yonghong Song says:

====================
bpf: Reduce verifier stack frame size

Arnd Bergmann reported an issue ([1]) where clang compiler (less than
llvm18) may trigger an error where the stack frame size exceeds the limit.
I can reproduce the error like below:
  kernel/bpf/verifier.c:24491:5: error: stack frame size (2552) exceeds limit (1280) in 'bpf_check'
      [-Werror,-Wframe-larger-than]
  kernel/bpf/verifier.c:19921:12: error: stack frame size (1368) exceeds limit (1280) in 'do_check'
      [-Werror,-Wframe-larger-than]

This patch series fixed the above two errors by reducing stack size.
See each individual patches for details.

  [1] https://lore.kernel.org/bpf/20250620113846.3950478-1-arnd@kernel.org/

Changelogs:
  v2 -> v3:
    - v2: https://lore.kernel.org/bpf/20250702171134.2370432-1-yonghong.song@linux.dev/
    - Rename env->callchain to env->callchain_buf so it is clear that
    - env->callchain_buf is used for a temp buf.

  v1 -> v2:
    - v1: https://lore.kernel.org/bpf/20250702053332.1991516-1-yonghong.song@linux.dev/
    - Simplify assignment to struct bpf_insn pointer in do_misc_fixups().
    - Restore original implementation in opt_hard_wire_dead_code_branches()
      as only one insn on the stack.
    - Avoid unnecessary insns for 64bit modulo (mod 0/-1) operations.
====================

Link: https://patch.msgid.link/20250703141101.1482025-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -841,6 +841,7 @@ struct bpf_verifier_env {
 	char tmp_str_buf[TMP_STR_BUF_LEN];
 	struct bpf_insn insn_buf[INSN_BUF_SIZE];
 	struct bpf_insn epilogue_buf[INSN_BUF_SIZE];
+	struct bpf_scc_callchain callchain_buf;
 	/* array of pointers to bpf_scc_info indexed by SCC id */
 	struct bpf_scc_info **scc_info;
 	u32 scc_cnt;

kernel/bpf/verifier.c

@@ -1914,19 +1914,19 @@ static char *format_callchain(struct bpf_verifier_env *env, struct bpf_scc_callc
  */
 static int maybe_enter_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain_buf;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return 0;
-	visit = scc_visit_lookup(env, &callchain);
-	visit = visit ?: scc_visit_alloc(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
+	visit = visit ?: scc_visit_alloc(env, callchain);
 	if (!visit)
 		return -ENOMEM;
 	if (!visit->entry_state) {
 		visit->entry_state = st;
 		if (env->log.level & BPF_LOG_LEVEL2)
-			verbose(env, "SCC enter %s\n", format_callchain(env, &callchain));
+			verbose(env, "SCC enter %s\n", format_callchain(env, callchain));
 	}
 	return 0;
 }
@@ -1939,21 +1939,21 @@ static int propagate_backedges(struct bpf_verifier_env *env, struct bpf_scc_visi
  */
 static int maybe_exit_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain_buf;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return 0;
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit) {
 		verifier_bug(env, "scc exit: no visit info for call chain %s",
-			     format_callchain(env, &callchain));
+			     format_callchain(env, callchain));
 		return -EFAULT;
 	}
 	if (visit->entry_state != st)
 		return 0;
 	if (env->log.level & BPF_LOG_LEVEL2)
-		verbose(env, "SCC exit %s\n", format_callchain(env, &callchain));
+		verbose(env, "SCC exit %s\n", format_callchain(env, callchain));
 	visit->entry_state = NULL;
 	env->num_backedges -= visit->num_backedges;
 	visit->num_backedges = 0;
@@ -1968,22 +1968,22 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
 			    struct bpf_verifier_state *st,
 			    struct bpf_scc_backedge *backedge)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain_buf;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain)) {
+	if (!compute_scc_callchain(env, st, callchain)) {
 		verifier_bug(env, "add backedge: no SCC in verification path, insn_idx %d",
 			     st->insn_idx);
 		return -EFAULT;
 	}
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit) {
 		verifier_bug(env, "add backedge: no visit info for call chain %s",
-			     format_callchain(env, &callchain));
+			     format_callchain(env, callchain));
 		return -EFAULT;
 	}
 	if (env->log.level & BPF_LOG_LEVEL2)
-		verbose(env, "SCC backedge %s\n", format_callchain(env, &callchain));
+		verbose(env, "SCC backedge %s\n", format_callchain(env, callchain));
 	backedge->next = visit->backedges;
 	visit->backedges = backedge;
 	visit->num_backedges++;
@@ -1999,12 +1999,12 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
 static bool incomplete_read_marks(struct bpf_verifier_env *env,
 				  struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain_buf;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return false;
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit)
 		return false;
 	return !!visit->backedges;
@@ -21011,7 +21011,10 @@ static int opt_remove_nops(struct bpf_verifier_env *env)
 static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
 					 const union bpf_attr *attr)
 {
-	struct bpf_insn *patch, zext_patch[2], rnd_hi32_patch[4];
+	struct bpf_insn *patch;
+	/* use env->insn_buf as two independent buffers */
+	struct bpf_insn *zext_patch = env->insn_buf;
+	struct bpf_insn *rnd_hi32_patch = &env->insn_buf[2];
 	struct bpf_insn_aux_data *aux = env->insn_aux_data;
 	int i, patch_len, delta = 0, len = env->prog->len;
 	struct bpf_insn *insns = env->prog->insnsi;
@@ -21189,13 +21192,12 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 
 		if (env->insn_aux_data[i + delta].nospec) {
 			WARN_ON_ONCE(env->insn_aux_data[i + delta].alu_state);
-			struct bpf_insn patch[] = {
-				BPF_ST_NOSPEC(),
-				*insn,
-			};
+			struct bpf_insn *patch = insn_buf;
 
-			cnt = ARRAY_SIZE(patch);
-			new_prog = bpf_patch_insn_data(env, i + delta, patch, cnt);
+			*patch++ = BPF_ST_NOSPEC();
+			*patch++ = *insn;
+			cnt = patch - insn_buf;
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
 			if (!new_prog)
 				return -ENOMEM;
 
@@ -21263,13 +21265,12 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 			/* nospec_result is only used to mitigate Spectre v4 and
 			 * to limit verification-time for Spectre v1.
 			 */
-			struct bpf_insn patch[] = {
-				*insn,
-				BPF_ST_NOSPEC(),
-			};
+			struct bpf_insn *patch = insn_buf;
 
-			cnt = ARRAY_SIZE(patch);
-			new_prog = bpf_patch_insn_data(env, i + delta, patch, cnt);
+			*patch++ = *insn;
+			*patch++ = BPF_ST_NOSPEC();
+			cnt = patch - insn_buf;
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
 			if (!new_prog)
 				return -ENOMEM;
 
@@ -21939,13 +21940,12 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 	u16 stack_depth_extra = 0;
 
 	if (env->seen_exception && !env->exception_callback_subprog) {
-		struct bpf_insn patch[] = {
-			env->prog->insnsi[insn_cnt - 1],
-			BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
-			BPF_EXIT_INSN(),
-		};
+		struct bpf_insn *patch = insn_buf;
 
-		ret = add_hidden_subprog(env, patch, ARRAY_SIZE(patch));
+		*patch++ = env->prog->insnsi[insn_cnt - 1];
+		*patch++ = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
+		*patch++ = BPF_EXIT_INSN();
+		ret = add_hidden_subprog(env, insn_buf, patch - insn_buf);
 		if (ret < 0)
 			return ret;
 		prog = env->prog;
@@ -21981,20 +21981,18 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		    insn->off == 1 && insn->imm == -1) {
 			bool is64 = BPF_CLASS(insn->code) == BPF_ALU64;
 			bool isdiv = BPF_OP(insn->code) == BPF_DIV;
-			struct bpf_insn *patchlet;
-			struct bpf_insn chk_and_sdiv[] = {
-				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
-					     BPF_NEG | BPF_K, insn->dst_reg,
-					     0, 0, 0),
-			};
-			struct bpf_insn chk_and_smod[] = {
-				BPF_MOV32_IMM(insn->dst_reg, 0),
-			};
+			struct bpf_insn *patch = insn_buf;
 
-			patchlet = isdiv ? chk_and_sdiv : chk_and_smod;
-			cnt = isdiv ? ARRAY_SIZE(chk_and_sdiv) : ARRAY_SIZE(chk_and_smod);
+			if (isdiv)
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
+							BPF_NEG | BPF_K, insn->dst_reg,
+							0, 0, 0);
+			else
+				*patch++ = BPF_MOV32_IMM(insn->dst_reg, 0);
 
-			new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt);
+			cnt = patch - insn_buf;
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
 			if (!new_prog)
 				return -ENOMEM;
 
@@ -22013,83 +22011,79 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			bool isdiv = BPF_OP(insn->code) == BPF_DIV;
 			bool is_sdiv = isdiv && insn->off == 1;
 			bool is_smod = !isdiv && insn->off == 1;
-			struct bpf_insn *patchlet;
-			struct bpf_insn chk_and_div[] = {
-				/* [R,W]x div 0 -> 0 */
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JNE | BPF_K, insn->src_reg,
-					     0, 2, 0),
-				BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg),
-				BPF_JMP_IMM(BPF_JA, 0, 0, 1),
-				*insn,
-			};
-			struct bpf_insn chk_and_mod[] = {
-				/* [R,W]x mod 0 -> [R,W]x */
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JEQ | BPF_K, insn->src_reg,
-					     0, 1 + (is64 ? 0 : 1), 0),
-				*insn,
-				BPF_JMP_IMM(BPF_JA, 0, 0, 1),
-				BPF_MOV32_REG(insn->dst_reg, insn->dst_reg),
-			};
-			struct bpf_insn chk_and_sdiv[] = {
+			struct bpf_insn *patch = insn_buf;
+
+			if (is_sdiv) {
 				/* [R,W]x sdiv 0 -> 0
 				 * LLONG_MIN sdiv -1 -> LLONG_MIN
 				 * INT_MIN sdiv -1 -> INT_MIN
 				 */
-				BPF_MOV64_REG(BPF_REG_AX, insn->src_reg),
-				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
-					     BPF_ADD | BPF_K, BPF_REG_AX,
-					     0, 0, 1),
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JGT | BPF_K, BPF_REG_AX,
-					     0, 4, 1),
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JEQ | BPF_K, BPF_REG_AX,
-					     0, 1, 0),
-				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
-					     BPF_MOV | BPF_K, insn->dst_reg,
-					     0, 0, 0),
+				*patch++ = BPF_MOV64_REG(BPF_REG_AX, insn->src_reg);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
+							BPF_ADD | BPF_K, BPF_REG_AX,
+							0, 0, 1);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JGT | BPF_K, BPF_REG_AX,
+							0, 4, 1);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JEQ | BPF_K, BPF_REG_AX,
+							0, 1, 0);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
+							BPF_MOV | BPF_K, insn->dst_reg,
+							0, 0, 0);
 				/* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */
-				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
-					     BPF_NEG | BPF_K, insn->dst_reg,
-					     0, 0, 0),
-				BPF_JMP_IMM(BPF_JA, 0, 0, 1),
-				*insn,
-			};
-			struct bpf_insn chk_and_smod[] = {
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
+							BPF_NEG | BPF_K, insn->dst_reg,
+							0, 0, 0);
+				*patch++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+				*patch++ = *insn;
+				cnt = patch - insn_buf;
+			} else if (is_smod) {
 				/* [R,W]x mod 0 -> [R,W]x */
 				/* [R,W]x mod -1 -> 0 */
-				BPF_MOV64_REG(BPF_REG_AX, insn->src_reg),
-				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
-					     BPF_ADD | BPF_K, BPF_REG_AX,
-					     0, 0, 1),
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JGT | BPF_K, BPF_REG_AX,
-					     0, 3, 1),
-				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
-					     BPF_JEQ | BPF_K, BPF_REG_AX,
-					     0, 3 + (is64 ? 0 : 1), 1),
-				BPF_MOV32_IMM(insn->dst_reg, 0),
-				BPF_JMP_IMM(BPF_JA, 0, 0, 1),
-				*insn,
-				BPF_JMP_IMM(BPF_JA, 0, 0, 1),
-				BPF_MOV32_REG(insn->dst_reg, insn->dst_reg),
-			};
+				*patch++ = BPF_MOV64_REG(BPF_REG_AX, insn->src_reg);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |
+							BPF_ADD | BPF_K, BPF_REG_AX,
+							0, 0, 1);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JGT | BPF_K, BPF_REG_AX,
+							0, 3, 1);
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JEQ | BPF_K, BPF_REG_AX,
+							0, 3 + (is64 ? 0 : 1), 1);
+				*patch++ = BPF_MOV32_IMM(insn->dst_reg, 0);
+				*patch++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+				*patch++ = *insn;
 
-			if (is_sdiv) {
-				patchlet = chk_and_sdiv;
-				cnt = ARRAY_SIZE(chk_and_sdiv);
-			} else if (is_smod) {
-				patchlet = chk_and_smod;
-				cnt = ARRAY_SIZE(chk_and_smod) - (is64 ? 2 : 0);
+				if (!is64) {
+					*patch++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+					*patch++ = BPF_MOV32_REG(insn->dst_reg, insn->dst_reg);
+				}
+				cnt = patch - insn_buf;
+			} else if (isdiv) {
+				/* [R,W]x div 0 -> 0 */
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JNE | BPF_K, insn->src_reg,
+							0, 2, 0);
+				*patch++ = BPF_ALU32_REG(BPF_XOR, insn->dst_reg, insn->dst_reg);
+				*patch++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+				*patch++ = *insn;
+				cnt = patch - insn_buf;
 			} else {
-				patchlet = isdiv ? chk_and_div : chk_and_mod;
-				cnt = isdiv ? ARRAY_SIZE(chk_and_div) :
-					      ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0);
+				/* [R,W]x mod 0 -> [R,W]x */
+				*patch++ = BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |
+							BPF_JEQ | BPF_K, insn->src_reg,
+							0, 1 + (is64 ? 0 : 1), 0);
+				*patch++ = *insn;
+
+				if (!is64) {
+					*patch++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+					*patch++ = BPF_MOV32_REG(insn->dst_reg, insn->dst_reg);
+				}
+				cnt = patch - insn_buf;
 			}
 
-			new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt);
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
 			if (!new_prog)
 				return -ENOMEM;
 
@@ -22103,7 +22097,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		if (BPF_CLASS(insn->code) == BPF_LDX &&
 		    (BPF_MODE(insn->code) == BPF_PROBE_MEM ||
 		     BPF_MODE(insn->code) == BPF_PROBE_MEMSX)) {
-			struct bpf_insn *patch = &insn_buf[0];
+			struct bpf_insn *patch = insn_buf;
 			u64 uaddress_limit = bpf_arch_uaddress_limit();
 
 			if (!uaddress_limit)
@@ -22154,7 +22148,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		    insn->code == (BPF_ALU64 | BPF_SUB | BPF_X)) {
 			const u8 code_add = BPF_ALU64 | BPF_ADD | BPF_X;
 			const u8 code_sub = BPF_ALU64 | BPF_SUB | BPF_X;
-			struct bpf_insn *patch = &insn_buf[0];
+			struct bpf_insn *patch = insn_buf;
 			bool issrc, isneg, isimm;
 			u32 off_reg;