Commit 45e9cd38 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

bpf: Reduce stack frame size by using env->insn_buf for bpf insns 

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]

Use env->insn_buf for bpf insns instead of putting these insns on the
stack. This can resolve the above 'bpf_check' error. The 'do_check' error
will be resolved in the next patch.

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



Reported-by: default avatarArnd Bergmann <arnd@kernel.org>
Tested-by: default avatarArnd Bergmann <arnd@arndb.de>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250703141111.1484521-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 3b872514

kernel/bpf/verifier.c

+92 −98
Original line number Diff line number Diff line
@@ -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) |









			struct bpf_insn *patch = insn_buf;

















			if (isdiv)









				*patch++ = 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),









			};









							0, 0, 0);









			else









				*patch++ = BPF_MOV32_IMM(insn->dst_reg, 0);

















			patchlet = isdiv ? chk_and_sdiv : chk_and_smod;









			cnt = isdiv ? ARRAY_SIZE(chk_and_sdiv) : ARRAY_SIZE(chk_and_smod);









			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;


















@@ -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) |









				*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),









				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |









							0, 0, 1);









				*patch++ = 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) |









							0, 4, 1);









				*patch++ = 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) |









							0, 1, 0);









				*patch++ = BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |









							BPF_MOV | BPF_K, insn->dst_reg,









					     0, 0, 0),









							0, 0, 0);









				/* BPF_NEG(LLONG_MIN) == -LLONG_MIN == LLONG_MIN */









				BPF_RAW_INSN((is64 ? BPF_ALU64 : BPF_ALU) |









				*patch++ = 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[] = {









							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) |









				*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),









				BPF_RAW_INSN((is64 ? BPF_JMP : BPF_JMP32) |









							0, 0, 1);









				*patch++ = 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) |









							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),









				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),









			};









							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;