Commit 1153583e authored by Yonghong Song's avatar Yonghong Song Committed by Xiaomeng Zhang
Browse files

bpf: Fix a sdiv overflow issue 

mainline inclusion
from mainline-v6.12-rc1
commit 7dd34d7b7dcf9309fc6224caf4dd5b35bedddcb7
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAYRCO
CVE: CVE-2024-49888

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7dd34d7b7dcf

--------------------------------

Zac Ecob reported a problem where a bpf program may cause kernel crash due
to the following error:
  Oops: divide error: 0000 [#1] PREEMPT SMP KASAN PTI

The failure is due to the below signed divide:
  LLONG_MIN/-1 where LLONG_MIN equals to -9,223,372,036,854,775,808.
LLONG_MIN/-1 is supposed to give a positive number 9,223,372,036,854,775,808,
but it is impossible since for 64-bit system, the maximum positive
number is 9,223,372,036,854,775,807. On x86_64, LLONG_MIN/-1 will
cause a kernel exception. On arm64, the result for LLONG_MIN/-1 is
LLONG_MIN.

Further investigation found all the following sdiv/smod cases may trigger
an exception when bpf program is running on x86_64 platform:
  - LLONG_MIN/-1 for 64bit operation
  - INT_MIN/-1 for 32bit operation
  - LLONG_MIN%-1 for 64bit operation
  - INT_MIN%-1 for 32bit operation
where -1 can be an immediate or in a register.

On arm64, there are no exceptions:
  - LLONG_MIN/-1 = LLONG_MIN
  - INT_MIN/-1 = INT_MIN
  - LLONG_MIN%-1 = 0
  - INT_MIN%-1 = 0
where -1 can be an immediate or in a register.

Insn patching is needed to handle the above cases and the patched codes
produced results aligned with above arm64 result. The below are pseudo
codes to handle sdiv/smod exceptions including both divisor -1 and divisor 0
and the divisor is stored in a register.

sdiv:
      tmp = rX
      tmp += 1 /* [-1, 0] -> [0, 1]
      if tmp >(unsigned) 1 goto L2
      if tmp == 0 goto L1
      rY = 0
  L1:
      rY = -rY;
      goto L3
  L2:
      rY /= rX
  L3:

smod:
      tmp = rX
      tmp += 1 /* [-1, 0] -> [0, 1]
      if tmp >(unsigned) 1 goto L1
      if tmp == 1 (is64 ? goto L2 : goto L3)
      rY = 0;
      goto L2
  L1:
      rY %= rX
  L2:
      goto L4  // only when !is64
  L3:
      wY = wY  // only when !is64
  L4:

  [1] https://lore.kernel.org/bpf/tPJLTEh7S_DxFEqAI2Ji5MBSoZVg7_G-Py2iaZpAaWtM961fFTWtsnlzwvTbzBzaUzwQAoNATXKUlt0LZOFgnDcIyKCswAnAGdUF3LBrhGQ=@protonmail.com/



Reported-by: default avatarZac Ecob <zacecob@protonmail.com>
Closes: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4902a6a0dc593c82055fc8c9ada371bafe26c9cc


Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240913150326.1187788-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Conflicts:
	kernel/bpf/verifier.c
[The conflicts were due to not merge the commits 74a7e76f, c3a02b06]
Signed-off-by: default avatarXiaomeng Zhang <zhangxiaomeng13@huawei.com>
parent 442847ce

kernel/bpf/verifier.c

+89 −4
Original line number Diff line number Diff line
@@ -18905,13 +18905,46 @@ static int do_misc_fixups(struct bpf_verifier_env *env) 
	int i, ret, cnt, delta = 0;









	for (i = 0; i < insn_cnt; i++, insn++) {









		/* Make divide-by-zero exceptions impossible. */









		/* Make sdiv/smod divide-by-minus-one exceptions impossible. */









		if ((insn->code == (BPF_ALU64 | BPF_MOD | BPF_K) ||









		     insn->code == (BPF_ALU64 | BPF_DIV | BPF_K) ||









		     insn->code == (BPF_ALU | BPF_MOD | BPF_K) ||









		     insn->code == (BPF_ALU | BPF_DIV | BPF_K)) &&









		    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),









			};

















			patchlet = isdiv ? chk_and_sdiv : chk_and_smod;









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

















			new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt);









			if (!new_prog)









				return -ENOMEM;

















			delta    += cnt - 1;









			env->prog = prog = new_prog;









			insn      = new_prog->insnsi + i + delta;









			continue;









		}

















		/* Make divide-by-zero and divide-by-minus-one exceptions impossible. */









		if (insn->code == (BPF_ALU64 | BPF_MOD | BPF_X) ||









		    insn->code == (BPF_ALU64 | BPF_DIV | BPF_X) ||









		    insn->code == (BPF_ALU | BPF_MOD | BPF_X) ||









		    insn->code == (BPF_ALU | BPF_DIV | BPF_X)) {









			bool is64 = BPF_CLASS(insn->code) == BPF_ALU64;









			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 */








@@ -18931,10 +18964,62 @@ static int do_misc_fixups(struct bpf_verifier_env *env)







				BPF_JMP_IMM(BPF_JA, 0, 0, 1),









				BPF_MOV32_REG(insn->dst_reg, insn->dst_reg),









			};









			struct bpf_insn chk_and_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),









				/* 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[] = {









				/* [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),









			};

















			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);









			} else {









				patchlet = isdiv ? chk_and_div : chk_and_mod;









				cnt = isdiv ? ARRAY_SIZE(chk_and_div) :









					      ARRAY_SIZE(chk_and_mod) - (is64 ? 2 : 0);









			}

















			new_prog = bpf_patch_insn_data(env, i + delta, patchlet, cnt);









			if (!new_prog)