From b3b50f05dc501cc2cd90349a7bbfd932af0ceb31 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 8 Jul 2019 20:32:44 -0700 Subject: [PATCH] bpf: fix precision bit propagation for BPF_ST instructions When backtracking instructions to propagate precision bit for registers and stack slots, one class of instructions (BPF_ST) weren't handled causing extra stack slots to be propagated into parent state. Parent state might not have that much stack allocated, though, which causes warning on invalid stack slot usage. This patch adds handling of BPF_ST instructions: BPF_MEM | | BPF_ST: *(size *) (dst_reg + off) = imm32 Reported-by: syzbot+4da3ff23081bafe74fc2@syzkaller.appspotmail.com Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking") Cc: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a2e763703c30..def87e9cc9c7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1519,9 +1519,9 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, return -EFAULT; } *stack_mask |= 1ull << spi; - } else if (class == BPF_STX) { + } else if (class == BPF_STX || class == BPF_ST) { if (*reg_mask & dreg) - /* stx shouldn't be using _scalar_ dst_reg + /* stx & st shouldn't be using _scalar_ dst_reg * to access memory. It means backtracking * encountered a case of pointer subtraction. */ @@ -1540,7 +1540,8 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, if (!(*stack_mask & (1ull << spi))) return 0; *stack_mask &= ~(1ull << spi); - *reg_mask |= sreg; + if (class == BPF_STX) + *reg_mask |= sreg; } else if (class == BPF_JMP || class == BPF_JMP32) { if (opcode == BPF_CALL) { if (insn->src_reg == BPF_PSEUDO_CALL) @@ -1569,10 +1570,6 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, if (mode == BPF_IND || mode == BPF_ABS) /* to be analyzed */ return -ENOTSUPP; - } else if (class == BPF_ST) { - if (*reg_mask & dreg) - /* likely pointer subtraction */ - return -ENOTSUPP; } return 0; } -- 2.30.2