From b3b50f05dc501cc2cd90349a7bbfd932af0ceb31 Mon Sep 17 00:00:00 2001
From: Andrii Nakryiko <andriin@fb.com>
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 | <size> | BPF_ST: *(size *) (dst_reg + off) = imm32
Reported-by: syzbot+4da3ff23081bafe74fc2@syzkaller.appspotmail.com
Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking")
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
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 a2e763703c300..def87e9cc9c79 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;
}
--
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