2024-03-14 17:49:47

by Puranjay Mohan

Subject: [PATCH bpf] bpf: Temporarily disable atomic operations in BPF arena

Currently, the x86 JIT handling PROBE_MEM32 tagged accesses is not
equipped to handle atomic accesses into PTR_TO_ARENA, as no PROBE_MEM32
tagging is performed and no handling is enabled for them.

This will lead to unsafety as the offset into arena will dereferenced
directly without turning it into a base + offset access into the arena
region.

Since the changes to the x86 JIT will be fairly involved, for now,
temporarily disallow use of PTR_TO_ARENA as the destination operand for
atomics until support is added to the JIT backend.

Fixes: 2fe99eb0ccf2 ("bpf: Add x86-64 JIT support for PROBE_MEM32 pseudo instructions.")
Reported-by: Kumar Kartikeya Dwivedi <[email protected]>
Signed-off-by: Puranjay Mohan <[email protected]>
Acked-by: Kumar Kartikeya Dwivedi <[email protected]>
---
kernel/bpf/verifier.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 63749ad5ac6b..1dd3b99d1bb9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5682,6 +5682,13 @@ static bool is_flow_key_reg(struct bpf_verifier_env *env, int regno)
return reg->type == PTR_TO_FLOW_KEYS;
}

+static bool is_arena_reg(struct bpf_verifier_env *env, int regno)
+{
+ const struct bpf_reg_state *reg = reg_state(env, regno);
+
+ return reg->type == PTR_TO_ARENA;
+}
+
static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = {
#ifdef CONFIG_NET
[PTR_TO_SOCKET] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK],
@@ -7019,7 +7026,8 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
if (is_ctx_reg(env, insn->dst_reg) ||
is_pkt_reg(env, insn->dst_reg) ||
is_flow_key_reg(env, insn->dst_reg) ||
- is_sk_reg(env, insn->dst_reg)) {
+ is_sk_reg(env, insn->dst_reg) ||
+ is_arena_reg(env, insn->dst_reg)) {
verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
insn->dst_reg,
reg_type_str(env, reg_state(env, insn->dst_reg)->type));
--
2.40.1

2024-03-14 19:10:42

by patchwork-bot+netdevbpf

Subject: Re: [PATCH bpf] bpf: Temporarily disable atomic operations in BPF arena

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <[email protected]>:

On Thu, 14 Mar 2024 17:49:31 +0000 you wrote:
> Currently, the x86 JIT handling PROBE_MEM32 tagged accesses is not
> equipped to handle atomic accesses into PTR_TO_ARENA, as no PROBE_MEM32
> tagging is performed and no handling is enabled for them.
>
> This will lead to unsafety as the offset into arena will dereferenced
> directly without turning it into a base + offset access into the arena
> region.
>
> [...]

Here is the summary with links:
- [bpf] bpf: Temporarily disable atomic operations in BPF arena
https://git.kernel.org/bpf/bpf/c/44d79142ede8

You are awesome, thank you!
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