x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 393 insertions, 0 deletions

diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h
new file mode 100644
index 000000000..8aca88193
--- /dev/null
+++ b/include/net/fq_impl.h
@@ -0,0 +1,393 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2016 Qualcomm Atheros, Inc
+ *
+ * Based on net/sched/sch_fq_codel.c
+ */
+#ifndef __NET_SCHED_FQ_IMPL_H
+#define __NET_SCHED_FQ_IMPL_H
+
+#include <net/fq.h>
+
+/* functions that are embedded into includer */
+
+
+static void
+__fq_adjust_removal(struct fq *fq, struct fq_flow *flow, unsigned int packets,
+		    unsigned int bytes, unsigned int truesize)
+{
+	struct fq_tin *tin = flow->tin;
+	int idx;
+
+	tin->backlog_bytes -= bytes;
+	tin->backlog_packets -= packets;
+	flow->backlog -= bytes;
+	fq->backlog -= packets;
+	fq->memory_usage -= truesize;
+
+	if (flow->backlog)
+		return;
+
+	if (flow == &tin->default_flow) {
+		list_del_init(&tin->tin_list);
+		return;
+	}
+
+	idx = flow - fq->flows;
+	__clear_bit(idx, fq->flows_bitmap);
+}
+
+static void fq_adjust_removal(struct fq *fq,
+			      struct fq_flow *flow,
+			      struct sk_buff *skb)
+{
+	__fq_adjust_removal(fq, flow, 1, skb->len, skb->truesize);
+}
+
+static struct sk_buff *fq_flow_dequeue(struct fq *fq,
+				       struct fq_flow *flow)
+{
+	struct sk_buff *skb;
+
+	lockdep_assert_held(&fq->lock);
+
+	skb = __skb_dequeue(&flow->queue);
+	if (!skb)
+		return NULL;
+
+	fq_adjust_removal(fq, flow, skb);
+
+	return skb;
+}
+
+static int fq_flow_drop(struct fq *fq, struct fq_flow *flow,
+			fq_skb_free_t free_func)
+{
+	unsigned int packets = 0, bytes = 0, truesize = 0;
+	struct fq_tin *tin = flow->tin;
+	struct sk_buff *skb;
+	int pending;
+
+	lockdep_assert_held(&fq->lock);
+
+	pending = min_t(int, 32, skb_queue_len(&flow->queue) / 2);
+	do {
+		skb = __skb_dequeue(&flow->queue);
+		if (!skb)
+			break;
+
+		packets++;
+		bytes += skb->len;
+		truesize += skb->truesize;
+		free_func(fq, tin, flow, skb);
+	} while (packets < pending);
+
+	__fq_adjust_removal(fq, flow, packets, bytes, truesize);
+
+	return packets;
+}
+
+static struct sk_buff *fq_tin_dequeue(struct fq *fq,
+				      struct fq_tin *tin,
+				      fq_tin_dequeue_t dequeue_func)
+{
+	struct fq_flow *flow;
+	struct list_head *head;
+	struct sk_buff *skb;
+
+	lockdep_assert_held(&fq->lock);
+
+begin:
+	head = &tin->new_flows;
+	if (list_empty(head)) {
+		head = &tin->old_flows;
+		if (list_empty(head))
+			return NULL;
+	}
+
+	flow = list_first_entry(head, struct fq_flow, flowchain);
+
+	if (flow->deficit <= 0) {
+		flow->deficit += fq->quantum;
+		list_move_tail(&flow->flowchain,
+			       &tin->old_flows);
+		goto begin;
+	}
+
+	skb = dequeue_func(fq, tin, flow);
+	if (!skb) {
+		/* force a pass through old_flows to prevent starvation */
+		if ((head == &tin->new_flows) &&
+		    !list_empty(&tin->old_flows)) {
+			list_move_tail(&flow->flowchain, &tin->old_flows);
+		} else {
+			list_del_init(&flow->flowchain);
+			flow->tin = NULL;
+		}
+		goto begin;
+	}
+
+	flow->deficit -= skb->len;
+	tin->tx_bytes += skb->len;
+	tin->tx_packets++;
+
+	return skb;
+}
+
+static u32 fq_flow_idx(struct fq *fq, struct sk_buff *skb)
+{
+	u32 hash = skb_get_hash(skb);
+
+	return reciprocal_scale(hash, fq->flows_cnt);
+}
+
+static struct fq_flow *fq_flow_classify(struct fq *fq,
+					struct fq_tin *tin, u32 idx,
+					struct sk_buff *skb)
+{
+	struct fq_flow *flow;
+
+	lockdep_assert_held(&fq->lock);
+
+	flow = &fq->flows[idx];
+	if (flow->tin && flow->tin != tin) {
+		flow = &tin->default_flow;
+		tin->collisions++;
+		fq->collisions++;
+	}
+
+	if (!flow->tin)
+		tin->flows++;
+
+	return flow;
+}
+
+static struct fq_flow *fq_find_fattest_flow(struct fq *fq)
+{
+	struct fq_tin *tin;
+	struct fq_flow *flow = NULL;
+	u32 len = 0;
+	int i;
+
+	for_each_set_bit(i, fq->flows_bitmap, fq->flows_cnt) {
+		struct fq_flow *cur = &fq->flows[i];
+		unsigned int cur_len;
+
+		cur_len = cur->backlog;
+		if (cur_len <= len)
+			continue;
+
+		flow = cur;
+		len = cur_len;
+	}
+
+	list_for_each_entry(tin, &fq->tin_backlog, tin_list) {
+		unsigned int cur_len = tin->default_flow.backlog;
+
+		if (cur_len <= len)
+			continue;
+
+		flow = &tin->default_flow;
+		len = cur_len;
+	}
+
+	return flow;
+}
+
+static void fq_tin_enqueue(struct fq *fq,
+			   struct fq_tin *tin, u32 idx,
+			   struct sk_buff *skb,
+			   fq_skb_free_t free_func)
+{
+	struct fq_flow *flow;
+	struct sk_buff *next;
+	bool oom;
+
+	lockdep_assert_held(&fq->lock);
+
+	flow = fq_flow_classify(fq, tin, idx, skb);
+
+	if (!flow->backlog) {
+		if (flow != &tin->default_flow)
+			__set_bit(idx, fq->flows_bitmap);
+		else if (list_empty(&tin->tin_list))
+			list_add(&tin->tin_list, &fq->tin_backlog);
+	}
+
+	flow->tin = tin;
+	skb_list_walk_safe(skb, skb, next) {
+		skb_mark_not_on_list(skb);
+		flow->backlog += skb->len;
+		tin->backlog_bytes += skb->len;
+		tin->backlog_packets++;
+		fq->memory_usage += skb->truesize;
+		fq->backlog++;
+		__skb_queue_tail(&flow->queue, skb);
+	}
+
+	if (list_empty(&flow->flowchain)) {
+		flow->deficit = fq->quantum;
+		list_add_tail(&flow->flowchain,
+			      &tin->new_flows);
+	}
+
+	oom = (fq->memory_usage > fq->memory_limit);
+	while (fq->backlog > fq->limit || oom) {
+		flow = fq_find_fattest_flow(fq);
+		if (!flow)
+			return;
+
+		if (!fq_flow_drop(fq, flow, free_func))
+			return;
+
+		flow->tin->overlimit++;
+		fq->overlimit++;
+		if (oom) {
+			fq->overmemory++;
+			oom = (fq->memory_usage > fq->memory_limit);
+		}
+	}
+}
+
+static void fq_flow_filter(struct fq *fq,
+			   struct fq_flow *flow,
+			   fq_skb_filter_t filter_func,
+			   void *filter_data,
+			   fq_skb_free_t free_func)
+{
+	struct fq_tin *tin = flow->tin;
+	struct sk_buff *skb, *tmp;
+
+	lockdep_assert_held(&fq->lock);
+
+	skb_queue_walk_safe(&flow->queue, skb, tmp) {
+		if (!filter_func(fq, tin, flow, skb, filter_data))
+			continue;
+
+		__skb_unlink(skb, &flow->queue);
+		fq_adjust_removal(fq, flow, skb);
+		free_func(fq, tin, flow, skb);
+	}
+}
+
+static void fq_tin_filter(struct fq *fq,
+			  struct fq_tin *tin,
+			  fq_skb_filter_t filter_func,
+			  void *filter_data,
+			  fq_skb_free_t free_func)
+{
+	struct fq_flow *flow;
+
+	lockdep_assert_held(&fq->lock);
+
+	list_for_each_entry(flow, &tin->new_flows, flowchain)
+		fq_flow_filter(fq, flow, filter_func, filter_data, free_func);
+	list_for_each_entry(flow, &tin->old_flows, flowchain)
+		fq_flow_filter(fq, flow, filter_func, filter_data, free_func);
+}
+
+static void fq_flow_reset(struct fq *fq,
+			  struct fq_flow *flow,
+			  fq_skb_free_t free_func)
+{
+	struct fq_tin *tin = flow->tin;
+	struct sk_buff *skb;
+
+	while ((skb = fq_flow_dequeue(fq, flow)))
+		free_func(fq, tin, flow, skb);
+
+	if (!list_empty(&flow->flowchain)) {
+		list_del_init(&flow->flowchain);
+		if (list_empty(&tin->new_flows) &&
+		    list_empty(&tin->old_flows))
+			list_del_init(&tin->tin_list);
+	}
+
+	flow->tin = NULL;
+
+	WARN_ON_ONCE(flow->backlog);
+}
+
+static void fq_tin_reset(struct fq *fq,
+			 struct fq_tin *tin,
+			 fq_skb_free_t free_func)
+{
+	struct list_head *head;
+	struct fq_flow *flow;
+
+	for (;;) {
+		head = &tin->new_flows;
+		if (list_empty(head)) {
+			head = &tin->old_flows;
+			if (list_empty(head))
+				break;
+		}
+
+		flow = list_first_entry(head, struct fq_flow, flowchain);
+		fq_flow_reset(fq, flow, free_func);
+	}
+
+	WARN_ON_ONCE(!list_empty(&tin->tin_list));
+	WARN_ON_ONCE(tin->backlog_bytes);
+	WARN_ON_ONCE(tin->backlog_packets);
+}
+
+static void fq_flow_init(struct fq_flow *flow)
+{
+	INIT_LIST_HEAD(&flow->flowchain);
+	__skb_queue_head_init(&flow->queue);
+}
+
+static void fq_tin_init(struct fq_tin *tin)
+{
+	INIT_LIST_HEAD(&tin->new_flows);
+	INIT_LIST_HEAD(&tin->old_flows);
+	INIT_LIST_HEAD(&tin->tin_list);
+	fq_flow_init(&tin->default_flow);
+}
+
+static int fq_init(struct fq *fq, int flows_cnt)
+{
+	int i;
+
+	memset(fq, 0, sizeof(fq[0]));
+	spin_lock_init(&fq->lock);
+	INIT_LIST_HEAD(&fq->tin_backlog);
+	fq->flows_cnt = max_t(u32, flows_cnt, 1);
+	fq->quantum = 300;
+	fq->limit = 8192;
+	fq->memory_limit = 16 << 20; /* 16 MBytes */
+
+	fq->flows = kvzalloc_objs(fq->flows[0], fq->flows_cnt);
+	if (!fq->flows)
+		return -ENOMEM;
+
+	fq->flows_bitmap = bitmap_zalloc(fq->flows_cnt, GFP_KERNEL);
+	if (!fq->flows_bitmap) {
+		kvfree(fq->flows);
+		fq->flows = NULL;
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < fq->flows_cnt; i++)
+		fq_flow_init(&fq->flows[i]);
+
+	return 0;
+}
+
+static void fq_reset(struct fq *fq,
+		     fq_skb_free_t free_func)
+{
+	int i;
+
+	for (i = 0; i < fq->flows_cnt; i++)
+		fq_flow_reset(fq, &fq->flows[i], free_func);
+
+	kvfree(fq->flows);
+	fq->flows = NULL;
+
+	bitmap_free(fq->flows_bitmap);
+	fq->flows_bitmap = NULL;
+}
+
+#endif