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, 464 insertions, 0 deletions

diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
new file mode 100644
index 000000000..06d8f78b7
--- /dev/null
+++ b/net/sched/act_bpf.c
@@ -0,0 +1,464 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2015 Jiri Pirko <jiri@resnulli.us>
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/rtnetlink.h>
+#include <linux/filter.h>
+#include <linux/bpf.h>
+
+#include <net/netlink.h>
+#include <net/sock.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+
+#include <linux/tc_act/tc_bpf.h>
+#include <net/tc_act/tc_bpf.h>
+#include <net/tc_wrapper.h>
+
+#define ACT_BPF_NAME_LEN	256
+
+struct tcf_bpf_cfg {
+	struct bpf_prog *filter;
+	struct sock_filter *bpf_ops;
+	const char *bpf_name;
+	u16 bpf_num_ops;
+	bool is_ebpf;
+};
+
+static struct tc_action_ops act_bpf_ops;
+
+TC_INDIRECT_SCOPE int tcf_bpf_act(struct sk_buff *skb,
+				  const struct tc_action *act,
+				  struct tcf_result *res)
+{
+	bool at_ingress = skb_at_tc_ingress(skb);
+	struct tcf_bpf *prog = to_bpf(act);
+	struct bpf_prog *filter;
+	int action, filter_res;
+
+	tcf_lastuse_update(&prog->tcf_tm);
+	bstats_update(this_cpu_ptr(prog->common.cpu_bstats), skb);
+
+	filter = rcu_dereference_bh(prog->filter);
+	if (at_ingress) {
+		__skb_push(skb, skb->mac_len);
+		filter_res = bpf_prog_run_data_pointers(filter, skb);
+		__skb_pull(skb, skb->mac_len);
+	} else {
+		filter_res = bpf_prog_run_data_pointers(filter, skb);
+	}
+	if (unlikely(!skb->tstamp && skb->tstamp_type))
+		skb->tstamp_type = SKB_CLOCK_REALTIME;
+	if (skb_sk_is_prefetched(skb) && filter_res != TC_ACT_OK)
+		skb_orphan(skb);
+
+	/* A BPF program may overwrite the default action opcode.
+	 * Similarly as in cls_bpf, if filter_res == -1 we use the
+	 * default action specified from tc.
+	 *
+	 * In case a different well-known TC_ACT opcode has been
+	 * returned, it will overwrite the default one.
+	 *
+	 * For everything else that is unknown, TC_ACT_UNSPEC is
+	 * returned.
+	 */
+	switch (filter_res) {
+	case TC_ACT_PIPE:
+	case TC_ACT_RECLASSIFY:
+	case TC_ACT_OK:
+	case TC_ACT_REDIRECT:
+		action = filter_res;
+		break;
+	case TC_ACT_SHOT:
+		action = filter_res;
+		qstats_cpu_drop_inc(prog->common.cpu_qstats);
+		break;
+	case TC_ACT_UNSPEC:
+		action = prog->tcf_action;
+		break;
+	default:
+		action = TC_ACT_UNSPEC;
+		break;
+	}
+
+	return action;
+}
+
+static bool tcf_bpf_is_ebpf(const struct tcf_bpf *prog)
+{
+	return !prog->bpf_ops;
+}
+
+static int tcf_bpf_dump_bpf_info(const struct tcf_bpf *prog,
+				 struct sk_buff *skb)
+{
+	struct nlattr *nla;
+
+	if (nla_put_u16(skb, TCA_ACT_BPF_OPS_LEN, prog->bpf_num_ops))
+		return -EMSGSIZE;
+
+	nla = nla_reserve(skb, TCA_ACT_BPF_OPS, prog->bpf_num_ops *
+			  sizeof(struct sock_filter));
+	if (nla == NULL)
+		return -EMSGSIZE;
+
+	memcpy(nla_data(nla), prog->bpf_ops, nla_len(nla));
+
+	return 0;
+}
+
+static int tcf_bpf_dump_ebpf_info(const struct tcf_bpf *prog,
+				  struct sk_buff *skb)
+{
+	struct nlattr *nla;
+
+	if (prog->bpf_name &&
+	    nla_put_string(skb, TCA_ACT_BPF_NAME, prog->bpf_name))
+		return -EMSGSIZE;
+
+	if (nla_put_u32(skb, TCA_ACT_BPF_ID, prog->filter->aux->id))
+		return -EMSGSIZE;
+
+	nla = nla_reserve(skb, TCA_ACT_BPF_TAG, sizeof(prog->filter->tag));
+	if (nla == NULL)
+		return -EMSGSIZE;
+
+	memcpy(nla_data(nla), prog->filter->tag, nla_len(nla));
+
+	return 0;
+}
+
+static int tcf_bpf_dump(struct sk_buff *skb, struct tc_action *act,
+			int bind, int ref)
+{
+	unsigned char *tp = skb_tail_pointer(skb);
+	struct tcf_bpf *prog = to_bpf(act);
+	struct tc_act_bpf opt = {
+		.index   = prog->tcf_index,
+		.refcnt  = refcount_read(&prog->tcf_refcnt) - ref,
+		.bindcnt = atomic_read(&prog->tcf_bindcnt) - bind,
+	};
+	struct tcf_t tm;
+	int ret;
+
+	spin_lock_bh(&prog->tcf_lock);
+	opt.action = prog->tcf_action;
+	if (nla_put(skb, TCA_ACT_BPF_PARMS, sizeof(opt), &opt))
+		goto nla_put_failure;
+
+	if (tcf_bpf_is_ebpf(prog))
+		ret = tcf_bpf_dump_ebpf_info(prog, skb);
+	else
+		ret = tcf_bpf_dump_bpf_info(prog, skb);
+	if (ret)
+		goto nla_put_failure;
+
+	tcf_tm_dump(&tm, &prog->tcf_tm);
+	if (nla_put_64bit(skb, TCA_ACT_BPF_TM, sizeof(tm), &tm,
+			  TCA_ACT_BPF_PAD))
+		goto nla_put_failure;
+
+	spin_unlock_bh(&prog->tcf_lock);
+	return skb->len;
+
+nla_put_failure:
+	spin_unlock_bh(&prog->tcf_lock);
+	nlmsg_trim(skb, tp);
+	return -1;
+}
+
+static const struct nla_policy act_bpf_policy[TCA_ACT_BPF_MAX + 1] = {
+	[TCA_ACT_BPF_PARMS]	= { .len = sizeof(struct tc_act_bpf) },
+	[TCA_ACT_BPF_FD]	= { .type = NLA_U32 },
+	[TCA_ACT_BPF_NAME]	= { .type = NLA_NUL_STRING,
+				    .len = ACT_BPF_NAME_LEN },
+	[TCA_ACT_BPF_OPS_LEN]	= { .type = NLA_U16 },
+	[TCA_ACT_BPF_OPS]	= { .type = NLA_BINARY,
+				    .len = sizeof(struct sock_filter) * BPF_MAXINSNS },
+};
+
+static int tcf_bpf_init_from_ops(struct nlattr **tb, struct tcf_bpf_cfg *cfg)
+{
+	struct sock_filter *bpf_ops;
+	struct sock_fprog_kern fprog_tmp;
+	struct bpf_prog *fp;
+	u16 bpf_size, bpf_num_ops;
+	int ret;
+
+	bpf_num_ops = nla_get_u16(tb[TCA_ACT_BPF_OPS_LEN]);
+	if (bpf_num_ops	> BPF_MAXINSNS || bpf_num_ops == 0)
+		return -EINVAL;
+
+	bpf_size = bpf_num_ops * sizeof(*bpf_ops);
+	if (bpf_size != nla_len(tb[TCA_ACT_BPF_OPS]))
+		return -EINVAL;
+
+	bpf_ops = kmemdup(nla_data(tb[TCA_ACT_BPF_OPS]), bpf_size, GFP_KERNEL);
+	if (bpf_ops == NULL)
+		return -ENOMEM;
+
+	fprog_tmp.len = bpf_num_ops;
+	fprog_tmp.filter = bpf_ops;
+
+	ret = bpf_prog_create(&fp, &fprog_tmp);
+	if (ret < 0) {
+		kfree(bpf_ops);
+		return ret;
+	}
+
+	cfg->bpf_ops = bpf_ops;
+	cfg->bpf_num_ops = bpf_num_ops;
+	cfg->filter = fp;
+	cfg->is_ebpf = false;
+
+	return 0;
+}
+
+static int tcf_bpf_init_from_efd(struct nlattr **tb, struct tcf_bpf_cfg *cfg)
+{
+	struct bpf_prog *fp;
+	char *name = NULL;
+	u32 bpf_fd;
+
+	bpf_fd = nla_get_u32(tb[TCA_ACT_BPF_FD]);
+
+	fp = bpf_prog_get_type(bpf_fd, BPF_PROG_TYPE_SCHED_ACT);
+	if (IS_ERR(fp))
+		return PTR_ERR(fp);
+
+	if (tb[TCA_ACT_BPF_NAME]) {
+		name = nla_memdup(tb[TCA_ACT_BPF_NAME], GFP_KERNEL);
+		if (!name) {
+			bpf_prog_put(fp);
+			return -ENOMEM;
+		}
+	}
+
+	cfg->bpf_name = name;
+	cfg->filter = fp;
+	cfg->is_ebpf = true;
+
+	return 0;
+}
+
+static void tcf_bpf_cfg_cleanup(const struct tcf_bpf_cfg *cfg)
+{
+	struct bpf_prog *filter = cfg->filter;
+
+	if (filter) {
+		if (cfg->is_ebpf)
+			bpf_prog_put(filter);
+		else
+			bpf_prog_destroy(filter);
+	}
+
+	kfree(cfg->bpf_ops);
+	kfree(cfg->bpf_name);
+}
+
+static void tcf_bpf_prog_fill_cfg(const struct tcf_bpf *prog,
+				  struct tcf_bpf_cfg *cfg)
+{
+	cfg->is_ebpf = tcf_bpf_is_ebpf(prog);
+	/* updates to prog->filter are prevented, since it's called either
+	 * with tcf lock or during final cleanup in rcu callback
+	 */
+	cfg->filter = rcu_dereference_protected(prog->filter, 1);
+
+	cfg->bpf_ops = prog->bpf_ops;
+	cfg->bpf_name = prog->bpf_name;
+}
+
+static int tcf_bpf_init(struct net *net, struct nlattr *nla,
+			struct nlattr *est, struct tc_action **act,
+			struct tcf_proto *tp, u32 flags,
+			struct netlink_ext_ack *extack)
+{
+	struct tc_action_net *tn = net_generic(net, act_bpf_ops.net_id);
+	bool bind = flags & TCA_ACT_FLAGS_BIND;
+	struct nlattr *tb[TCA_ACT_BPF_MAX + 1];
+	struct tcf_chain *goto_ch = NULL;
+	struct tcf_bpf_cfg cfg, old;
+	struct tc_act_bpf *parm;
+	struct tcf_bpf *prog;
+	bool is_bpf, is_ebpf;
+	int ret, res = 0;
+	u32 index;
+
+	if (!nla)
+		return -EINVAL;
+
+	ret = nla_parse_nested_deprecated(tb, TCA_ACT_BPF_MAX, nla,
+					  act_bpf_policy, NULL);
+	if (ret < 0)
+		return ret;
+
+	if (!tb[TCA_ACT_BPF_PARMS])
+		return -EINVAL;
+
+	parm = nla_data(tb[TCA_ACT_BPF_PARMS]);
+	index = parm->index;
+	ret = tcf_idr_check_alloc(tn, &index, act, bind);
+	if (!ret) {
+		ret = tcf_idr_create(tn, index, est, act,
+				     &act_bpf_ops, bind, true, flags);
+		if (ret < 0) {
+			tcf_idr_cleanup(tn, index);
+			return ret;
+		}
+
+		res = ACT_P_CREATED;
+	} else if (ret > 0) {
+		/* Don't override defaults. */
+		if (bind)
+			return ACT_P_BOUND;
+
+		if (!(flags & TCA_ACT_FLAGS_REPLACE)) {
+			tcf_idr_release(*act, bind);
+			return -EEXIST;
+		}
+	} else {
+		return ret;
+	}
+
+	ret = tcf_action_check_ctrlact(parm->action, tp, &goto_ch, extack);
+	if (ret < 0)
+		goto release_idr;
+
+	is_bpf = tb[TCA_ACT_BPF_OPS_LEN] && tb[TCA_ACT_BPF_OPS];
+	is_ebpf = tb[TCA_ACT_BPF_FD];
+
+	if (is_bpf == is_ebpf) {
+		ret = -EINVAL;
+		goto put_chain;
+	}
+
+	memset(&cfg, 0, sizeof(cfg));
+
+	ret = is_bpf ? tcf_bpf_init_from_ops(tb, &cfg) :
+		       tcf_bpf_init_from_efd(tb, &cfg);
+	if (ret < 0)
+		goto put_chain;
+
+	prog = to_bpf(*act);
+
+	spin_lock_bh(&prog->tcf_lock);
+	if (res != ACT_P_CREATED)
+		tcf_bpf_prog_fill_cfg(prog, &old);
+
+	prog->bpf_ops = cfg.bpf_ops;
+	prog->bpf_name = cfg.bpf_name;
+
+	if (cfg.bpf_num_ops)
+		prog->bpf_num_ops = cfg.bpf_num_ops;
+
+	goto_ch = tcf_action_set_ctrlact(*act, parm->action, goto_ch);
+	rcu_assign_pointer(prog->filter, cfg.filter);
+	spin_unlock_bh(&prog->tcf_lock);
+
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+
+	if (res != ACT_P_CREATED) {
+		/* make sure the program being replaced is no longer executing */
+		synchronize_rcu();
+		tcf_bpf_cfg_cleanup(&old);
+	}
+
+	return res;
+
+put_chain:
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+
+release_idr:
+	tcf_idr_release(*act, bind);
+	return ret;
+}
+
+static void tcf_bpf_cleanup(struct tc_action *act)
+{
+	struct tcf_bpf_cfg tmp;
+
+	tcf_bpf_prog_fill_cfg(to_bpf(act), &tmp);
+	tcf_bpf_cfg_cleanup(&tmp);
+}
+
+static size_t tcf_bpf_get_fill_size(const struct tc_action *act)
+{
+	struct tcf_bpf *prog = to_bpf(act);
+	size_t size = nla_total_size(sizeof(struct tc_act_bpf));
+
+	/* bpf_ops and bpf_num_ops are published as separate stores under
+	 * tcf_lock, so take it here as tcf_bpf_dump() does.
+	 */
+	spin_lock_bh(&prog->tcf_lock);
+	if (tcf_bpf_is_ebpf(prog)) {
+		/* TCA_ACT_BPF_NAME */
+		size += nla_total_size(ACT_BPF_NAME_LEN + 1);
+		size += nla_total_size(sizeof(u32)); /* TCA_ACT_BPF_ID */
+		size += nla_total_size(BPF_TAG_SIZE); /* TCA_ACT_BPF_TAG */
+	} else {
+		size += nla_total_size(sizeof(u16)); /* TCA_ACT_BPF_OPS_LEN */
+		/* TCA_ACT_BPF_OPS */
+		size += nla_total_size(prog->bpf_num_ops *
+				       sizeof(struct sock_filter));
+	}
+	spin_unlock_bh(&prog->tcf_lock);
+
+	return size;
+}
+
+static struct tc_action_ops act_bpf_ops __read_mostly = {
+	.kind		=	"bpf",
+	.id		=	TCA_ID_BPF,
+	.owner		=	THIS_MODULE,
+	.act		=	tcf_bpf_act,
+	.dump		=	tcf_bpf_dump,
+	.cleanup	=	tcf_bpf_cleanup,
+	.init		=	tcf_bpf_init,
+	.get_fill_size	=	tcf_bpf_get_fill_size,
+	.size		=	sizeof(struct tcf_bpf),
+};
+MODULE_ALIAS_NET_ACT("bpf");
+
+static __net_init int bpf_init_net(struct net *net)
+{
+	struct tc_action_net *tn = net_generic(net, act_bpf_ops.net_id);
+
+	return tc_action_net_init(net, tn, &act_bpf_ops);
+}
+
+static void __net_exit bpf_exit_net(struct list_head *net_list)
+{
+	tc_action_net_exit(net_list, act_bpf_ops.net_id);
+}
+
+static struct pernet_operations bpf_net_ops = {
+	.init = bpf_init_net,
+	.exit_batch = bpf_exit_net,
+	.id   = &act_bpf_ops.net_id,
+	.size = sizeof(struct tc_action_net),
+};
+
+static int __init bpf_init_module(void)
+{
+	return tcf_register_action(&act_bpf_ops, &bpf_net_ops);
+}
+
+static void __exit bpf_cleanup_module(void)
+{
+	tcf_unregister_action(&act_bpf_ops, &bpf_net_ops);
+}
+
+module_init(bpf_init_module);
+module_exit(bpf_cleanup_module);
+
+MODULE_AUTHOR("Jiri Pirko <jiri@resnulli.us>");
+MODULE_DESCRIPTION("TC BPF based action");
+MODULE_LICENSE("GPL v2");