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, 664 insertions, 0 deletions

diff --git a/net/tls/tls_strp.c b/net/tls/tls_strp.c
new file mode 100644
index 000000000..6cc222008
--- /dev/null
+++ b/net/tls/tls_strp.c
@@ -0,0 +1,664 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2016 Tom Herbert <tom@herbertland.com> */
+
+#include <linux/skbuff.h>
+#include <linux/skbuff_ref.h>
+#include <linux/workqueue.h>
+#include <net/strparser.h>
+#include <net/tcp.h>
+#include <net/sock.h>
+#include <net/tls.h>
+
+#include "tls.h"
+
+static struct workqueue_struct *tls_strp_wq;
+
+void tls_strp_abort_strp(struct tls_strparser *strp, int err)
+{
+	if (strp->stopped)
+		return;
+
+	strp->stopped = 1;
+
+	/* Report an error on the lower socket */
+	WRITE_ONCE(strp->sk->sk_err, -err);
+	/* Paired with smp_rmb() in tcp_poll() */
+	smp_wmb();
+	sk_error_report(strp->sk);
+}
+
+static void tls_strp_anchor_free(struct tls_strparser *strp)
+{
+	struct skb_shared_info *shinfo = skb_shinfo(strp->anchor);
+
+	DEBUG_NET_WARN_ON_ONCE(atomic_read(&shinfo->dataref) != 1);
+	if (!strp->copy_mode)
+		shinfo->frag_list = NULL;
+	consume_skb(strp->anchor);
+	strp->anchor = NULL;
+}
+
+static struct sk_buff *
+tls_strp_skb_copy(struct tls_strparser *strp, struct sk_buff *in_skb,
+		  int offset, int len)
+{
+	struct sk_buff *skb;
+	int i, err;
+
+	skb = alloc_skb_with_frags(0, len, TLS_PAGE_ORDER,
+				   &err, strp->sk->sk_allocation);
+	if (!skb)
+		return NULL;
+
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+		skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+
+		WARN_ON_ONCE(skb_copy_bits(in_skb, offset,
+					   skb_frag_address(frag),
+					   skb_frag_size(frag)));
+		offset += skb_frag_size(frag);
+	}
+
+	skb->len = len;
+	skb->data_len = len;
+	skb_copy_header(skb, in_skb);
+	return skb;
+}
+
+/* Create a new skb with the contents of input copied to its page frags */
+static struct sk_buff *tls_strp_msg_make_copy(struct tls_strparser *strp)
+{
+	struct strp_msg *rxm;
+	struct sk_buff *skb;
+
+	skb = tls_strp_skb_copy(strp, strp->anchor, strp->stm.offset,
+				strp->stm.full_len);
+	if (!skb)
+		return NULL;
+
+	rxm = strp_msg(skb);
+	rxm->offset = 0;
+	return skb;
+}
+
+/* Steal the input skb, input msg is invalid after calling this function */
+struct sk_buff *tls_strp_msg_detach(struct tls_sw_context_rx *ctx)
+{
+	struct tls_strparser *strp = &ctx->strp;
+
+#ifdef CONFIG_TLS_DEVICE
+	DEBUG_NET_WARN_ON_ONCE(!strp->anchor->decrypted);
+#else
+	/* This function turns an input into an output,
+	 * that can only happen if we have offload.
+	 */
+	WARN_ON(1);
+#endif
+
+	if (strp->copy_mode) {
+		struct sk_buff *skb;
+
+		/* Replace anchor with an empty skb, this is a little
+		 * dangerous but __tls_cur_msg() warns on empty skbs
+		 * so hopefully we'll catch abuses.
+		 */
+		skb = alloc_skb(0, strp->sk->sk_allocation);
+		if (!skb)
+			return NULL;
+
+		swap(strp->anchor, skb);
+		return skb;
+	}
+
+	return tls_strp_msg_make_copy(strp);
+}
+
+/* Force the input skb to be in copy mode. The data ownership remains
+ * with the input skb itself (meaning unpause will wipe it) but it can
+ * be modified.
+ */
+int tls_strp_msg_cow(struct tls_sw_context_rx *ctx)
+{
+	struct tls_strparser *strp = &ctx->strp;
+	struct sk_buff *skb;
+
+	if (strp->copy_mode)
+		return 0;
+
+	skb = tls_strp_msg_make_copy(strp);
+	if (!skb)
+		return -ENOMEM;
+
+	tls_strp_anchor_free(strp);
+	strp->anchor = skb;
+
+	tcp_read_done(strp->sk, strp->stm.full_len);
+	strp->copy_mode = 1;
+
+	return 0;
+}
+
+/* Make a clone (in the skb sense) of the input msg to keep a reference
+ * to the underlying data. The reference-holding skbs get placed on
+ * @dst.
+ */
+int tls_strp_msg_hold(struct tls_strparser *strp, struct sk_buff_head *dst)
+{
+	struct skb_shared_info *shinfo = skb_shinfo(strp->anchor);
+
+	if (strp->copy_mode) {
+		struct sk_buff *skb;
+
+		WARN_ON_ONCE(!shinfo->nr_frags);
+
+		/* We can't skb_clone() the anchor, it gets wiped by unpause */
+		skb = alloc_skb(0, strp->sk->sk_allocation);
+		if (!skb)
+			return -ENOMEM;
+
+		__skb_queue_tail(dst, strp->anchor);
+		strp->anchor = skb;
+	} else {
+		struct sk_buff *iter, *clone;
+		int chunk, len, offset;
+
+		offset = strp->stm.offset;
+		len = strp->stm.full_len;
+		iter = shinfo->frag_list;
+
+		while (len > 0) {
+			if (iter->len <= offset) {
+				offset -= iter->len;
+				goto next;
+			}
+
+			chunk = iter->len - offset;
+			offset = 0;
+
+			clone = skb_clone(iter, strp->sk->sk_allocation);
+			if (!clone)
+				return -ENOMEM;
+			__skb_queue_tail(dst, clone);
+
+			len -= chunk;
+next:
+			iter = iter->next;
+		}
+	}
+
+	return 0;
+}
+
+static void tls_strp_flush_anchor_copy(struct tls_strparser *strp)
+{
+	struct skb_shared_info *shinfo = skb_shinfo(strp->anchor);
+	int i;
+
+	DEBUG_NET_WARN_ON_ONCE(atomic_read(&shinfo->dataref) != 1);
+
+	for (i = 0; i < shinfo->nr_frags; i++)
+		__skb_frag_unref(&shinfo->frags[i], false);
+	shinfo->nr_frags = 0;
+	if (strp->copy_mode) {
+		kfree_skb_list(shinfo->frag_list);
+		shinfo->frag_list = NULL;
+	}
+	strp->copy_mode = 0;
+	strp->mixed_decrypted = 0;
+}
+
+static int tls_strp_copyin_frag(struct tls_strparser *strp, struct sk_buff *skb,
+				struct sk_buff *in_skb, unsigned int offset,
+				size_t in_len)
+{
+	unsigned int nfrag = skb->len / PAGE_SIZE;
+	size_t len, chunk;
+	skb_frag_t *frag;
+	int sz;
+
+	if (unlikely(nfrag >= skb_shinfo(skb)->nr_frags)) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		return -EMSGSIZE;
+	}
+
+	frag = &skb_shinfo(skb)->frags[nfrag];
+
+	len = in_len;
+	/* First make sure we got the header */
+	if (!strp->stm.full_len) {
+		/* Assume one page is more than enough for headers */
+		chunk =	min_t(size_t, len, PAGE_SIZE - skb_frag_size(frag));
+		WARN_ON_ONCE(skb_copy_bits(in_skb, offset,
+					   skb_frag_address(frag) +
+					   skb_frag_size(frag),
+					   chunk));
+
+		skb->len += chunk;
+		skb->data_len += chunk;
+		skb_frag_size_add(frag, chunk);
+
+		sz = tls_rx_msg_size(strp, skb);
+		if (sz < 0)
+			return sz;
+
+		/* We may have over-read, sz == 0 is guaranteed under-read */
+		if (unlikely(sz && sz < skb->len)) {
+			int over = skb->len - sz;
+
+			WARN_ON_ONCE(over > chunk);
+			skb->len -= over;
+			skb->data_len -= over;
+			skb_frag_size_add(frag, -over);
+
+			chunk -= over;
+		}
+
+		frag++;
+		len -= chunk;
+		offset += chunk;
+
+		strp->stm.full_len = sz;
+		if (!strp->stm.full_len)
+			goto read_done;
+	}
+
+	/* Load up more data */
+	while (len && strp->stm.full_len > skb->len) {
+		chunk =	min_t(size_t, len, strp->stm.full_len - skb->len);
+		chunk = min_t(size_t, chunk, PAGE_SIZE - skb_frag_size(frag));
+		WARN_ON_ONCE(skb_copy_bits(in_skb, offset,
+					   skb_frag_address(frag) +
+					   skb_frag_size(frag),
+					   chunk));
+
+		skb->len += chunk;
+		skb->data_len += chunk;
+		skb_frag_size_add(frag, chunk);
+		frag++;
+		len -= chunk;
+		offset += chunk;
+	}
+
+read_done:
+	return in_len - len;
+}
+
+static int tls_strp_copyin_skb(struct tls_strparser *strp, struct sk_buff *skb,
+			       struct sk_buff *in_skb, unsigned int offset,
+			       size_t in_len)
+{
+	struct sk_buff *nskb, *first, *last;
+	struct skb_shared_info *shinfo;
+	size_t chunk;
+	int sz;
+
+	if (strp->stm.full_len)
+		chunk = strp->stm.full_len - skb->len;
+	else
+		chunk = TLS_MAX_PAYLOAD_SIZE + PAGE_SIZE;
+	chunk = min(chunk, in_len);
+
+	nskb = tls_strp_skb_copy(strp, in_skb, offset, chunk);
+	if (!nskb)
+		return -ENOMEM;
+
+	shinfo = skb_shinfo(skb);
+	if (!shinfo->frag_list) {
+		shinfo->frag_list = nskb;
+		nskb->prev = nskb;
+	} else {
+		first = shinfo->frag_list;
+		last = first->prev;
+		last->next = nskb;
+		first->prev = nskb;
+	}
+
+	skb->len += chunk;
+	skb->data_len += chunk;
+
+	if (!strp->stm.full_len) {
+		sz = tls_rx_msg_size(strp, skb);
+		if (sz < 0)
+			return sz;
+
+		/* We may have over-read, sz == 0 is guaranteed under-read */
+		if (unlikely(sz && sz < skb->len)) {
+			int over = skb->len - sz;
+
+			WARN_ON_ONCE(over > chunk);
+			skb->len -= over;
+			skb->data_len -= over;
+			__pskb_trim(nskb, nskb->len - over);
+
+			chunk -= over;
+		}
+
+		strp->stm.full_len = sz;
+	}
+
+	return chunk;
+}
+
+static int tls_strp_copyin(read_descriptor_t *desc, struct sk_buff *in_skb,
+			   unsigned int offset, size_t in_len)
+{
+	struct tls_strparser *strp = (struct tls_strparser *)desc->arg.data;
+	struct sk_buff *skb;
+	int ret;
+
+	if (strp->msg_ready)
+		return 0;
+
+	skb = strp->anchor;
+	if (!skb->len)
+		skb_copy_decrypted(skb, in_skb);
+	else
+		strp->mixed_decrypted |= !!skb_cmp_decrypted(skb, in_skb);
+
+	if (IS_ENABLED(CONFIG_TLS_DEVICE) && strp->mixed_decrypted)
+		ret = tls_strp_copyin_skb(strp, skb, in_skb, offset, in_len);
+	else
+		ret = tls_strp_copyin_frag(strp, skb, in_skb, offset, in_len);
+	if (ret < 0) {
+		desc->error = ret;
+		ret = 0;
+	}
+
+	if (strp->stm.full_len && strp->stm.full_len == skb->len) {
+		desc->count = 0;
+
+		WRITE_ONCE(strp->msg_ready, 1);
+	}
+
+	return ret;
+}
+
+static int tls_strp_read_copyin(struct tls_strparser *strp)
+{
+	read_descriptor_t desc;
+
+	desc.arg.data = strp;
+	desc.error = 0;
+	desc.count = 1; /* give more than one skb per call */
+
+	/* sk should be locked here, so okay to do read_sock */
+	tcp_read_sock(strp->sk, &desc, tls_strp_copyin);
+
+	return desc.error;
+}
+
+static int tls_strp_read_copy(struct tls_strparser *strp, bool qshort)
+{
+	struct skb_shared_info *shinfo;
+	struct page *page;
+	int need_spc, len;
+
+	/* If the rbuf is small or rcv window has collapsed to 0 we need
+	 * to read the data out. Otherwise the connection will stall.
+	 * Without pressure threshold of INT_MAX will never be ready.
+	 */
+	if (likely(qshort && !tcp_epollin_ready(strp->sk, INT_MAX)))
+		return 0;
+
+	shinfo = skb_shinfo(strp->anchor);
+
+	/* If we don't know the length go max plus page for cipher overhead */
+	need_spc = strp->stm.full_len ?: TLS_MAX_PAYLOAD_SIZE + PAGE_SIZE;
+
+	for (len = need_spc; len > 0; len -= PAGE_SIZE) {
+		page = alloc_page(strp->sk->sk_allocation);
+		if (!page) {
+			tls_strp_flush_anchor_copy(strp);
+			return -ENOMEM;
+		}
+
+		skb_fill_page_desc(strp->anchor, shinfo->nr_frags++,
+				   page, 0, 0);
+	}
+
+	shinfo->frag_list = NULL;
+
+	strp->copy_mode = 1;
+	strp->stm.offset = 0;
+
+	strp->anchor->len = 0;
+	strp->anchor->data_len = 0;
+	strp->anchor->truesize = round_up(need_spc, PAGE_SIZE);
+
+	tls_strp_read_copyin(strp);
+
+	return 0;
+}
+
+static bool tls_strp_check_queue_ok(struct tls_strparser *strp,
+				    unsigned int len)
+{
+	unsigned int remaining = strp->stm.offset + len;
+	struct sk_buff *first, *skb;
+	u32 seq;
+
+	first = skb_shinfo(strp->anchor)->frag_list;
+	skb = first;
+	seq = TCP_SKB_CB(first)->seq;
+
+	/* Make sure there's no duplicate data in the queue,
+	 * and the decrypted status matches.
+	 */
+	while (skb->len < remaining) {
+		seq += skb->len;
+		remaining -= skb->len;
+		skb = skb->next;
+
+		if (TCP_SKB_CB(skb)->seq != seq)
+			return false;
+		if (skb_cmp_decrypted(first, skb))
+			return false;
+	}
+
+	return true;
+}
+
+static void tls_strp_load_anchor_with_queue(struct tls_strparser *strp, int len)
+{
+	struct tcp_sock *tp = tcp_sk(strp->sk);
+	struct sk_buff *first;
+	u32 offset;
+
+	first = tcp_recv_skb(strp->sk, tp->copied_seq, &offset);
+	if (WARN_ON_ONCE(!first))
+		return;
+
+	/* Bestow the state onto the anchor */
+	strp->anchor->len = offset + len;
+	strp->anchor->data_len = offset + len;
+	strp->anchor->truesize = offset + len;
+
+	skb_shinfo(strp->anchor)->frag_list = first;
+
+	skb_copy_header(strp->anchor, first);
+	strp->anchor->destructor = NULL;
+
+	strp->stm.offset = offset;
+}
+
+bool tls_strp_msg_load(struct tls_strparser *strp, bool force_refresh)
+{
+	struct strp_msg *rxm;
+	struct tls_msg *tlm;
+
+	DEBUG_NET_WARN_ON_ONCE(!strp->msg_ready);
+	DEBUG_NET_WARN_ON_ONCE(!strp->stm.full_len);
+
+	if (!strp->copy_mode && force_refresh) {
+		if (unlikely(tcp_inq(strp->sk) < strp->stm.full_len)) {
+			WRITE_ONCE(strp->msg_ready, 0);
+			strp->msg_announced = 0;
+			memset(&strp->stm, 0, sizeof(strp->stm));
+			return false;
+		}
+
+		tls_strp_load_anchor_with_queue(strp, strp->stm.full_len);
+	}
+
+	rxm = strp_msg(strp->anchor);
+	rxm->full_len	= strp->stm.full_len;
+	rxm->offset	= strp->stm.offset;
+	tlm = tls_msg(strp->anchor);
+	tlm->control	= strp->mark;
+
+	return true;
+}
+
+/* Called with lock held on lower socket */
+static int tls_strp_read_sock(struct tls_strparser *strp)
+{
+	int sz, inq;
+
+	inq = tcp_inq(strp->sk);
+	if (inq < 1)
+		return 0;
+
+	if (unlikely(strp->copy_mode))
+		return tls_strp_read_copyin(strp);
+
+	if (inq < strp->stm.full_len)
+		return tls_strp_read_copy(strp, true);
+
+	tls_strp_load_anchor_with_queue(strp, inq);
+	if (!strp->stm.full_len) {
+		if (inq < TLS_HEADER_SIZE)
+			return tls_strp_read_copy(strp, true);
+		if (!tls_strp_check_queue_ok(strp, TLS_HEADER_SIZE))
+			return tls_strp_read_copy(strp, false);
+
+		sz = tls_rx_msg_size(strp, strp->anchor);
+		if (sz < 0)
+			return sz;
+
+		strp->stm.full_len = sz;
+
+		if (!strp->stm.full_len || inq < strp->stm.full_len)
+			return tls_strp_read_copy(strp, true);
+	}
+
+	if (!tls_strp_check_queue_ok(strp, strp->stm.full_len))
+		return tls_strp_read_copy(strp, false);
+
+	WRITE_ONCE(strp->msg_ready, 1);
+
+	return 0;
+}
+
+/* Parse queued data. When @announce is true and parsing produces a
+ * newly-ready record, fire the consumer notification. Callers that
+ * need to notify a waiter about a record parsed by another path
+ * should invoke tls_rx_msg_maybe_announce() directly.
+ */
+void tls_strp_check_rcv(struct tls_strparser *strp, bool announce)
+{
+	if (unlikely(strp->stopped) || strp->msg_ready)
+		return;
+
+	if (tls_strp_read_sock(strp) == -ENOMEM)
+		queue_work(tls_strp_wq, &strp->work);
+	else if (announce && strp->msg_ready)
+		tls_rx_msg_maybe_announce(strp);
+}
+
+/* Lower sock lock held */
+void tls_strp_data_ready(struct tls_strparser *strp)
+{
+	/* This check is needed to synchronize with do_tls_strp_work.
+	 * do_tls_strp_work acquires a process lock (lock_sock) whereas
+	 * the lock held here is bh_lock_sock. The two locks can be
+	 * held by different threads at the same time, but bh_lock_sock
+	 * allows a thread in BH context to safely check if the process
+	 * lock is held. In this case, if the lock is held, queue work.
+	 */
+	if (sock_owned_by_user_nocheck(strp->sk)) {
+		queue_work(tls_strp_wq, &strp->work);
+		return;
+	}
+
+	tls_strp_check_rcv(strp, true);
+}
+
+static void tls_strp_work(struct work_struct *w)
+{
+	struct tls_strparser *strp =
+		container_of(w, struct tls_strparser, work);
+
+	lock_sock(strp->sk);
+	tls_strp_check_rcv(strp, true);
+	release_sock(strp->sk);
+}
+
+/* Release the current record without triggering a check for the
+ * next record. Callers must invoke tls_strp_check_rcv() before
+ * releasing the socket lock, or queued data will stall until the
+ * next tls_strp_data_ready() event.
+ */
+void tls_strp_msg_consume(struct tls_strparser *strp)
+{
+	WARN_ON(!strp->stm.full_len);
+
+	if (likely(!strp->copy_mode))
+		tcp_read_done(strp->sk, strp->stm.full_len);
+	else
+		tls_strp_flush_anchor_copy(strp);
+
+	WRITE_ONCE(strp->msg_ready, 0);
+	strp->msg_announced = 0;
+	memset(&strp->stm, 0, sizeof(strp->stm));
+}
+
+void tls_strp_stop(struct tls_strparser *strp)
+{
+	strp->stopped = 1;
+}
+
+int tls_strp_init(struct tls_strparser *strp, struct sock *sk)
+{
+	memset(strp, 0, sizeof(*strp));
+
+	strp->sk = sk;
+
+	strp->anchor = alloc_skb(0, GFP_KERNEL);
+	if (!strp->anchor)
+		return -ENOMEM;
+
+	INIT_WORK(&strp->work, tls_strp_work);
+
+	return 0;
+}
+
+/* strp must already be stopped so that tls_strp_recv will no longer be called.
+ * Note that tls_strp_done is not called with the lower socket held.
+ */
+void tls_strp_done(struct tls_strparser *strp)
+{
+	WARN_ON(!strp->stopped);
+
+	cancel_work_sync(&strp->work);
+	__tls_strp_done(strp);
+}
+
+/* For setup error paths where the strparser was initialized but never armed. */
+void __tls_strp_done(struct tls_strparser *strp)
+{
+	tls_strp_anchor_free(strp);
+}
+
+int __init tls_strp_dev_init(void)
+{
+	tls_strp_wq = create_workqueue("tls-strp");
+	if (unlikely(!tls_strp_wq))
+		return -ENOMEM;
+
+	return 0;
+}
+
+void tls_strp_dev_exit(void)
+{
+	destroy_workqueue(tls_strp_wq);
+}