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, 175 insertions, 0 deletions

diff --git a/net/sunrpc/auth_tls.c b/net/sunrpc/auth_tls.c
new file mode 100644
index 000000000..87f570fd3
--- /dev/null
+++ b/net/sunrpc/auth_tls.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, 2022 Oracle.  All rights reserved.
+ *
+ * The AUTH_TLS credential is used only to probe a remote peer
+ * for RPC-over-TLS support.
+ */
+
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/sunrpc/clnt.h>
+
+static const char *starttls_token = "STARTTLS";
+static const size_t starttls_len = 8;
+
+static struct rpc_auth tls_auth;
+static struct rpc_cred tls_cred;
+
+static void tls_encode_probe(struct rpc_rqst *rqstp, struct xdr_stream *xdr,
+			     const void *obj)
+{
+}
+
+static int tls_decode_probe(struct rpc_rqst *rqstp, struct xdr_stream *xdr,
+			    void *obj)
+{
+	return 0;
+}
+
+static const struct rpc_procinfo rpcproc_tls_probe = {
+	.p_encode	= tls_encode_probe,
+	.p_decode	= tls_decode_probe,
+};
+
+static void rpc_tls_probe_call_prepare(struct rpc_task *task, void *data)
+{
+	task->tk_flags &= ~RPC_TASK_NO_RETRANS_TIMEOUT;
+	rpc_call_start(task);
+}
+
+static void rpc_tls_probe_call_done(struct rpc_task *task, void *data)
+{
+}
+
+static const struct rpc_call_ops rpc_tls_probe_ops = {
+	.rpc_call_prepare	= rpc_tls_probe_call_prepare,
+	.rpc_call_done		= rpc_tls_probe_call_done,
+};
+
+static int tls_probe(struct rpc_clnt *clnt)
+{
+	struct rpc_message msg = {
+		.rpc_proc	= &rpcproc_tls_probe,
+	};
+	struct rpc_task_setup task_setup_data = {
+		.rpc_client	= clnt,
+		.rpc_message	= &msg,
+		.rpc_op_cred	= &tls_cred,
+		.callback_ops	= &rpc_tls_probe_ops,
+		.flags		= RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
+	};
+	struct rpc_task	*task;
+	int status;
+
+	task = rpc_run_task(&task_setup_data);
+	if (IS_ERR(task))
+		return PTR_ERR(task);
+	status = task->tk_status;
+	rpc_put_task(task);
+	return status;
+}
+
+static struct rpc_auth *tls_create(const struct rpc_auth_create_args *args,
+				   struct rpc_clnt *clnt)
+{
+	refcount_inc(&tls_auth.au_count);
+	return &tls_auth;
+}
+
+static void tls_destroy(struct rpc_auth *auth)
+{
+}
+
+static struct rpc_cred *tls_lookup_cred(struct rpc_auth *auth,
+					struct auth_cred *acred, int flags)
+{
+	return get_rpccred(&tls_cred);
+}
+
+static void tls_destroy_cred(struct rpc_cred *cred)
+{
+}
+
+static int tls_match(struct auth_cred *acred, struct rpc_cred *cred, int taskflags)
+{
+	return 1;
+}
+
+static int tls_marshal(struct rpc_task *task, struct xdr_stream *xdr)
+{
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, 4 * XDR_UNIT);
+	if (!p)
+		return -EMSGSIZE;
+	/* Credential */
+	*p++ = rpc_auth_tls;
+	*p++ = xdr_zero;
+	/* Verifier */
+	*p++ = rpc_auth_null;
+	*p   = xdr_zero;
+	return 0;
+}
+
+static int tls_refresh(struct rpc_task *task)
+{
+	set_bit(RPCAUTH_CRED_UPTODATE, &task->tk_rqstp->rq_cred->cr_flags);
+	return 0;
+}
+
+static int tls_validate(struct rpc_task *task, struct xdr_stream *xdr)
+{
+	__be32 *p;
+	void *str;
+
+	p = xdr_inline_decode(xdr, XDR_UNIT);
+	if (!p)
+		return -EIO;
+	if (*p != rpc_auth_null)
+		return -EIO;
+	if (xdr_stream_decode_opaque_inline(xdr, &str, starttls_len) != starttls_len)
+		return -EPROTONOSUPPORT;
+	if (memcmp(str, starttls_token, starttls_len))
+		return -EPROTONOSUPPORT;
+	return 0;
+}
+
+const struct rpc_authops authtls_ops = {
+	.owner		= THIS_MODULE,
+	.au_flavor	= RPC_AUTH_TLS,
+	.au_name	= "NULL",
+	.create		= tls_create,
+	.destroy	= tls_destroy,
+	.lookup_cred	= tls_lookup_cred,
+	.ping		= tls_probe,
+};
+
+static struct rpc_auth tls_auth = {
+	.au_cslack	= NUL_CALLSLACK,
+	.au_rslack	= NUL_REPLYSLACK,
+	.au_verfsize	= NUL_REPLYSLACK,
+	.au_ralign	= NUL_REPLYSLACK,
+	.au_ops		= &authtls_ops,
+	.au_flavor	= RPC_AUTH_TLS,
+	.au_count	= REFCOUNT_INIT(1),
+};
+
+static const struct rpc_credops tls_credops = {
+	.cr_name	= "AUTH_TLS",
+	.crdestroy	= tls_destroy_cred,
+	.crmatch	= tls_match,
+	.crmarshal	= tls_marshal,
+	.crwrap_req	= rpcauth_wrap_req_encode,
+	.crrefresh	= tls_refresh,
+	.crvalidate	= tls_validate,
+	.crunwrap_resp	= rpcauth_unwrap_resp_decode,
+};
+
+static struct rpc_cred tls_cred = {
+	.cr_lru		= LIST_HEAD_INIT(tls_cred.cr_lru),
+	.cr_auth	= &tls_auth,
+	.cr_ops		= &tls_credops,
+	.cr_count	= REFCOUNT_INIT(2),
+	.cr_flags	= 1UL << RPCAUTH_CRED_UPTODATE,
+};