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, 200 insertions, 0 deletions

diff --git a/net/bluetooth/ecdh_helper.c b/net/bluetooth/ecdh_helper.c
new file mode 100644
index 000000000..1938e5559
--- /dev/null
+++ b/net/bluetooth/ecdh_helper.c
@@ -0,0 +1,200 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ECDH helper functions - KPP wrappings
+ *
+ * Copyright (C) 2017 Intel Corporation
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS.
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) AND AUTHOR(S) BE LIABLE FOR ANY
+ * CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * ALL LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY PATENTS,
+ * COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS, RELATING TO USE OF THIS
+ * SOFTWARE IS DISCLAIMED.
+ */
+#include "ecdh_helper.h"
+
+#include <linux/scatterlist.h>
+#include <crypto/ecdh.h>
+
+static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
+{
+	int i;
+
+	for (i = 0; i < ndigits; i++)
+		out[i] = __swab64(in[ndigits - 1 - i]);
+}
+
+/* compute_ecdh_secret() - function assumes that the private key was
+ *                         already set.
+ * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
+ * @public_key:   pair's ecc public key.
+ * secret:        memory where the ecdh computed shared secret will be saved.
+ *
+ * Return: zero on success; error code in case of error.
+ */
+int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 public_key[64],
+			u8 secret[32])
+{
+	DECLARE_CRYPTO_WAIT(result);
+	struct kpp_request *req;
+	u8 *tmp;
+	struct scatterlist src, dst;
+	int err;
+
+	tmp = kmalloc(64, GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	req = kpp_request_alloc(tfm, GFP_KERNEL);
+	if (!req) {
+		err = -ENOMEM;
+		goto free_tmp;
+	}
+
+	swap_digits((u64 *)public_key, (u64 *)tmp, 4); /* x */
+	swap_digits((u64 *)&public_key[32], (u64 *)&tmp[32], 4); /* y */
+
+	sg_init_one(&src, tmp, 64);
+	sg_init_one(&dst, secret, 32);
+	kpp_request_set_input(req, &src, 64);
+	kpp_request_set_output(req, &dst, 32);
+	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+				 crypto_req_done, &result);
+	err = crypto_kpp_compute_shared_secret(req);
+	err = crypto_wait_req(err, &result);
+	if (err < 0) {
+		pr_err("alg: ecdh: compute shared secret failed. err %d\n",
+		       err);
+		goto free_all;
+	}
+
+	swap_digits((u64 *)secret, (u64 *)tmp, 4);
+	memcpy(secret, tmp, 32);
+
+free_all:
+	kpp_request_free(req);
+free_tmp:
+	kfree_sensitive(tmp);
+	return err;
+}
+
+/* set_ecdh_privkey() - set or generate ecc private key.
+ *
+ * Function generates an ecc private key in the crypto subsystem when receiving
+ * a NULL private key or sets the received key when not NULL.
+ *
+ * @tfm:           KPP tfm handle allocated with crypto_alloc_kpp().
+ * @private_key:   user's ecc private key. When not NULL, the key is expected
+ *                 in little endian format.
+ *
+ * Return: zero on success; error code in case of error.
+ */
+int set_ecdh_privkey(struct crypto_kpp *tfm, const u8 private_key[32])
+{
+	u8 *buf, *tmp = NULL;
+	unsigned int buf_len;
+	int err;
+	struct ecdh p = {0};
+
+	if (private_key) {
+		tmp = kmalloc(32, GFP_KERNEL);
+		if (!tmp)
+			return -ENOMEM;
+		swap_digits((u64 *)private_key, (u64 *)tmp, 4);
+		p.key = tmp;
+		p.key_size = 32;
+	}
+
+	buf_len = crypto_ecdh_key_len(&p);
+	buf = kmalloc(buf_len, GFP_KERNEL);
+	if (!buf) {
+		err = -ENOMEM;
+		goto free_tmp;
+	}
+
+	err = crypto_ecdh_encode_key(buf, buf_len, &p);
+	if (err)
+		goto free_all;
+
+	err = crypto_kpp_set_secret(tfm, buf, buf_len);
+	/* fall through */
+free_all:
+	kfree_sensitive(buf);
+free_tmp:
+	kfree_sensitive(tmp);
+	return err;
+}
+
+/* generate_ecdh_public_key() - function assumes that the private key was
+ *                              already set.
+ *
+ * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
+ * @public_key:   memory where the computed ecc public key will be saved.
+ *
+ * Return: zero on success; error code in case of error.
+ */
+int generate_ecdh_public_key(struct crypto_kpp *tfm, u8 public_key[64])
+{
+	DECLARE_CRYPTO_WAIT(result);
+	struct kpp_request *req;
+	u8 *tmp;
+	struct scatterlist dst;
+	int err;
+
+	tmp = kmalloc(64, GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	req = kpp_request_alloc(tfm, GFP_KERNEL);
+	if (!req) {
+		err = -ENOMEM;
+		goto free_tmp;
+	}
+
+	sg_init_one(&dst, tmp, 64);
+	kpp_request_set_input(req, NULL, 0);
+	kpp_request_set_output(req, &dst, 64);
+	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+				 crypto_req_done, &result);
+
+	err = crypto_kpp_generate_public_key(req);
+	err = crypto_wait_req(err, &result);
+	if (err < 0)
+		goto free_all;
+
+	/* The public key is handed back in little endian as expected by
+	 * the Security Manager Protocol.
+	 */
+	swap_digits((u64 *)tmp, (u64 *)public_key, 4); /* x */
+	swap_digits((u64 *)&tmp[32], (u64 *)&public_key[32], 4); /* y */
+
+free_all:
+	kpp_request_free(req);
+free_tmp:
+	kfree(tmp);
+	return err;
+}
+
+/* generate_ecdh_keys() - generate ecc key pair.
+ *
+ * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
+ * @public_key:   memory where the computed ecc public key will be saved.
+ *
+ * Return: zero on success; error code in case of error.
+ */
+int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64])
+{
+	int err;
+
+	err = set_ecdh_privkey(tfm, NULL);
+	if (err)
+		return err;
+
+	return generate_ecdh_public_key(tfm, public_key);
+}