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, 49 insertions, 0 deletions

diff --git a/Documentation/crypto/libcrypto-unauth-encryption.rst b/Documentation/crypto/libcrypto-unauth-encryption.rst
new file mode 100644
index 000000000..b4639b892
--- /dev/null
+++ b/Documentation/crypto/libcrypto-unauth-encryption.rst
@@ -0,0 +1,49 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Unauthenticated encryption
+==========================
+
+These APIs provide support for unauthenticated encryption and decryption,
+including bare stream ciphers and other length-preserving algorithms such as
+block ciphers in XTS mode.  The legitimate use cases for these algorithms are:
+
+- Support for legacy protocols that really should have chosen an authenticated
+  mode (or even another primitive entirely) but didn't.
+
+- Internal components of authenticated modes.  For example, AES-CTR is used by
+  AES-GCM and AES-CCM internally.
+
+- Storage encryption that cannot accommodate ciphertext expansion.  Usually
+  AES-XTS is used for this.
+
+- Stream ciphers for key derivation and random number generation.
+
+Besides the above, these shouldn't be used.
+
+AES-CBC and AES-CBC-CTS
+-----------------------
+
+This API provides support for AES in the CBC and CBC-CTS modes of operation.
+
+.. kernel-doc:: include/crypto/aes-cbc.h
+
+AES-CTR and AES-XCTR
+--------------------
+
+This API provides support for AES in the CTR and XCTR modes of operation.
+
+.. kernel-doc:: include/crypto/aes-ctr.h
+
+AES-ECB
+-------
+
+This API provides support for AES in the ECB mode of operation.
+
+.. kernel-doc:: include/crypto/aes-ecb.h
+
+AES-XTS
+-------
+
+This API provides support for AES in the XTS mode of operation.
+
+.. kernel-doc:: include/crypto/aes-xts.h