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, 40 insertions, 0 deletions

diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
new file mode 100644
index 000000000..cd934e31d
--- /dev/null
+++ b/fs/crypto/Kconfig
@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config FS_ENCRYPTION
+	bool "FS Encryption (Per-file encryption)"
+	select BLK_INLINE_ENCRYPTION if BLOCK
+	select BLK_INLINE_ENCRYPTION_FALLBACK if BLOCK
+	select CRYPTO
+	select CRYPTO_SKCIPHER
+	select CRYPTO_LIB_AES
+	select CRYPTO_LIB_SHA256
+	select CRYPTO_LIB_SHA512
+	select KEYS
+	help
+	  Enable encryption of files and directories.  This
+	  feature is similar to ecryptfs, but it is more memory
+	  efficient since it avoids caching the encrypted and
+	  decrypted pages in the page cache.  Currently Ext4,
+	  F2FS, UBIFS, and CephFS make use of this feature.
+
+# Filesystems supporting encryption must select this if FS_ENCRYPTION.  This
+# allows the algorithms to be built as modules when all the filesystems are,
+# whereas selecting them from FS_ENCRYPTION would force them to be built-in.
+#
+# Note: this option only pulls in the algorithms that filesystem encryption
+# needs "by default".  If userspace will use "non-default" encryption modes such
+# as Adiantum encryption, then those other modes need to be explicitly enabled
+# in the crypto API; see Documentation/filesystems/fscrypt.rst for details.
+#
+# Also note that this option only pulls in the generic implementations of the
+# algorithms, not any per-architecture optimized implementations.  It is
+# strongly recommended to enable optimized implementations too.
+config FS_ENCRYPTION_ALGS
+	tristate
+	select CRYPTO_AES
+	select CRYPTO_CBC
+	select CRYPTO_CTS
+	select CRYPTO_XTS
+
+config FS_ENCRYPTION_INLINE_CRYPT
+	bool
+	default y if FS_ENCRYPTION && BLOCK