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, 143 insertions, 0 deletions

diff --git a/Documentation/driver-api/nvdimm/security.rst b/Documentation/driver-api/nvdimm/security.rst
new file mode 100644
index 000000000..eb3d35e6a
--- /dev/null
+++ b/Documentation/driver-api/nvdimm/security.rst
@@ -0,0 +1,143 @@
+===============
+NVDIMM Security
+===============
+
+1. Introduction
+---------------
+
+With the introduction of Intel Device Specific Methods (DSM) v1.8
+specification [1], security DSMs are introduced. The spec added the following
+security DSMs: "get security state", "set passphrase", "disable passphrase",
+"unlock unit", "freeze lock", "secure erase", and "overwrite". A security_ops
+data structure has been added to struct dimm in order to support the security
+operations and generic APIs are exposed to allow vendor neutral operations.
+
+2. Sysfs Interface
+------------------
+The "security" sysfs attribute is provided in the nvdimm sysfs directory. For
+example:
+/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security
+
+The "show" attribute of that attribute will display the security state for
+that DIMM. The following states are available: disabled, unlocked, locked,
+frozen, and overwrite. If security is not supported, the sysfs attribute
+will not be visible.
+
+The "store" attribute takes several commands when it is being written to
+in order to support some of the security functionalities:
+update <old_keyid> <new_keyid> - enable or update passphrase.
+disable <keyid> - disable enabled security and remove key.
+freeze - freeze changing of security states.
+erase <keyid> - delete existing user encryption key.
+overwrite <keyid> - wipe the entire nvdimm.
+master_update <keyid> <new_keyid> - enable or update master passphrase.
+master_erase <keyid> - delete existing user encryption key.
+
+3. Key Management
+-----------------
+
+The key is associated to the payload by the DIMM id. For example:
+# cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/nfit/id
+8089-a2-1740-00000133
+The DIMM id would be provided along with the key payload (passphrase) to
+the kernel.
+
+The security keys are managed on the basis of a single key per DIMM. The
+key "passphrase" is expected to be 32bytes long. This is similar to the ATA
+security specification [2]. A key is initially acquired via the request_key()
+kernel API call during nvdimm unlock. It is up to the user to make sure that
+all the keys are in the kernel user keyring for unlock.
+
+A nvdimm encrypted-key of format enc32 has the description format of:
+nvdimm:<bus-provider-specific-unique-id>
+
+See file ``Documentation/security/keys/trusted-encrypted.rst`` for creating
+encrypted-keys of enc32 format. TPM usage with a master trusted key is
+preferred for sealing the encrypted-keys.
+
+4. Unlocking
+------------
+When the DIMMs are being enumerated by the kernel, the kernel will attempt to
+retrieve the key from the kernel user keyring. This is the only time
+a locked DIMM can be unlocked. Once unlocked, the DIMM will remain unlocked
+until reboot. Typically an entity (i.e. shell script) will inject all the
+relevant encrypted-keys into the kernel user keyring during the initramfs phase.
+This provides the unlock function access to all the related keys that contain
+the passphrase for the respective nvdimms.  It is also recommended that the
+keys are injected before libnvdimm is loaded by modprobe.
+
+5. Update
+---------
+When doing an update, it is expected that the existing key is removed from
+the kernel user keyring and reinjected as different (old) key. It's irrelevant
+what the key description is for the old key since we are only interested in the
+keyid when doing the update operation. It is also expected that the new key
+is injected with the description format described from earlier in this
+document.  The update command written to the sysfs attribute will be with
+the format:
+update <old keyid> <new keyid>
+
+If there is no old keyid due to a security enabling, then a 0 should be
+passed in.
+
+6. Freeze
+---------
+The freeze operation does not require any keys. The security config can be
+frozen by a user with root privilege.
+
+7. Disable
+----------
+The security disable command format is:
+disable <keyid>
+
+An key with the current passphrase payload that is tied to the nvdimm should be
+in the kernel user keyring.
+
+8. Secure Erase
+---------------
+The command format for doing a secure erase is:
+erase <keyid>
+
+An key with the current passphrase payload that is tied to the nvdimm should be
+in the kernel user keyring.
+
+9. Overwrite
+------------
+The command format for doing an overwrite is:
+overwrite <keyid>
+
+Overwrite can be done without a key if security is not enabled. A key serial
+of 0 can be passed in to indicate no key.
+
+The sysfs attribute "security" can be polled to wait on overwrite completion.
+Overwrite can last tens of minutes or more depending on nvdimm size.
+
+An encrypted-key with the current user passphrase that is tied to the nvdimm
+should be injected and its keyid should be passed in via sysfs.
+
+10. Master Update
+-----------------
+The command format for doing a master update is:
+update <old keyid> <new keyid>
+
+The operating mechanism for master update is identical to update except the
+master passphrase key is passed to the kernel. The master passphrase key
+is just another encrypted-key.
+
+This command is only available when security is disabled.
+
+11. Master Erase
+----------------
+The command format for doing a master erase is:
+master_erase <current keyid>
+
+This command has the same operating mechanism as erase except the master
+passphrase key is passed to the kernel. The master passphrase key is just
+another encrypted-key.
+
+This command is only available when the master security is enabled, indicated
+by the extended security status.
+
+[1]: https://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf
+
+[2]: http://www.t13.org/documents/UploadedDocuments/docs2006/e05179r4-ACS-SecurityClarifications.pdf