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, 144 insertions, 0 deletions

diff --git a/Documentation/filesystems/ext4/blocks.rst b/Documentation/filesystems/ext4/blocks.rst
new file mode 100644
index 000000000..b0f80ea87
--- /dev/null
+++ b/Documentation/filesystems/ext4/blocks.rst
@@ -0,0 +1,144 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Blocks
+------
+
+ext4 allocates storage space in units of “blocks”. A block is a group of
+sectors between 1KiB and 64KiB, and the number of sectors must be an
+integral power of 2. Blocks are in turn grouped into larger units called
+block groups. Block size is specified at mkfs time and typically is
+4KiB. You may experience mounting problems if block size is greater than
+page size (i.e. 64KiB blocks on a i386 which only has 4KiB memory
+pages). By default a filesystem can contain 2^32 blocks; if the '64bit'
+feature is enabled, then a filesystem can have 2^64 blocks. The location
+of structures is stored in terms of the block number the structure lives
+in and not the absolute offset on disk.
+
+For 32-bit filesystems, limits are as follows:
+
+.. list-table::
+   :widths: 1 1 1 1 1
+   :header-rows: 1
+
+   * - Item
+     - 1KiB
+     - 2KiB
+     - 4KiB
+     - 64KiB
+   * - Blocks
+     - 2^32
+     - 2^32
+     - 2^32
+     - 2^32
+   * - Inodes
+     - 2^32
+     - 2^32
+     - 2^32
+     - 2^32
+   * - File System Size
+     - 4TiB
+     - 8TiB
+     - 16TiB
+     - 256TiB
+   * - Blocks Per Block Group
+     - 8,192
+     - 16,384
+     - 32,768
+     - 524,288
+   * - Inodes Per Block Group
+     - 8,192
+     - 16,384
+     - 32,768
+     - 524,288
+   * - Block Group Size
+     - 8MiB
+     - 32MiB
+     - 128MiB
+     - 32GiB
+   * - Blocks Per File, Extents
+     - 2^32
+     - 2^32
+     - 2^32
+     - 2^32
+   * - Blocks Per File, Block Maps
+     - 16,843,020
+     - 134,480,396
+     - 1,074,791,436
+     - 4,398,314,962,956 (really 2^32 due to field size limitations)
+   * - File Size, Extents
+     - 4TiB
+     - 8TiB
+     - 16TiB
+     - 256TiB
+   * - File Size, Block Maps
+     - 16GiB
+     - 256GiB
+     - 4TiB
+     - 256TiB
+
+For 64-bit filesystems, limits are as follows:
+
+.. list-table::
+   :widths: 1 1 1 1 1
+   :header-rows: 1
+
+   * - Item
+     - 1KiB
+     - 2KiB
+     - 4KiB
+     - 64KiB
+   * - Blocks
+     - 2^64
+     - 2^64
+     - 2^64
+     - 2^64
+   * - Inodes
+     - 2^32
+     - 2^32
+     - 2^32
+     - 2^32
+   * - File System Size
+     - 16ZiB
+     - 32ZiB
+     - 64ZiB
+     - 1YiB
+   * - Blocks Per Block Group
+     - 8,192
+     - 16,384
+     - 32,768
+     - 524,288
+   * - Inodes Per Block Group
+     - 8,192
+     - 16,384
+     - 32,768
+     - 524,288
+   * - Block Group Size
+     - 8MiB
+     - 32MiB
+     - 128MiB
+     - 32GiB
+   * - Blocks Per File, Extents
+     - 2^32
+     - 2^32
+     - 2^32
+     - 2^32
+   * - Blocks Per File, Block Maps
+     - 16,843,020
+     - 134,480,396
+     - 1,074,791,436
+     - 4,398,314,962,956 (really 2^32 due to field size limitations)
+   * - File Size, Extents
+     - 4TiB
+     - 8TiB
+     - 16TiB
+     - 256TiB
+   * - File Size, Block Maps
+     - 16GiB
+     - 256GiB
+     - 4TiB
+     - 256TiB
+
+Note: Files not using extents (i.e. files using block maps) must be
+placed within the first 2^32 blocks of a filesystem. Files with extents
+must be placed within the first 2^48 blocks of a filesystem. It's not
+clear what happens with larger filesystems.