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, 85 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-edac-scrub b/Documentation/ABI/testing/sysfs-edac-scrub
new file mode 100644
index 000000000..ab6014743
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-edac-scrub
@@ -0,0 +1,85 @@
+What:		/sys/bus/edac/devices/<dev-name>/scrubX
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		The sysfs EDAC bus devices /<dev-name>/scrubX subdirectory
+		belongs to an instance of memory scrub control feature,
+		where <dev-name> directory corresponds to a device/memory
+		region registered with the EDAC device driver for the
+		scrub control feature.
+
+		The sysfs scrub attr nodes are only present if the parent
+		driver has implemented the corresponding attr callback
+		function and provided the necessary operations to the EDAC
+		device driver during registration.
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/addr
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) The base address of the memory region to be scrubbed
+		for on-demand scrubbing. Setting address starts scrubbing.
+		The size must be set before that.
+
+		The readback addr value is non-zero if the requested
+		on-demand scrubbing is in progress, zero otherwise.
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/size
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) The size of the memory region to be scrubbed
+		(on-demand scrubbing).
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/enable_background
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) Start/Stop background (patrol) scrubbing if supported.
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/min_cycle_duration
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RO) Supported minimum scrub cycle duration in seconds
+		by the memory scrubber.
+
+		Device-based scrub: returns the minimum scrub cycle
+		supported by the memory device.
+
+		Region-based scrub: returns the max of minimum scrub cycles
+		supported by individual memory devices that back the region.
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/max_cycle_duration
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RO) Supported maximum scrub cycle duration in seconds
+		by the memory scrubber.
+
+		Device-based scrub: returns the maximum scrub cycle supported
+		by the memory device.
+
+		Region-based scrub: returns the min of maximum scrub cycles
+		supported by individual memory devices that back the region.
+
+		If the memory device does not provide maximum scrub cycle
+		information, return the maximum supported value of the scrub
+		cycle field.
+
+What:		/sys/bus/edac/devices/<dev-name>/scrubX/current_cycle_duration
+Date:		March 2025
+KernelVersion:	6.15
+Contact:	linux-edac@vger.kernel.org
+Description:
+		(RW) The current scrub cycle duration in seconds and must be
+		within the supported range by the memory scrubber.
+
+		Scrub has an overhead when running and that may want to be
+		reduced by taking longer to do it.