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, 90 insertions, 0 deletions

diff --git a/arch/m68k/mac/baboon.c b/arch/m68k/mac/baboon.c
new file mode 100644
index 000000000..5c97a7058
--- /dev/null
+++ b/arch/m68k/mac/baboon.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Baboon Custom IC Management
+ *
+ * The Baboon custom IC controls the IDE, PCMCIA and media bay on the
+ * PowerBook 190. It multiplexes multiple interrupt sources onto the
+ * Nubus slot $C interrupt.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/irq.h>
+
+#include <asm/macintosh.h>
+#include <asm/macints.h>
+#include <asm/mac_baboon.h>
+
+#include "mac.h"
+
+int baboon_present;
+static volatile struct baboon *baboon;
+
+/*
+ * Baboon initialization.
+ */
+
+void __init baboon_init(void)
+{
+	if (macintosh_config->ident != MAC_MODEL_PB190) {
+		baboon = NULL;
+		baboon_present = 0;
+		return;
+	}
+
+	baboon = (struct baboon *) BABOON_BASE;
+	baboon_present = 1;
+
+	pr_debug("Baboon detected at %p\n", baboon);
+}
+
+/*
+ * Baboon interrupt handler.
+ * XXX how do you clear a pending IRQ? is it even necessary?
+ */
+
+static void baboon_irq(struct irq_desc *desc)
+{
+	short events, irq_bit;
+	int irq_num;
+
+	events = baboon->mb_ifr & 0x07;
+	irq_num = IRQ_BABOON_0;
+	irq_bit = 1;
+	do {
+		if (events & irq_bit) {
+			events &= ~irq_bit;
+			generic_handle_irq(irq_num);
+		}
+		++irq_num;
+		irq_bit <<= 1;
+	} while (events);
+}
+
+/*
+ * Register the Baboon interrupt dispatcher on nubus slot $C.
+ */
+
+void __init baboon_register_interrupts(void)
+{
+	irq_set_chained_handler(IRQ_NUBUS_C, baboon_irq);
+}
+
+/*
+ * The means for masking individual Baboon interrupts remains a mystery.
+ * However, since we only use the IDE IRQ, we can just enable/disable all
+ * Baboon interrupts. If/when we handle more than one Baboon IRQ, we must
+ * either figure out how to mask them individually or else implement the
+ * same workaround that's used for NuBus slots (see nubus_disabled and
+ * via_nubus_irq_shutdown).
+ */
+
+void baboon_irq_enable(int irq)
+{
+	mac_irq_enable(irq_get_irq_data(IRQ_NUBUS_C));
+}
+
+void baboon_irq_disable(int irq)
+{
+	mac_irq_disable(irq_get_irq_data(IRQ_NUBUS_C));
+}