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, 244 insertions, 0 deletions

diff --git a/drivers/media/firewire/firedtv-dvb.c b/drivers/media/firewire/firedtv-dvb.c
new file mode 100644
index 000000000..3b7e2f1ec
--- /dev/null
+++ b/drivers/media/firewire/firedtv-dvb.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * FireDTV driver (formerly known as FireSAT)
+ *
+ * Copyright (C) 2004 Andreas Monitzer <andy@monitzer.com>
+ * Copyright (C) 2008 Henrik Kurelid <henrik@kurelid.se>
+ */
+
+#include <linux/bitops.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#include <media/dmxdev.h>
+#include <media/dvb_demux.h>
+#include <media/dvbdev.h>
+#include <media/dvb_frontend.h>
+
+#include "firedtv.h"
+
+static int alloc_channel(struct firedtv *fdtv)
+{
+	int i;
+
+	for (i = 0; i < 16; i++)
+		if (!__test_and_set_bit(i, &fdtv->channel_active))
+			break;
+	return i;
+}
+
+static void collect_channels(struct firedtv *fdtv, int *pidc, u16 pid[])
+{
+	int i, n;
+
+	for (i = 0, n = 0; i < 16; i++)
+		if (test_bit(i, &fdtv->channel_active))
+			pid[n++] = fdtv->channel_pid[i];
+	*pidc = n;
+}
+
+static inline void dealloc_channel(struct firedtv *fdtv, int i)
+{
+	__clear_bit(i, &fdtv->channel_active);
+}
+
+int fdtv_start_feed(struct dvb_demux_feed *dvbdmxfeed)
+{
+	struct firedtv *fdtv = dvbdmxfeed->demux->priv;
+	int pidc, c, ret;
+	u16 pids[16];
+
+	switch (dvbdmxfeed->type) {
+	case DMX_TYPE_TS:
+	case DMX_TYPE_SEC:
+		break;
+	default:
+		dev_err(fdtv->device, "can't start dmx feed: invalid type %u\n",
+			dvbdmxfeed->type);
+		return -EINVAL;
+	}
+
+	if (mutex_lock_interruptible(&fdtv->demux_mutex))
+		return -EINTR;
+
+	if (dvbdmxfeed->type == DMX_TYPE_TS) {
+		switch (dvbdmxfeed->pes_type) {
+		case DMX_PES_VIDEO:
+		case DMX_PES_AUDIO:
+		case DMX_PES_TELETEXT:
+		case DMX_PES_PCR:
+		case DMX_PES_OTHER:
+			c = alloc_channel(fdtv);
+			break;
+		default:
+			dev_err(fdtv->device,
+				"can't start dmx feed: invalid pes type %u\n",
+				dvbdmxfeed->pes_type);
+			ret = -EINVAL;
+			goto out;
+		}
+	} else {
+		c = alloc_channel(fdtv);
+	}
+
+	if (c > 15) {
+		dev_err(fdtv->device, "can't start dmx feed: busy\n");
+		ret = -EBUSY;
+		goto out;
+	}
+
+	dvbdmxfeed->priv = (typeof(dvbdmxfeed->priv))(unsigned long)c;
+	fdtv->channel_pid[c] = dvbdmxfeed->pid;
+	collect_channels(fdtv, &pidc, pids);
+
+	if (dvbdmxfeed->pid == 8192) {
+		ret = avc_tuner_get_ts(fdtv);
+		if (ret) {
+			dealloc_channel(fdtv, c);
+			dev_err(fdtv->device, "can't get TS\n");
+			goto out;
+		}
+	} else {
+		ret = avc_tuner_set_pids(fdtv, pidc, pids);
+		if (ret) {
+			dealloc_channel(fdtv, c);
+			dev_err(fdtv->device, "can't set PIDs\n");
+			goto out;
+		}
+	}
+out:
+	mutex_unlock(&fdtv->demux_mutex);
+
+	return ret;
+}
+
+int fdtv_stop_feed(struct dvb_demux_feed *dvbdmxfeed)
+{
+	struct dvb_demux *demux = dvbdmxfeed->demux;
+	struct firedtv *fdtv = demux->priv;
+	int pidc, c, ret;
+	u16 pids[16];
+
+	if (dvbdmxfeed->type == DMX_TYPE_TS &&
+	    !((dvbdmxfeed->ts_type & TS_PACKET) &&
+	      (demux->dmx.frontend->source != DMX_MEMORY_FE))) {
+
+		if (dvbdmxfeed->ts_type & TS_DECODER) {
+			if (dvbdmxfeed->pes_type >= DMX_PES_OTHER ||
+			    !demux->pesfilter[dvbdmxfeed->pes_type])
+				return -EINVAL;
+
+			demux->pids[dvbdmxfeed->pes_type] |= 0x8000;
+			demux->pesfilter[dvbdmxfeed->pes_type] = NULL;
+		}
+
+		if (!(dvbdmxfeed->ts_type & TS_DECODER &&
+		      dvbdmxfeed->pes_type < DMX_PES_OTHER))
+			return 0;
+	}
+
+	if (mutex_lock_interruptible(&fdtv->demux_mutex))
+		return -EINTR;
+
+	c = (unsigned long)dvbdmxfeed->priv;
+	dealloc_channel(fdtv, c);
+	collect_channels(fdtv, &pidc, pids);
+
+	ret = avc_tuner_set_pids(fdtv, pidc, pids);
+
+	mutex_unlock(&fdtv->demux_mutex);
+
+	return ret;
+}
+
+DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);
+
+int fdtv_dvb_register(struct firedtv *fdtv, const char *name)
+{
+	int err;
+
+	err = dvb_register_adapter(&fdtv->adapter, name,
+				   THIS_MODULE, fdtv->device, adapter_nr);
+	if (err < 0)
+		goto fail_log;
+
+	/*DMX_TS_FILTERING | DMX_SECTION_FILTERING*/
+	fdtv->demux.dmx.capabilities = 0;
+
+	fdtv->demux.priv	= fdtv;
+	fdtv->demux.filternum	= 16;
+	fdtv->demux.feednum	= 16;
+	fdtv->demux.start_feed	= fdtv_start_feed;
+	fdtv->demux.stop_feed	= fdtv_stop_feed;
+	fdtv->demux.write_to_decoder = NULL;
+
+	err = dvb_dmx_init(&fdtv->demux);
+	if (err)
+		goto fail_unreg_adapter;
+
+	fdtv->dmxdev.filternum    = 16;
+	fdtv->dmxdev.demux        = &fdtv->demux.dmx;
+	fdtv->dmxdev.capabilities = 0;
+
+	err = dvb_dmxdev_init(&fdtv->dmxdev, &fdtv->adapter);
+	if (err)
+		goto fail_dmx_release;
+
+	fdtv->frontend.source = DMX_FRONTEND_0;
+
+	err = fdtv->demux.dmx.add_frontend(&fdtv->demux.dmx, &fdtv->frontend);
+	if (err)
+		goto fail_dmxdev_release;
+
+	err = fdtv->demux.dmx.connect_frontend(&fdtv->demux.dmx,
+					       &fdtv->frontend);
+	if (err)
+		goto fail_rem_frontend;
+
+	err = dvb_net_init(&fdtv->adapter, &fdtv->dvbnet, &fdtv->demux.dmx);
+	if (err)
+		goto fail_disconnect_frontend;
+
+	fdtv_frontend_init(fdtv, name);
+	err = dvb_register_frontend(&fdtv->adapter, &fdtv->fe);
+	if (err)
+		goto fail_net_release;
+
+	err = fdtv_ca_register(fdtv);
+	if (err)
+		dev_info(fdtv->device,
+			 "Conditional Access Module not enabled\n");
+	return 0;
+
+fail_net_release:
+	dvb_net_release(&fdtv->dvbnet);
+fail_disconnect_frontend:
+	fdtv->demux.dmx.close(&fdtv->demux.dmx);
+fail_rem_frontend:
+	fdtv->demux.dmx.remove_frontend(&fdtv->demux.dmx, &fdtv->frontend);
+fail_dmxdev_release:
+	dvb_dmxdev_release(&fdtv->dmxdev);
+fail_dmx_release:
+	dvb_dmx_release(&fdtv->demux);
+fail_unreg_adapter:
+	dvb_unregister_adapter(&fdtv->adapter);
+fail_log:
+	dev_err(fdtv->device, "DVB initialization failed\n");
+	return err;
+}
+
+void fdtv_dvb_unregister(struct firedtv *fdtv)
+{
+	fdtv_ca_release(fdtv);
+	dvb_unregister_frontend(&fdtv->fe);
+	dvb_net_release(&fdtv->dvbnet);
+	fdtv->demux.dmx.close(&fdtv->demux.dmx);
+	fdtv->demux.dmx.remove_frontend(&fdtv->demux.dmx, &fdtv->frontend);
+	dvb_dmxdev_release(&fdtv->dmxdev);
+	dvb_dmx_release(&fdtv->demux);
+	dvb_unregister_adapter(&fdtv->adapter);
+}