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, 259 insertions, 0 deletions

diff --git a/drivers/memory/dfl-emif.c b/drivers/memory/dfl-emif.c
new file mode 100644
index 000000000..da06cd30a
--- /dev/null
+++ b/drivers/memory/dfl-emif.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DFL device driver for EMIF private feature
+ *
+ * Copyright (C) 2020 Intel Corporation, Inc.
+ *
+ */
+#include <linux/bitfield.h>
+#include <linux/dfl.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+
+#define FME_FEATURE_ID_EMIF		0x9
+
+#define EMIF_STAT			0x8
+#define EMIF_STAT_INIT_DONE_SFT		0
+#define EMIF_STAT_CALC_FAIL_SFT		8
+#define EMIF_STAT_CLEAR_BUSY_SFT	16
+#define EMIF_CTRL			0x10
+#define EMIF_CTRL_CLEAR_EN_SFT		0
+#define EMIF_CTRL_CLEAR_EN_MSK		GENMASK_ULL(7, 0)
+
+#define EMIF_POLL_INVL			10000 /* us */
+#define EMIF_POLL_TIMEOUT		5000000 /* us */
+
+/*
+ * The Capability Register replaces the Control Register (at the same
+ * offset) for EMIF feature revisions > 0. The bitmask that indicates
+ * the presence of memory channels exists in both the Capability Register
+ * and Control Register definitions. These can be thought of as a C union.
+ * The Capability Register definitions are used to check for the existence
+ * of a memory channel, and the Control Register definitions are used for
+ * managing the memory-clear functionality in revision 0.
+ */
+#define EMIF_CAPABILITY_BASE		0x10
+#define EMIF_CAPABILITY_CHN_MSK_V0	GENMASK_ULL(3, 0)
+#define EMIF_CAPABILITY_CHN_MSK		GENMASK_ULL(7, 0)
+
+struct dfl_emif {
+	struct device *dev;
+	void __iomem *base;
+	spinlock_t lock;	/* Serialises access to EMIF_CTRL reg */
+};
+
+struct emif_attr {
+	struct device_attribute attr;
+	u32 shift;
+	u32 index;
+};
+
+#define to_emif_attr(dev_attr) \
+	container_of(dev_attr, struct emif_attr, attr)
+
+static ssize_t emif_state_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct emif_attr *eattr = to_emif_attr(attr);
+	struct dfl_emif *de = dev_get_drvdata(dev);
+	u64 val;
+
+	val = readq(de->base + EMIF_STAT);
+
+	return sysfs_emit(buf, "%u\n",
+			  !!(val & BIT_ULL(eattr->shift + eattr->index)));
+}
+
+static ssize_t emif_clear_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct emif_attr *eattr = to_emif_attr(attr);
+	struct dfl_emif *de = dev_get_drvdata(dev);
+	u64 clear_busy_msk, clear_en_msk, val;
+	void __iomem *base = de->base;
+
+	if (!sysfs_streq(buf, "1"))
+		return -EINVAL;
+
+	clear_busy_msk = BIT_ULL(EMIF_STAT_CLEAR_BUSY_SFT + eattr->index);
+	clear_en_msk = BIT_ULL(EMIF_CTRL_CLEAR_EN_SFT + eattr->index);
+
+	spin_lock(&de->lock);
+	/* The CLEAR_EN field is WO, but other fields are RW */
+	val = readq(base + EMIF_CTRL);
+	val &= ~EMIF_CTRL_CLEAR_EN_MSK;
+	val |= clear_en_msk;
+	writeq(val, base + EMIF_CTRL);
+	spin_unlock(&de->lock);
+
+	if (readq_poll_timeout(base + EMIF_STAT, val,
+			       !(val & clear_busy_msk),
+			       EMIF_POLL_INVL, EMIF_POLL_TIMEOUT)) {
+		dev_err(de->dev, "timeout, fail to clear\n");
+		return -ETIMEDOUT;
+	}
+
+	return count;
+}
+
+#define emif_state_attr(_name, _shift, _index)				\
+	static struct emif_attr emif_attr_##inf##_index##_##_name =	\
+		{ .attr = __ATTR(inf##_index##_##_name, 0444,		\
+				 emif_state_show, NULL),		\
+		  .shift = (_shift), .index = (_index) }
+
+#define emif_clear_attr(_index)						\
+	static struct emif_attr emif_attr_##inf##_index##_clear =	\
+		{ .attr = __ATTR(inf##_index##_clear, 0200,		\
+				 NULL, emif_clear_store),		\
+		  .index = (_index) }
+
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 0);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 1);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 2);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 3);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 4);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 5);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 6);
+emif_state_attr(init_done, EMIF_STAT_INIT_DONE_SFT, 7);
+
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 0);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 1);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 2);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 3);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 4);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 5);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 6);
+emif_state_attr(cal_fail, EMIF_STAT_CALC_FAIL_SFT, 7);
+
+
+emif_clear_attr(0);
+emif_clear_attr(1);
+emif_clear_attr(2);
+emif_clear_attr(3);
+emif_clear_attr(4);
+emif_clear_attr(5);
+emif_clear_attr(6);
+emif_clear_attr(7);
+
+
+static struct attribute *dfl_emif_attrs[] = {
+	&emif_attr_inf0_init_done.attr.attr,
+	&emif_attr_inf0_cal_fail.attr.attr,
+	&emif_attr_inf0_clear.attr.attr,
+
+	&emif_attr_inf1_init_done.attr.attr,
+	&emif_attr_inf1_cal_fail.attr.attr,
+	&emif_attr_inf1_clear.attr.attr,
+
+	&emif_attr_inf2_init_done.attr.attr,
+	&emif_attr_inf2_cal_fail.attr.attr,
+	&emif_attr_inf2_clear.attr.attr,
+
+	&emif_attr_inf3_init_done.attr.attr,
+	&emif_attr_inf3_cal_fail.attr.attr,
+	&emif_attr_inf3_clear.attr.attr,
+
+	&emif_attr_inf4_init_done.attr.attr,
+	&emif_attr_inf4_cal_fail.attr.attr,
+	&emif_attr_inf4_clear.attr.attr,
+
+	&emif_attr_inf5_init_done.attr.attr,
+	&emif_attr_inf5_cal_fail.attr.attr,
+	&emif_attr_inf5_clear.attr.attr,
+
+	&emif_attr_inf6_init_done.attr.attr,
+	&emif_attr_inf6_cal_fail.attr.attr,
+	&emif_attr_inf6_clear.attr.attr,
+
+	&emif_attr_inf7_init_done.attr.attr,
+	&emif_attr_inf7_cal_fail.attr.attr,
+	&emif_attr_inf7_clear.attr.attr,
+
+	NULL,
+};
+
+static umode_t dfl_emif_visible(struct kobject *kobj,
+				struct attribute *attr, int n)
+{
+	struct dfl_emif *de = dev_get_drvdata(kobj_to_dev(kobj));
+	struct emif_attr *eattr = container_of(attr, struct emif_attr,
+					       attr.attr);
+	struct dfl_device *ddev = to_dfl_dev(de->dev);
+	u64 val;
+
+	/*
+	 * This device supports up to 8 memory interfaces, but not all
+	 * interfaces are used on different platforms. The read out value of
+	 * CAPABILITY_CHN_MSK field (which is a bitmap) indicates which
+	 * interfaces are available.
+	 */
+	if (ddev->revision > 0 && strstr(attr->name, "_clear"))
+		return 0;
+
+	if (ddev->revision == 0)
+		val = FIELD_GET(EMIF_CAPABILITY_CHN_MSK_V0,
+				readq(de->base + EMIF_CAPABILITY_BASE));
+	else
+		val = FIELD_GET(EMIF_CAPABILITY_CHN_MSK,
+				readq(de->base + EMIF_CAPABILITY_BASE));
+
+	return (val & BIT_ULL(eattr->index)) ? attr->mode : 0;
+}
+
+static const struct attribute_group dfl_emif_group = {
+	.is_visible = dfl_emif_visible,
+	.attrs = dfl_emif_attrs,
+};
+
+static const struct attribute_group *dfl_emif_groups[] = {
+	&dfl_emif_group,
+	NULL,
+};
+
+static int dfl_emif_probe(struct dfl_device *ddev)
+{
+	struct device *dev = &ddev->dev;
+	struct dfl_emif *de;
+
+	de = devm_kzalloc(dev, sizeof(*de), GFP_KERNEL);
+	if (!de)
+		return -ENOMEM;
+
+	de->base = devm_ioremap_resource(dev, &ddev->mmio_res);
+	if (IS_ERR(de->base))
+		return PTR_ERR(de->base);
+
+	de->dev = dev;
+	spin_lock_init(&de->lock);
+	dev_set_drvdata(dev, de);
+
+	return 0;
+}
+
+static const struct dfl_device_id dfl_emif_ids[] = {
+	{ FME_ID, FME_FEATURE_ID_EMIF },
+	{ }
+};
+MODULE_DEVICE_TABLE(dfl, dfl_emif_ids);
+
+static struct dfl_driver dfl_emif_driver = {
+	.drv	= {
+		.name       = "dfl-emif",
+		.dev_groups = dfl_emif_groups,
+	},
+	.id_table = dfl_emif_ids,
+	.probe   = dfl_emif_probe,
+};
+module_dfl_driver(dfl_emif_driver);
+
+MODULE_DESCRIPTION("DFL EMIF driver");
+MODULE_AUTHOR("Intel Corporation");
+MODULE_LICENSE("GPL v2");