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, 354 insertions, 0 deletions

diff --git a/drivers/mtd/devices/slram.c b/drivers/mtd/devices/slram.c
new file mode 100644
index 000000000..aa38ecdff
--- /dev/null
+++ b/drivers/mtd/devices/slram.c
@@ -0,0 +1,354 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*======================================================================
+
+  This driver provides a method to access memory not used by the kernel
+  itself (i.e. if the kernel commandline mem=xxx is used). To actually
+  use slram at least mtdblock or mtdchar is required (for block or
+  character device access).
+
+  Usage:
+
+  if compiled as loadable module:
+    modprobe slram map=<name>,<start>,<end/offset>
+  if statically linked into the kernel use the following kernel cmd.line
+    slram=<name>,<start>,<end/offset>
+
+  <name>: name of the device that will be listed in /proc/mtd
+  <start>: start of the memory region, decimal or hex (0xabcdef)
+  <end/offset>: end of the memory region. It's possible to use +0x1234
+                to specify the offset instead of the absolute address
+
+  NOTE:
+  With slram it's only possible to map a contiguous memory region. Therefore
+  if there's a device mapped somewhere in the region specified slram will
+  fail to load (see kernel log if modprobe fails).
+
+  -
+
+  Jochen Schaeuble <psionic@psionic.de>
+
+======================================================================*/
+
+
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/timer.h>
+#include <linux/major.h>
+#include <linux/fs.h>
+#include <linux/ioctl.h>
+#include <linux/init.h>
+#include <linux/io.h>
+
+#include <linux/mtd/mtd.h>
+
+#define SLRAM_MAX_DEVICES_PARAMS 6		/* 3 parameters / device */
+#define SLRAM_BLK_SZ 0x4000
+
+#define T(fmt, args...) printk(KERN_DEBUG fmt, ## args)
+#define E(fmt, args...) printk(KERN_NOTICE fmt, ## args)
+
+typedef struct slram_priv {
+	u_char *start;
+	u_char *end;
+} slram_priv_t;
+
+typedef struct slram_mtd_list {
+	struct mtd_info *mtdinfo;
+	struct slram_mtd_list *next;
+} slram_mtd_list_t;
+
+#ifdef MODULE
+static char *map[SLRAM_MAX_DEVICES_PARAMS];
+
+module_param_array(map, charp, NULL, 0);
+MODULE_PARM_DESC(map, "List of memory regions to map. \"map=<name>, <start>, <length / end>\"");
+#else
+static char *map;
+#endif
+
+static slram_mtd_list_t *slram_mtdlist = NULL;
+
+static int slram_erase(struct mtd_info *, struct erase_info *);
+static int slram_point(struct mtd_info *, loff_t, size_t, size_t *, void **,
+		resource_size_t *);
+static int slram_unpoint(struct mtd_info *, loff_t, size_t);
+static int slram_read(struct mtd_info *, loff_t, size_t, size_t *, u_char *);
+static int slram_write(struct mtd_info *, loff_t, size_t, size_t *, const u_char *);
+
+static int slram_erase(struct mtd_info *mtd, struct erase_info *instr)
+{
+	slram_priv_t *priv = mtd->priv;
+
+	memset(priv->start + instr->addr, 0xff, instr->len);
+
+	return(0);
+}
+
+static int slram_point(struct mtd_info *mtd, loff_t from, size_t len,
+		size_t *retlen, void **virt, resource_size_t *phys)
+{
+	slram_priv_t *priv = mtd->priv;
+
+	*virt = priv->start + from;
+	*retlen = len;
+	return(0);
+}
+
+static int slram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
+{
+	return 0;
+}
+
+static int slram_read(struct mtd_info *mtd, loff_t from, size_t len,
+		size_t *retlen, u_char *buf)
+{
+	slram_priv_t *priv = mtd->priv;
+
+	memcpy(buf, priv->start + from, len);
+	*retlen = len;
+	return(0);
+}
+
+static int slram_write(struct mtd_info *mtd, loff_t to, size_t len,
+		size_t *retlen, const u_char *buf)
+{
+	slram_priv_t *priv = mtd->priv;
+
+	memcpy(priv->start + to, buf, len);
+	*retlen = len;
+	return(0);
+}
+
+/*====================================================================*/
+
+static int register_device(char *name, unsigned long start, unsigned long length)
+{
+	slram_mtd_list_t **curmtd;
+	slram_mtd_list_t *new_mtd;
+	struct mtd_info *mtdinfo;
+	slram_priv_t *priv;
+	int ret = -ENOMEM;
+
+	curmtd = &slram_mtdlist;
+	while (*curmtd) {
+		curmtd = &(*curmtd)->next;
+	}
+
+	new_mtd = kmalloc_obj(slram_mtd_list_t);
+	if (!new_mtd) {
+		E("slram: Cannot allocate new MTD device.\n");
+		return(-ENOMEM);
+	}
+	new_mtd->next = NULL;
+
+	mtdinfo = kzalloc_obj(struct mtd_info);
+	if (!mtdinfo) {
+		E("slram: Cannot allocate new MTD device.\n");
+		goto err_free_list;
+	}
+	new_mtd->mtdinfo = mtdinfo;
+
+	priv = kzalloc_obj(slram_priv_t);
+	if (!priv) {
+		E("slram: Cannot allocate new MTD device.\n");
+		goto err_free_mtdinfo;
+	}
+	mtdinfo->priv = priv;
+
+	priv->start = memremap(start, length,
+			       MEMREMAP_WB | MEMREMAP_WT | MEMREMAP_WC);
+	if (!priv->start) {
+		E("slram: memremap failed\n");
+		ret = -EIO;
+		goto err_free_priv;
+	}
+	priv->end = priv->start + length;
+
+	mtdinfo->name = name;
+	mtdinfo->size = length;
+	mtdinfo->flags = MTD_CAP_RAM;
+	mtdinfo->_erase = slram_erase;
+	mtdinfo->_point = slram_point;
+	mtdinfo->_unpoint = slram_unpoint;
+	mtdinfo->_read = slram_read;
+	mtdinfo->_write = slram_write;
+	mtdinfo->owner = THIS_MODULE;
+	mtdinfo->type = MTD_RAM;
+	mtdinfo->erasesize = SLRAM_BLK_SZ;
+	mtdinfo->writesize = 1;
+
+	if (mtd_device_register(mtdinfo, NULL, 0)) {
+		E("slram: Failed to register new device\n");
+		ret = -EAGAIN;
+		goto err_unmap;
+	}
+	*curmtd = new_mtd;
+	T("slram: Registered device %s from %luKiB to %luKiB\n", name,
+			(start / 1024), ((start + length) / 1024));
+	T("slram: Mapped from 0x%p to 0x%p\n", priv->start, priv->end);
+	return 0;
+
+err_unmap:
+	memunmap(priv->start);
+err_free_priv:
+	kfree(priv);
+err_free_mtdinfo:
+	kfree(mtdinfo);
+err_free_list:
+	kfree(new_mtd);
+	return ret;
+}
+
+static void unregister_devices(void)
+{
+	slram_mtd_list_t *nextitem;
+
+	while (slram_mtdlist) {
+		nextitem = slram_mtdlist->next;
+		mtd_device_unregister(slram_mtdlist->mtdinfo);
+		memunmap(((slram_priv_t *)slram_mtdlist->mtdinfo->priv)->start);
+		kfree(slram_mtdlist->mtdinfo->priv);
+		kfree(slram_mtdlist->mtdinfo);
+		kfree(slram_mtdlist);
+		slram_mtdlist = nextitem;
+	}
+}
+
+static unsigned long handle_unit(unsigned long value, char *unit)
+{
+	if ((*unit == 'M') || (*unit == 'm')) {
+		return(value * 1024 * 1024);
+	} else if ((*unit == 'K') || (*unit == 'k')) {
+		return(value * 1024);
+	}
+	return(value);
+}
+
+static int parse_cmdline(char *devname, char *szstart, char *szlength)
+{
+	char *buffer;
+	unsigned long devstart;
+	unsigned long devlength;
+
+	if ((!devname) || (!szstart) || (!szlength)) {
+		unregister_devices();
+		return(-EINVAL);
+	}
+
+	devstart = simple_strtoul(szstart, &buffer, 0);
+	devstart = handle_unit(devstart, buffer);
+
+	if (*(szlength) != '+') {
+		devlength = simple_strtoul(szlength, &buffer, 0);
+		devlength = handle_unit(devlength, buffer);
+		if (devlength < devstart)
+			goto err_out;
+
+		devlength -= devstart;
+	} else {
+		devlength = simple_strtoul(szlength + 1, &buffer, 0);
+		devlength = handle_unit(devlength, buffer);
+	}
+	T("slram: devname=%s, devstart=0x%lx, devlength=0x%lx\n",
+			devname, devstart, devlength);
+	if (devlength % SLRAM_BLK_SZ != 0)
+		goto err_out;
+
+	if ((devstart = register_device(devname, devstart, devlength))){
+		unregister_devices();
+		return((int)devstart);
+	}
+	return(0);
+
+err_out:
+	E("slram: Illegal length parameter.\n");
+	return(-EINVAL);
+}
+
+#ifndef MODULE
+
+static int __init mtd_slram_setup(char *str)
+{
+	map = str;
+	return(1);
+}
+
+__setup("slram=", mtd_slram_setup);
+
+#endif
+
+static int __init init_slram(void)
+{
+	char *devname;
+
+#ifndef MODULE
+	char *devstart;
+	char *devlength;
+
+	if (!map) {
+		E("slram: not enough parameters.\n");
+		return(-EINVAL);
+	}
+	while (map) {
+		devname = devstart = devlength = NULL;
+
+		if (!(devname = strsep(&map, ","))) {
+			E("slram: No devicename specified.\n");
+			break;
+		}
+		T("slram: devname = %s\n", devname);
+		if ((!map) || (!(devstart = strsep(&map, ",")))) {
+			E("slram: No devicestart specified.\n");
+			break;
+		}
+		T("slram: devstart = %s\n", devstart);
+		if ((!map) || (!(devlength = strsep(&map, ",")))) {
+			E("slram: No devicelength / -end specified.\n");
+			break;
+		}
+		T("slram: devlength = %s\n", devlength);
+		if (parse_cmdline(devname, devstart, devlength) != 0) {
+			return(-EINVAL);
+		}
+	}
+#else
+	int count;
+	int i;
+
+	for (count = 0; count < SLRAM_MAX_DEVICES_PARAMS && map[count];
+			count++) {
+	}
+
+	if ((count % 3 != 0) || (count == 0)) {
+		E("slram: not enough parameters.\n");
+		return(-EINVAL);
+	}
+	for (i = 0; i < (count / 3); i++) {
+		devname = map[i * 3];
+
+		if (parse_cmdline(devname, map[i * 3 + 1], map[i * 3 + 2])!=0) {
+			return(-EINVAL);
+		}
+
+	}
+#endif /* !MODULE */
+
+	return(0);
+}
+
+static void __exit cleanup_slram(void)
+{
+	unregister_devices();
+}
+
+module_init(init_slram);
+module_exit(cleanup_slram);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jochen Schaeuble <psionic@psionic.de>");
+MODULE_DESCRIPTION("MTD driver for uncached system RAM");