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, 437 insertions, 0 deletions

diff --git a/drivers/mtd/tests/subpagetest.c b/drivers/mtd/tests/subpagetest.c
new file mode 100644
index 000000000..f34bbf033
--- /dev/null
+++ b/drivers/mtd/tests/subpagetest.c
@@ -0,0 +1,437 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2006-2007 Nokia Corporation
+ *
+ * Test sub-page read and write on MTD device.
+ * Author: Adrian Hunter <ext-adrian.hunter@nokia.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/err.h>
+#include <linux/mtd/mtd.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/prandom.h>
+
+#include "mtd_test.h"
+
+static int dev = -EINVAL;
+module_param(dev, int, S_IRUGO);
+MODULE_PARM_DESC(dev, "MTD device number to use");
+
+static struct mtd_info *mtd;
+static unsigned char *writebuf;
+static unsigned char *readbuf;
+static unsigned char *bbt;
+
+static int subpgsize;
+static int bufsize;
+static int ebcnt;
+static int pgcnt;
+static int errcnt;
+static struct rnd_state rnd_state;
+
+static inline void clear_data(unsigned char *buf, size_t len)
+{
+	memset(buf, 0, len);
+}
+
+static int write_eraseblock(int ebnum)
+{
+	size_t written;
+	int err = 0;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
+
+	prandom_bytes_state(&rnd_state, writebuf, subpgsize);
+	err = mtd_write(mtd, addr, subpgsize, &written, writebuf);
+	if (unlikely(err || written != subpgsize)) {
+		pr_err("error: write failed at %#llx\n",
+		       (long long)addr);
+		if (written != subpgsize) {
+			pr_err("  write size: %#x\n", subpgsize);
+			pr_err("  written: %#zx\n", written);
+		}
+		return err ? err : -1;
+	}
+
+	addr += subpgsize;
+
+	prandom_bytes_state(&rnd_state, writebuf, subpgsize);
+	err = mtd_write(mtd, addr, subpgsize, &written, writebuf);
+	if (unlikely(err || written != subpgsize)) {
+		pr_err("error: write failed at %#llx\n",
+		       (long long)addr);
+		if (written != subpgsize) {
+			pr_err("  write size: %#x\n", subpgsize);
+			pr_err("  written: %#zx\n", written);
+		}
+		return err ? err : -1;
+	}
+
+	return err;
+}
+
+static int write_eraseblock2(int ebnum)
+{
+	size_t written;
+	int err = 0, k;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
+
+	for (k = 1; k < 33; ++k) {
+		if (addr + (subpgsize * k) > (loff_t)(ebnum + 1) * mtd->erasesize)
+			break;
+		prandom_bytes_state(&rnd_state, writebuf, subpgsize * k);
+		err = mtd_write(mtd, addr, subpgsize * k, &written, writebuf);
+		if (unlikely(err || written != subpgsize * k)) {
+			pr_err("error: write failed at %#llx\n",
+			       (long long)addr);
+			if (written != subpgsize * k) {
+				pr_err("  write size: %#x\n",
+				       subpgsize * k);
+				pr_err("  written: %#08zx\n",
+				       written);
+			}
+			return err ? err : -1;
+		}
+		addr += subpgsize * k;
+	}
+
+	return err;
+}
+
+static void print_subpage(unsigned char *p)
+{
+	int i, j;
+
+	for (i = 0; i < subpgsize; ) {
+		for (j = 0; i < subpgsize && j < 32; ++i, ++j)
+			printk("%02x", *p++);
+		printk("\n");
+	}
+}
+
+static int verify_eraseblock(int ebnum)
+{
+	size_t read;
+	int err = 0;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
+
+	prandom_bytes_state(&rnd_state, writebuf, subpgsize);
+	clear_data(readbuf, subpgsize);
+	err = mtd_read(mtd, addr, subpgsize, &read, readbuf);
+	if (unlikely(err || read != subpgsize)) {
+		if (mtd_is_bitflip(err) && read == subpgsize) {
+			pr_info("ECC correction at %#llx\n",
+			       (long long)addr);
+			err = 0;
+		} else {
+			pr_err("error: read failed at %#llx\n",
+			       (long long)addr);
+			return err ? err : -1;
+		}
+	}
+	if (unlikely(memcmp(readbuf, writebuf, subpgsize))) {
+		pr_err("error: verify failed at %#llx\n",
+		       (long long)addr);
+		pr_info("------------- written----------------\n");
+		print_subpage(writebuf);
+		pr_info("------------- read ------------------\n");
+		print_subpage(readbuf);
+		pr_info("-------------------------------------\n");
+		errcnt += 1;
+	}
+
+	addr += subpgsize;
+
+	prandom_bytes_state(&rnd_state, writebuf, subpgsize);
+	clear_data(readbuf, subpgsize);
+	err = mtd_read(mtd, addr, subpgsize, &read, readbuf);
+	if (unlikely(err || read != subpgsize)) {
+		if (mtd_is_bitflip(err) && read == subpgsize) {
+			pr_info("ECC correction at %#llx\n",
+			       (long long)addr);
+			err = 0;
+		} else {
+			pr_err("error: read failed at %#llx\n",
+			       (long long)addr);
+			return err ? err : -1;
+		}
+	}
+	if (unlikely(memcmp(readbuf, writebuf, subpgsize))) {
+		pr_info("error: verify failed at %#llx\n",
+		       (long long)addr);
+		pr_info("------------- written----------------\n");
+		print_subpage(writebuf);
+		pr_info("------------- read ------------------\n");
+		print_subpage(readbuf);
+		pr_info("-------------------------------------\n");
+		errcnt += 1;
+	}
+
+	return err;
+}
+
+static int verify_eraseblock2(int ebnum)
+{
+	size_t read;
+	int err = 0, k;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
+
+	for (k = 1; k < 33; ++k) {
+		if (addr + (subpgsize * k) > (loff_t)(ebnum + 1) * mtd->erasesize)
+			break;
+		prandom_bytes_state(&rnd_state, writebuf, subpgsize * k);
+		clear_data(readbuf, subpgsize * k);
+		err = mtd_read(mtd, addr, subpgsize * k, &read, readbuf);
+		if (unlikely(err || read != subpgsize * k)) {
+			if (mtd_is_bitflip(err) && read == subpgsize * k) {
+				pr_info("ECC correction at %#llx\n",
+				       (long long)addr);
+				err = 0;
+			} else {
+				pr_err("error: read failed at "
+				       "%#llx\n", (long long)addr);
+				return err ? err : -1;
+			}
+		}
+		if (unlikely(memcmp(readbuf, writebuf, subpgsize * k))) {
+			pr_err("error: verify failed at %#llx\n",
+			       (long long)addr);
+			errcnt += 1;
+		}
+		addr += subpgsize * k;
+	}
+
+	return err;
+}
+
+static int verify_eraseblock_ff(int ebnum)
+{
+	uint32_t j;
+	size_t read;
+	int err = 0;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
+
+	memset(writebuf, 0xff, subpgsize);
+	for (j = 0; j < mtd->erasesize / subpgsize; ++j) {
+		clear_data(readbuf, subpgsize);
+		err = mtd_read(mtd, addr, subpgsize, &read, readbuf);
+		if (unlikely(err || read != subpgsize)) {
+			if (mtd_is_bitflip(err) && read == subpgsize) {
+				pr_info("ECC correction at %#llx\n",
+				       (long long)addr);
+				err = 0;
+			} else {
+				pr_err("error: read failed at "
+				       "%#llx\n", (long long)addr);
+				return err ? err : -1;
+			}
+		}
+		if (unlikely(memcmp(readbuf, writebuf, subpgsize))) {
+			pr_err("error: verify 0xff failed at "
+			       "%#llx\n", (long long)addr);
+			errcnt += 1;
+		}
+		addr += subpgsize;
+	}
+
+	return err;
+}
+
+static int verify_all_eraseblocks_ff(void)
+{
+	int err;
+	unsigned int i;
+
+	pr_info("verifying all eraseblocks for 0xff\n");
+	for (i = 0; i < ebcnt; ++i) {
+		if (bbt[i])
+			continue;
+		err = verify_eraseblock_ff(i);
+		if (err)
+			return err;
+		if (i % 256 == 0)
+			pr_info("verified up to eraseblock %u\n", i);
+
+		err = mtdtest_relax();
+		if (err)
+			return err;
+	}
+	pr_info("verified %u eraseblocks\n", i);
+	return 0;
+}
+
+static int __init mtd_subpagetest_init(void)
+{
+	int err = 0;
+	uint32_t i;
+	uint64_t tmp;
+
+	printk(KERN_INFO "\n");
+	printk(KERN_INFO "=================================================\n");
+
+	if (dev < 0) {
+		pr_info("Please specify a valid mtd-device via module parameter\n");
+		pr_crit("CAREFUL: This test wipes all data on the specified MTD device!\n");
+		return -EINVAL;
+	}
+
+	pr_info("MTD device: %d\n", dev);
+
+	mtd = get_mtd_device(NULL, dev);
+	if (IS_ERR(mtd)) {
+		err = PTR_ERR(mtd);
+		pr_err("error: cannot get MTD device\n");
+		return err;
+	}
+
+	if (!mtd_type_is_nand(mtd)) {
+		pr_info("this test requires NAND flash\n");
+		goto out;
+	}
+
+	subpgsize = mtd->writesize >> mtd->subpage_sft;
+	tmp = mtd->size;
+	do_div(tmp, mtd->erasesize);
+	ebcnt = tmp;
+	pgcnt = mtd->erasesize / mtd->writesize;
+
+	pr_info("MTD device size %llu, eraseblock size %u, "
+	       "page size %u, subpage size %u, count of eraseblocks %u, "
+	       "pages per eraseblock %u, OOB size %u\n",
+	       (unsigned long long)mtd->size, mtd->erasesize,
+	       mtd->writesize, subpgsize, ebcnt, pgcnt, mtd->oobsize);
+
+	err = -ENOMEM;
+	bufsize = subpgsize * 32;
+	writebuf = kmalloc(bufsize, GFP_KERNEL);
+	if (!writebuf)
+		goto out;
+	readbuf = kmalloc(bufsize, GFP_KERNEL);
+	if (!readbuf)
+		goto out;
+	bbt = kzalloc(ebcnt, GFP_KERNEL);
+	if (!bbt)
+		goto out;
+
+	err = mtdtest_scan_for_bad_eraseblocks(mtd, bbt, 0, ebcnt);
+	if (err)
+		goto out;
+
+	err = mtdtest_erase_good_eraseblocks(mtd, bbt, 0, ebcnt);
+	if (err)
+		goto out;
+
+	pr_info("writing whole device\n");
+	prandom_seed_state(&rnd_state, 1);
+	for (i = 0; i < ebcnt; ++i) {
+		if (bbt[i])
+			continue;
+		err = write_eraseblock(i);
+		if (unlikely(err))
+			goto out;
+		if (i % 256 == 0)
+			pr_info("written up to eraseblock %u\n", i);
+
+		err = mtdtest_relax();
+		if (err)
+			goto out;
+	}
+	pr_info("written %u eraseblocks\n", i);
+
+	prandom_seed_state(&rnd_state, 1);
+	pr_info("verifying all eraseblocks\n");
+	for (i = 0; i < ebcnt; ++i) {
+		if (bbt[i])
+			continue;
+		err = verify_eraseblock(i);
+		if (unlikely(err))
+			goto out;
+		if (i % 256 == 0)
+			pr_info("verified up to eraseblock %u\n", i);
+
+		err = mtdtest_relax();
+		if (err)
+			goto out;
+	}
+	pr_info("verified %u eraseblocks\n", i);
+
+	err = mtdtest_erase_good_eraseblocks(mtd, bbt, 0, ebcnt);
+	if (err)
+		goto out;
+
+	err = verify_all_eraseblocks_ff();
+	if (err)
+		goto out;
+
+	/* Write all eraseblocks */
+	prandom_seed_state(&rnd_state, 3);
+	pr_info("writing whole device\n");
+	for (i = 0; i < ebcnt; ++i) {
+		if (bbt[i])
+			continue;
+		err = write_eraseblock2(i);
+		if (unlikely(err))
+			goto out;
+		if (i % 256 == 0)
+			pr_info("written up to eraseblock %u\n", i);
+
+		err = mtdtest_relax();
+		if (err)
+			goto out;
+	}
+	pr_info("written %u eraseblocks\n", i);
+
+	/* Check all eraseblocks */
+	prandom_seed_state(&rnd_state, 3);
+	pr_info("verifying all eraseblocks\n");
+	for (i = 0; i < ebcnt; ++i) {
+		if (bbt[i])
+			continue;
+		err = verify_eraseblock2(i);
+		if (unlikely(err))
+			goto out;
+		if (i % 256 == 0)
+			pr_info("verified up to eraseblock %u\n", i);
+
+		err = mtdtest_relax();
+		if (err)
+			goto out;
+	}
+	pr_info("verified %u eraseblocks\n", i);
+
+	err = mtdtest_erase_good_eraseblocks(mtd, bbt, 0, ebcnt);
+	if (err)
+		goto out;
+
+	err = verify_all_eraseblocks_ff();
+	if (err)
+		goto out;
+
+	pr_info("finished with %d errors\n", errcnt);
+
+out:
+	kfree(bbt);
+	kfree(readbuf);
+	kfree(writebuf);
+	put_mtd_device(mtd);
+	if (err)
+		pr_info("error %d occurred\n", err);
+	printk(KERN_INFO "=================================================\n");
+	return err;
+}
+module_init(mtd_subpagetest_init);
+
+static void __exit mtd_subpagetest_exit(void)
+{
+	return;
+}
+module_exit(mtd_subpagetest_exit);
+
+MODULE_DESCRIPTION("Subpage test module");
+MODULE_AUTHOR("Adrian Hunter");
+MODULE_LICENSE("GPL");