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, 292 insertions, 0 deletions

diff --git a/fs/ntfs/bitmap.c b/fs/ntfs/bitmap.c
new file mode 100644
index 000000000..5a4457551
--- /dev/null
+++ b/fs/ntfs/bitmap.c
@@ -0,0 +1,292 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * NTFS kernel bitmap handling.
+ *
+ * Copyright (c) 2004-2005 Anton Altaparmakov
+ * Copyright (c) 2025 LG Electronics Co., Ltd.
+ */
+
+#include <linux/bitops.h>
+#include <linux/blkdev.h>
+
+#include "bitmap.h"
+#include "ntfs.h"
+
+int ntfs_trim_fs(struct ntfs_volume *vol, struct fstrim_range *range)
+{
+	size_t buf_clusters;
+	pgoff_t index, start_index, end_index;
+	struct file_ra_state *ra;
+	struct folio *folio;
+	unsigned long *bitmap;
+	char *kaddr;
+	u64 end, trimmed = 0, start_buf, end_buf, end_cluster;
+	u64 start_cluster = ntfs_bytes_to_cluster(vol, range->start);
+	u32 dq = bdev_discard_granularity(vol->sb->s_bdev);
+	int ret = 0;
+
+	if (!dq)
+		dq = vol->cluster_size;
+
+	if (start_cluster >= vol->nr_clusters)
+		return -EINVAL;
+
+	if (range->len == (u64)-1)
+		end_cluster = vol->nr_clusters;
+	else {
+		end_cluster = ntfs_bytes_to_cluster(vol,
+				(range->start + range->len + vol->cluster_size - 1));
+		if (end_cluster > vol->nr_clusters)
+			end_cluster = vol->nr_clusters;
+	}
+
+	ra = kzalloc_obj(*ra, GFP_NOFS);
+	if (!ra)
+		return -ENOMEM;
+
+	buf_clusters = PAGE_SIZE * 8;
+	start_index = start_cluster >> 15;
+	end_index = (end_cluster + buf_clusters - 1) >> 15;
+
+	for (index = start_index; index < end_index; index++) {
+		folio = ntfs_get_locked_folio(vol->lcnbmp_ino->i_mapping,
+				index, end_index, ra);
+		if (IS_ERR(folio)) {
+			ret = PTR_ERR(folio);
+			goto out_free;
+		}
+
+		kaddr = kmap_local_folio(folio, 0);
+		bitmap = (unsigned long *)kaddr;
+
+		start_buf = max_t(u64, index * buf_clusters, start_cluster);
+		end_buf = min_t(u64, (index + 1) * buf_clusters, end_cluster);
+
+		end = start_buf;
+		while (end < end_buf) {
+			u64 aligned_start, aligned_end, aligned_count;
+			u64 start = find_next_zero_bit(bitmap, end_buf - start_buf,
+					end - start_buf) + start_buf;
+			if (start >= end_buf)
+				break;
+
+			end = find_next_bit(bitmap, end_buf - start_buf,
+					start - start_buf) + start_buf;
+
+			aligned_start = ALIGN(ntfs_cluster_to_bytes(vol, start), dq);
+			aligned_end = ALIGN_DOWN(ntfs_cluster_to_bytes(vol, end), dq);
+			if (aligned_start >= aligned_end)
+				continue;
+			aligned_count = aligned_end - aligned_start;
+			if (aligned_count >= range->minlen) {
+				ret = blkdev_issue_discard(vol->sb->s_bdev, aligned_start >> 9,
+						aligned_count >> 9, GFP_NOFS);
+				if (ret)
+					goto out_unmap;
+				trimmed += aligned_count;
+			}
+		}
+
+out_unmap:
+		kunmap_local(kaddr);
+		folio_unlock(folio);
+		folio_put(folio);
+
+		if (ret)
+			goto out_free;
+	}
+
+	range->len = trimmed;
+
+out_free:
+	kfree(ra);
+	return ret;
+}
+
+/*
+ * __ntfs_bitmap_set_bits_in_run - set a run of bits in a bitmap to a value
+ * @vi:			vfs inode describing the bitmap
+ * @start_bit:		first bit to set
+ * @count:		number of bits to set
+ * @value:		value to set the bits to (i.e. 0 or 1)
+ * @is_rollback:	if 'true' this is a rollback operation
+ *
+ * Set @count bits starting at bit @start_bit in the bitmap described by the
+ * vfs inode @vi to @value, where @value is either 0 or 1.
+ *
+ * @is_rollback should always be 'false', it is for internal use to rollback
+ * errors.  You probably want to use ntfs_bitmap_set_bits_in_run() instead.
+ *
+ * Return 0 on success and -errno on error.
+ */
+int __ntfs_bitmap_set_bits_in_run(struct inode *vi, const s64 start_bit,
+		const s64 count, const u8 value, const bool is_rollback)
+{
+	s64 cnt = count;
+	pgoff_t index, end_index;
+	struct address_space *mapping;
+	struct folio *folio;
+	u8 *kaddr;
+	int pos, len, err;
+	u8 bit;
+	struct ntfs_inode *ni = NTFS_I(vi);
+	struct ntfs_volume *vol = ni->vol;
+
+	ntfs_debug("Entering for i_ino 0x%llx, start_bit 0x%llx, count 0x%llx, value %u.%s",
+			ni->mft_no, (unsigned long long)start_bit,
+			(unsigned long long)cnt, (unsigned int)value,
+			is_rollback ? " (rollback)" : "");
+
+	if (start_bit < 0 || cnt < 0 || value > 1)
+		return -EINVAL;
+
+	/*
+	 * Calculate the indices for the pages containing the first and last
+	 * bits, i.e. @start_bit and @start_bit + @cnt - 1, respectively.
+	 */
+	index = start_bit >> (3 + PAGE_SHIFT);
+	end_index = (start_bit + cnt - 1) >> (3 + PAGE_SHIFT);
+
+	/* Get the page containing the first bit (@start_bit). */
+	mapping = vi->i_mapping;
+	folio = read_mapping_folio(mapping, index, NULL);
+	if (IS_ERR(folio)) {
+		if (!is_rollback)
+			ntfs_error(vi->i_sb,
+				"Failed to map first page (error %li), aborting.",
+				PTR_ERR(folio));
+		return PTR_ERR(folio);
+	}
+
+	folio_lock(folio);
+	kaddr = kmap_local_folio(folio, 0);
+
+	/* Set @pos to the position of the byte containing @start_bit. */
+	pos = (start_bit >> 3) & ~PAGE_MASK;
+
+	/* Calculate the position of @start_bit in the first byte. */
+	bit = start_bit & 7;
+
+	/* If the first byte is partial, modify the appropriate bits in it. */
+	if (bit) {
+		u8 *byte = kaddr + pos;
+
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, min_t(s64, 8 - bit, cnt));
+		while ((bit & 7) && cnt) {
+			cnt--;
+			if (value)
+				*byte |= 1 << bit++;
+			else
+				*byte &= ~(1 << bit++);
+		}
+		/* If we are done, unmap the page and return success. */
+		if (!cnt)
+			goto done;
+
+		/* Update @pos to the new position. */
+		pos++;
+	}
+	/*
+	 * Depending on @value, modify all remaining whole bytes in the page up
+	 * to @cnt.
+	 */
+	len = min_t(s64, cnt >> 3, PAGE_SIZE - pos);
+	memset(kaddr + pos, value ? 0xff : 0, len);
+	cnt -= len << 3;
+	if (ni->mft_no == FILE_Bitmap)
+		ntfs_set_lcn_empty_bits(vol, index, value, len << 3);
+
+	/* Update @len to point to the first not-done byte in the page. */
+	if (cnt < 8)
+		len += pos;
+
+	/* If we are not in the last page, deal with all subsequent pages. */
+	while (index < end_index) {
+		if (cnt <= 0) {
+			err = -EIO;
+			goto rollback;
+		}
+
+		/* Update @index and get the next folio. */
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
+		kunmap_local(kaddr);
+		folio_put(folio);
+		folio = read_mapping_folio(mapping, ++index, NULL);
+		if (IS_ERR(folio)) {
+			ntfs_error(vi->i_sb,
+				   "Failed to map subsequent page (error %li), aborting.",
+				   PTR_ERR(folio));
+			err = PTR_ERR(folio);
+			goto rollback;
+		}
+
+		folio_lock(folio);
+		kaddr = kmap_local_folio(folio, 0);
+		/*
+		 * Depending on @value, modify all remaining whole bytes in the
+		 * page up to @cnt.
+		 */
+		len = min_t(s64, cnt >> 3, PAGE_SIZE);
+		memset(kaddr, value ? 0xff : 0, len);
+		cnt -= len << 3;
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, len << 3);
+	}
+	/*
+	 * The currently mapped page is the last one.  If the last byte is
+	 * partial, modify the appropriate bits in it.  Note, @len is the
+	 * position of the last byte inside the page.
+	 */
+	if (cnt) {
+		u8 *byte;
+
+		WARN_ON(cnt > 7);
+
+		bit = cnt;
+		byte = kaddr + len;
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, bit);
+		while (bit--) {
+			if (value)
+				*byte |= 1 << bit;
+			else
+				*byte &= ~(1 << bit);
+		}
+	}
+done:
+	/* We are done.  Unmap the folio and return success. */
+	folio_mark_dirty(folio);
+	folio_unlock(folio);
+	kunmap_local(kaddr);
+	folio_put(folio);
+	ntfs_debug("Done.");
+	return 0;
+rollback:
+	/*
+	 * Current state:
+	 *	- no pages are mapped
+	 *	- @count - @cnt is the number of bits that have been modified
+	 */
+	if (is_rollback)
+		return err;
+	if (count != cnt)
+		pos = __ntfs_bitmap_set_bits_in_run(vi, start_bit, count - cnt,
+				value ? 0 : 1, true);
+	else
+		pos = 0;
+	if (!pos) {
+		/* Rollback was successful. */
+		ntfs_error(vi->i_sb,
+			"Failed to map subsequent page (error %i), aborting.",
+			err);
+	} else {
+		/* Rollback failed. */
+		ntfs_error(vi->i_sb,
+			"Failed to map subsequent page (error %i) and rollback failed (error %i). Aborting and leaving inconsistent metadata. Unmount and run chkdsk.",
+			err, pos);
+		NVolSetErrors(NTFS_SB(vi->i_sb));
+	}
+	return err;
+}