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, 459 insertions, 0 deletions

diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
new file mode 100644
index 000000000..ccd136301
--- /dev/null
+++ b/fs/exfat/inode.c
@@ -0,0 +1,459 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
+ */
+
+#include <linux/init.h>
+#include <linux/buffer_head.h>
+#include <linux/mpage.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/time.h>
+#include <linux/writeback.h>
+#include <linux/uio.h>
+#include <linux/random.h>
+#include <linux/iversion.h>
+#include <linux/iomap.h>
+
+#include "exfat_raw.h"
+#include "exfat_fs.h"
+#include "iomap.h"
+
+int __exfat_write_inode(struct inode *inode, int sync)
+{
+	unsigned long long on_disk_size;
+	unsigned long long on_disk_valid_size;
+	struct exfat_dentry *ep, *ep2;
+	struct exfat_entry_set_cache es;
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	bool is_dir = (ei->type == TYPE_DIR);
+	struct timespec64 ts;
+
+	if (inode->i_ino == EXFAT_ROOT_INO)
+		return 0;
+
+	/*
+	 * If the inode is already unlinked, there is no need for updating it.
+	 */
+	if (ei->dir.dir == DIR_DELETED)
+		return 0;
+
+	if (is_dir && ei->dir.dir == sbi->root_dir && ei->entry == -1)
+		return 0;
+
+	exfat_set_volume_dirty(sb);
+
+	/* get the directory entry of given file or directory */
+	if (exfat_get_dentry_set_by_ei(&es, sb, ei))
+		return -EIO;
+	ep = exfat_get_dentry_cached(&es, ES_IDX_FILE);
+	ep2 = exfat_get_dentry_cached(&es, ES_IDX_STREAM);
+
+	ep->dentry.file.attr = cpu_to_le16(exfat_make_attr(inode));
+
+	/* set FILE_INFO structure using the acquired struct exfat_dentry */
+	exfat_set_entry_time(sbi, &ei->i_crtime,
+			&ep->dentry.file.create_tz,
+			&ep->dentry.file.create_time,
+			&ep->dentry.file.create_date,
+			&ep->dentry.file.create_time_cs);
+	ts = inode_get_mtime(inode);
+	exfat_set_entry_time(sbi, &ts,
+			     &ep->dentry.file.modify_tz,
+			     &ep->dentry.file.modify_time,
+			     &ep->dentry.file.modify_date,
+			     &ep->dentry.file.modify_time_cs);
+	ts = inode_get_atime(inode);
+	exfat_set_entry_time(sbi, &ts,
+			     &ep->dentry.file.access_tz,
+			     &ep->dentry.file.access_time,
+			     &ep->dentry.file.access_date,
+			     NULL);
+
+	/*
+	 * During a DIO write, valid_size is updated eagerly in iomap_end (so
+	 * that concurrent buffered reads see IOMAP_MAPPED) while i_size is
+	 * updated asynchronously in end_io.  The FAT chain was already
+	 * extended to cover ceil(valid_size/cluster_size) clusters.  Use the
+	 * maximum so the on-disk size field always covers the FAT chain,
+	 * preventing fsck from reporting "more clusters are allocated".
+	 */
+	on_disk_size = max_t(unsigned long long, i_size_read(inode),
+			ei->valid_size);
+
+	if (ei->start_clu == EXFAT_EOF_CLUSTER)
+		on_disk_size = 0;
+	/*
+	 * valid_size on disk must reflect only confirmed data (up to i_size)
+	 * and must not exceed on_disk_size.
+	 */
+	on_disk_valid_size = min_t(unsigned long long, ei->valid_size,
+			i_size_read(inode));
+	if (ei->start_clu == EXFAT_EOF_CLUSTER)
+		on_disk_valid_size = 0;
+
+	ep2->dentry.stream.size = cpu_to_le64(on_disk_size);
+	ep2->dentry.stream.valid_size = cpu_to_le64(on_disk_valid_size);
+
+	if (on_disk_size) {
+		ep2->dentry.stream.flags = ei->flags;
+		ep2->dentry.stream.start_clu = cpu_to_le32(ei->start_clu);
+	} else {
+		ep2->dentry.stream.flags = ALLOC_FAT_CHAIN;
+		ep2->dentry.stream.start_clu = EXFAT_FREE_CLUSTER;
+	}
+
+	exfat_update_dir_chksum(&es);
+	return exfat_put_dentry_set(&es, sync);
+}
+
+int exfat_write_inode(struct inode *inode, struct writeback_control *wbc)
+{
+	int ret;
+
+	if (unlikely(exfat_forced_shutdown(inode->i_sb)))
+		return -EIO;
+
+	mutex_lock(&EXFAT_SB(inode->i_sb)->s_lock);
+	ret = __exfat_write_inode(inode, wbc->sync_mode == WB_SYNC_ALL);
+	mutex_unlock(&EXFAT_SB(inode->i_sb)->s_lock);
+
+	return ret;
+}
+
+void exfat_sync_inode(struct inode *inode)
+{
+	lockdep_assert_held(&EXFAT_SB(inode->i_sb)->s_lock);
+	__exfat_write_inode(inode, 1);
+}
+
+/*
+ * Input: inode, (logical) clu_offset, target allocation area
+ * Output: errcode, cluster number
+ * *clu = (~0), if it's unable to allocate a new cluster
+ */
+int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
+		unsigned int *clu, unsigned int *count, int create,
+		bool *balloc)
+{
+	int ret;
+	unsigned int last_clu;
+	struct exfat_chain new_clu;
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	unsigned int local_clu_offset = clu_offset;
+	unsigned int num_to_be_allocated = 0, num_clusters;
+
+	num_clusters = exfat_bytes_to_cluster(sbi, exfat_ondisk_size(inode));
+	if (clu_offset > num_clusters ||
+	    *count > num_clusters - clu_offset)
+		num_to_be_allocated = clu_offset + *count - num_clusters;
+
+	if (!create && (num_to_be_allocated > 0)) {
+		*clu = EXFAT_EOF_CLUSTER;
+		return 0;
+	}
+
+	*clu = last_clu = ei->start_clu;
+
+	if (*clu == EXFAT_EOF_CLUSTER) {
+		*count = 0;
+	} else if (ei->flags == ALLOC_NO_FAT_CHAIN) {
+		last_clu += num_clusters - 1;
+		if (clu_offset < num_clusters) {
+			*clu += clu_offset;
+			*count = min(num_clusters - clu_offset, *count);
+		} else {
+			*clu = EXFAT_EOF_CLUSTER;
+			*count = 0;
+		}
+	} else {
+		int err = exfat_get_cluster(inode, clu_offset,
+				clu, count, &last_clu);
+		if (err)
+			return -EIO;
+	}
+
+	if (*clu == EXFAT_EOF_CLUSTER) {
+		exfat_set_volume_dirty(sb);
+
+		new_clu.dir = (last_clu == EXFAT_EOF_CLUSTER) ?
+				EXFAT_EOF_CLUSTER : last_clu + 1;
+		new_clu.size = 0;
+		new_clu.flags = ei->flags;
+
+		/* allocate a cluster */
+		if (num_to_be_allocated < 1) {
+			/* Broken FAT (i_sze > allocated FAT) */
+			exfat_fs_error(sb, "broken FAT chain.");
+			return -EIO;
+		}
+
+		ret = exfat_alloc_cluster(inode, num_to_be_allocated, &new_clu,
+				inode_needs_sync(inode), true);
+		if (ret)
+			return ret;
+
+		if (new_clu.dir == EXFAT_EOF_CLUSTER ||
+		    new_clu.dir == EXFAT_FREE_CLUSTER) {
+			exfat_fs_error(sb,
+				"bogus cluster new allocated (last_clu : %u, new_clu : %u)",
+				last_clu, new_clu.dir);
+			return -EIO;
+		}
+
+		/* append to the FAT chain */
+		if (last_clu == EXFAT_EOF_CLUSTER) {
+			if (new_clu.flags == ALLOC_FAT_CHAIN)
+				ei->flags = ALLOC_FAT_CHAIN;
+			ei->start_clu = new_clu.dir;
+		} else {
+			if (new_clu.flags != ei->flags) {
+				/* no-fat-chain bit is disabled,
+				 * so fat-chain should be synced with
+				 * alloc-bitmap
+				 */
+				if (exfat_chain_cont_cluster(sb, ei->start_clu,
+						num_clusters))
+					return -EIO;
+				ei->flags = ALLOC_FAT_CHAIN;
+			}
+			if (new_clu.flags == ALLOC_FAT_CHAIN)
+				if (exfat_ent_set(sb, last_clu, new_clu.dir))
+					return -EIO;
+		}
+
+		*clu = new_clu.dir;
+		*count = new_clu.size;
+
+		inode->i_blocks += exfat_cluster_to_sectors(sbi, new_clu.size);
+		if (balloc)
+			*balloc = true;
+	}
+
+	/* hint information */
+	ei->hint_bmap.off = local_clu_offset;
+	ei->hint_bmap.clu = *clu;
+
+	return 0;
+}
+
+static int exfat_read_folio(struct file *file, struct folio *folio)
+{
+	struct iomap_read_folio_ctx ctx = {
+		.cur_folio = folio,
+		.ops = &exfat_iomap_bio_read_ops,
+	};
+
+	iomap_read_folio(&exfat_iomap_ops, &ctx, NULL);
+	return 0;
+}
+
+static void exfat_readahead(struct readahead_control *rac)
+{
+	struct address_space *mapping = rac->mapping;
+	struct inode *inode = mapping->host;
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t pos = readahead_pos(rac);
+	struct iomap_read_folio_ctx ctx = {
+		.ops = &exfat_iomap_bio_read_ops,
+		.rac = rac,
+	};
+
+	/* Range cross valid_size, read it page by page. */
+	if (ei->valid_size < i_size_read(inode) &&
+	    pos <= ei->valid_size &&
+	    ei->valid_size < pos + readahead_length(rac))
+		return;
+
+	iomap_readahead(&exfat_iomap_ops, &ctx, NULL);
+}
+
+static int exfat_writepages(struct address_space *mapping,
+		struct writeback_control *wbc)
+{
+	struct iomap_writepage_ctx wpc = {
+		.inode		= mapping->host,
+		.wbc		= wbc,
+		.ops		= &exfat_writeback_ops,
+	};
+
+	if (unlikely(exfat_forced_shutdown(mapping->host->i_sb)))
+		return -EIO;
+
+	return iomap_writepages(&wpc);
+}
+
+static sector_t exfat_aop_bmap(struct address_space *mapping, sector_t block)
+{
+	sector_t blocknr;
+
+	inode_lock_shared(mapping->host);
+	blocknr = iomap_bmap(mapping, block, &exfat_iomap_ops);
+	inode_unlock_shared(mapping->host);
+	return blocknr;
+}
+
+static const struct address_space_operations exfat_aops = {
+	.read_folio		= exfat_read_folio,
+	.readahead		= exfat_readahead,
+	.writepages		= exfat_writepages,
+	.dirty_folio		= iomap_dirty_folio,
+	.bmap			= exfat_aop_bmap,
+	.migrate_folio		= filemap_migrate_folio,
+	.is_partially_uptodate	= iomap_is_partially_uptodate,
+	.error_remove_folio	= generic_error_remove_folio,
+	.release_folio		= iomap_release_folio,
+	.invalidate_folio	= iomap_invalidate_folio,
+	.swap_activate		= exfat_iomap_swap_activate,
+};
+
+static inline unsigned long exfat_hash(loff_t i_pos)
+{
+	return hash_32(i_pos, EXFAT_HASH_BITS);
+}
+
+void exfat_hash_inode(struct inode *inode, loff_t i_pos)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(inode->i_sb);
+	struct hlist_head *head = sbi->inode_hashtable + exfat_hash(i_pos);
+
+	spin_lock(&sbi->inode_hash_lock);
+	EXFAT_I(inode)->i_pos = i_pos;
+	hlist_add_head(&EXFAT_I(inode)->i_hash_fat, head);
+	spin_unlock(&sbi->inode_hash_lock);
+}
+
+void exfat_unhash_inode(struct inode *inode)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(inode->i_sb);
+
+	spin_lock(&sbi->inode_hash_lock);
+	hlist_del_init(&EXFAT_I(inode)->i_hash_fat);
+	EXFAT_I(inode)->i_pos = 0;
+	spin_unlock(&sbi->inode_hash_lock);
+}
+
+struct inode *exfat_iget(struct super_block *sb, loff_t i_pos)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_inode_info *info;
+	struct hlist_head *head = sbi->inode_hashtable + exfat_hash(i_pos);
+	struct inode *inode = NULL;
+
+	spin_lock(&sbi->inode_hash_lock);
+	hlist_for_each_entry(info, head, i_hash_fat) {
+		WARN_ON(info->vfs_inode.i_sb != sb);
+
+		if (i_pos != info->i_pos)
+			continue;
+		inode = igrab(&info->vfs_inode);
+		if (inode)
+			break;
+	}
+	spin_unlock(&sbi->inode_hash_lock);
+	return inode;
+}
+
+/* doesn't deal with root inode */
+static int exfat_fill_inode(struct inode *inode, struct exfat_dir_entry *info)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(inode->i_sb);
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	loff_t size = info->size;
+
+	ei->dir = info->dir;
+	ei->entry = info->entry;
+	ei->attr = info->attr;
+	ei->start_clu = info->start_clu;
+	ei->flags = info->flags;
+	ei->type = info->type;
+	ei->valid_size = info->valid_size;
+	ei->zeroed_size = info->valid_size;
+
+	ei->version = 0;
+	ei->hint_stat.eidx = 0;
+	ei->hint_stat.clu = info->start_clu;
+	ei->hint_femp.eidx = EXFAT_HINT_NONE;
+	ei->hint_bmap.off = EXFAT_EOF_CLUSTER;
+	ei->i_pos = 0;
+
+	inode->i_uid = sbi->options.fs_uid;
+	inode->i_gid = sbi->options.fs_gid;
+	inode_inc_iversion(inode);
+	inode->i_generation = get_random_u32();
+
+	if (info->attr & EXFAT_ATTR_SUBDIR) { /* directory */
+		inode->i_generation &= ~1;
+		inode->i_mode = exfat_make_mode(sbi, info->attr, 0777);
+		inode->i_op = &exfat_dir_inode_operations;
+		inode->i_fop = &exfat_dir_operations;
+		set_nlink(inode, info->num_subdirs);
+	} else { /* regular file */
+		inode->i_generation |= 1;
+		inode->i_mode = exfat_make_mode(sbi, info->attr, 0777);
+		inode->i_op = &exfat_file_inode_operations;
+		inode->i_fop = &exfat_file_operations;
+		inode->i_mapping->a_ops = &exfat_aops;
+		inode->i_mapping->nrpages = 0;
+	}
+
+	i_size_write(inode, size);
+
+	exfat_save_attr(inode, info->attr);
+
+	inode->i_blocks = round_up(i_size_read(inode), sbi->cluster_size) >> 9;
+	inode_set_mtime_to_ts(inode, info->mtime);
+	inode_set_ctime_to_ts(inode, info->mtime);
+	ei->i_crtime = info->crtime;
+	inode_set_atime_to_ts(inode, info->atime);
+
+	return 0;
+}
+
+struct inode *exfat_build_inode(struct super_block *sb,
+		struct exfat_dir_entry *info, loff_t i_pos)
+{
+	struct inode *inode;
+	int err;
+
+	inode = exfat_iget(sb, i_pos);
+	if (inode)
+		goto out;
+	inode = new_inode(sb);
+	if (!inode) {
+		inode = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+	inode->i_ino = iunique(sb, EXFAT_ROOT_INO);
+	inode_set_iversion(inode, 1);
+	err = exfat_fill_inode(inode, info);
+	if (err) {
+		iput(inode);
+		inode = ERR_PTR(err);
+		goto out;
+	}
+	exfat_hash_inode(inode, i_pos);
+	insert_inode_hash(inode);
+out:
+	return inode;
+}
+
+void exfat_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+
+	if (!inode->i_nlink) {
+		i_size_write(inode, 0);
+		mutex_lock(&EXFAT_SB(inode->i_sb)->s_lock);
+		__exfat_truncate(inode);
+		mutex_unlock(&EXFAT_SB(inode->i_sb)->s_lock);
+	}
+
+	clear_inode(inode);
+	exfat_cache_inval_inode(inode);
+	exfat_unhash_inode(inode);
+}