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, 380 insertions, 0 deletions

diff --git a/fs/omfs/file.c b/fs/omfs/file.c
new file mode 100644
index 000000000..28f3b1133
--- /dev/null
+++ b/fs/omfs/file.c
@@ -0,0 +1,380 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * OMFS (as used by RIO Karma) file operations.
+ * Copyright (C) 2005 Bob Copeland <me@bobcopeland.com>
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/mpage.h>
+#include "omfs.h"
+
+static u32 omfs_max_extents(struct omfs_sb_info *sbi, int offset)
+{
+	return (sbi->s_sys_blocksize - offset -
+		sizeof(struct omfs_extent)) /
+		sizeof(struct omfs_extent_entry);
+}
+
+void omfs_make_empty_table(struct buffer_head *bh, int offset)
+{
+	struct omfs_extent *oe = (struct omfs_extent *) &bh->b_data[offset];
+
+	oe->e_next = ~cpu_to_be64(0ULL);
+	oe->e_extent_count = cpu_to_be32(1),
+	oe->e_fill = cpu_to_be32(0x22),
+	oe->e_entry[0].e_cluster = ~cpu_to_be64(0ULL);
+	oe->e_entry[0].e_blocks = ~cpu_to_be64(0ULL);
+}
+
+int omfs_shrink_inode(struct inode *inode)
+{
+	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
+	struct omfs_extent *oe;
+	struct omfs_extent_entry *entry;
+	struct buffer_head *bh;
+	u64 next, last;
+	u32 extent_count;
+	u32 max_extents;
+	int ret;
+
+	/* traverse extent table, freeing each entry that is greater
+	 * than inode->i_size;
+	 */
+	next = inode->i_ino;
+
+	/* only support truncate -> 0 for now */
+	ret = -EIO;
+	if (inode->i_size != 0)
+		goto out;
+
+	bh = omfs_bread(inode->i_sb, next);
+	if (!bh)
+		goto out;
+
+	oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);
+	max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);
+
+	for (;;) {
+
+		if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next))
+			goto out_brelse;
+
+		extent_count = be32_to_cpu(oe->e_extent_count);
+
+		if (extent_count > max_extents)
+			goto out_brelse;
+
+		last = next;
+		next = be64_to_cpu(oe->e_next);
+		entry = oe->e_entry;
+
+		/* ignore last entry as it is the terminator */
+		for (; extent_count > 1; extent_count--) {
+			u64 start, count;
+			start = be64_to_cpu(entry->e_cluster);
+			count = be64_to_cpu(entry->e_blocks);
+
+			omfs_clear_range(inode->i_sb, start, (int) count);
+			entry++;
+		}
+		omfs_make_empty_table(bh, (char *) oe - bh->b_data);
+		mark_buffer_dirty(bh);
+		brelse(bh);
+
+		if (last != inode->i_ino)
+			omfs_clear_range(inode->i_sb, last, sbi->s_mirrors);
+
+		if (next == ~0)
+			break;
+
+		bh = omfs_bread(inode->i_sb, next);
+		if (!bh)
+			goto out;
+		oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);
+		max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);
+	}
+	ret = 0;
+out:
+	return ret;
+out_brelse:
+	brelse(bh);
+	return ret;
+}
+
+static void omfs_truncate(struct inode *inode)
+{
+	omfs_shrink_inode(inode);
+	mark_inode_dirty(inode);
+}
+
+/*
+ * Add new blocks to the current extent, or create new entries/continuations
+ * as necessary.
+ */
+static int omfs_grow_extent(struct inode *inode, struct omfs_extent *oe,
+			u64 *ret_block)
+{
+	struct omfs_extent_entry *terminator;
+	struct omfs_extent_entry *entry = oe->e_entry;
+	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
+	u32 extent_count = be32_to_cpu(oe->e_extent_count);
+	u64 new_block = 0;
+	u32 max_count;
+	int new_count;
+	int ret = 0;
+
+	/* reached the end of the extent table with no blocks mapped.
+	 * there are three possibilities for adding: grow last extent,
+	 * add a new extent to the current extent table, and add a
+	 * continuation inode.  in last two cases need an allocator for
+	 * sbi->s_cluster_size
+	 */
+
+	/* TODO: handle holes */
+
+	/* should always have a terminator */
+	if (extent_count < 1)
+		return -EIO;
+
+	/* trivially grow current extent, if next block is not taken */
+	terminator = entry + extent_count - 1;
+	if (extent_count > 1) {
+		entry = terminator-1;
+		new_block = be64_to_cpu(entry->e_cluster) +
+			be64_to_cpu(entry->e_blocks);
+
+		if (omfs_allocate_block(inode->i_sb, new_block)) {
+			be64_add_cpu(&entry->e_blocks, 1);
+			terminator->e_blocks = ~(cpu_to_be64(
+				be64_to_cpu(~terminator->e_blocks) + 1));
+			goto out;
+		}
+	}
+	max_count = omfs_max_extents(sbi, OMFS_EXTENT_START);
+
+	/* TODO: add a continuation block here */
+	if (be32_to_cpu(oe->e_extent_count) > max_count-1)
+		return -EIO;
+
+	/* try to allocate a new cluster */
+	ret = omfs_allocate_range(inode->i_sb, 1, sbi->s_clustersize,
+		&new_block, &new_count);
+	if (ret)
+		goto out_fail;
+
+	/* copy terminator down an entry */
+	entry = terminator;
+	terminator++;
+	memcpy(terminator, entry, sizeof(struct omfs_extent_entry));
+
+	entry->e_cluster = cpu_to_be64(new_block);
+	entry->e_blocks = cpu_to_be64((u64) new_count);
+
+	terminator->e_blocks = ~(cpu_to_be64(
+		be64_to_cpu(~terminator->e_blocks) + (u64) new_count));
+
+	/* write in new entry */
+	be32_add_cpu(&oe->e_extent_count, 1);
+
+out:
+	*ret_block = new_block;
+out_fail:
+	return ret;
+}
+
+/*
+ * Scans across the directory table for a given file block number.
+ * If block not found, return 0.
+ */
+static sector_t find_block(struct inode *inode, struct omfs_extent_entry *ent,
+			sector_t block, int count, int *left)
+{
+	/* count > 1 because of terminator */
+	sector_t searched = 0;
+	for (; count > 1; count--) {
+		int numblocks = clus_to_blk(OMFS_SB(inode->i_sb),
+			be64_to_cpu(ent->e_blocks));
+
+		if (block >= searched  &&
+		    block < searched + numblocks) {
+			/*
+			 * found it at cluster + (block - searched)
+			 * numblocks - (block - searched) is remainder
+			 */
+			*left = numblocks - (block - searched);
+			return clus_to_blk(OMFS_SB(inode->i_sb),
+				be64_to_cpu(ent->e_cluster)) +
+				block - searched;
+		}
+		searched += numblocks;
+		ent++;
+	}
+	return 0;
+}
+
+static int omfs_get_block(struct inode *inode, sector_t block,
+			  struct buffer_head *bh_result, int create)
+{
+	struct buffer_head *bh;
+	sector_t next, offset;
+	int ret;
+	u64 new_block;
+	u32 max_extents;
+	int extent_count;
+	struct omfs_extent *oe;
+	struct omfs_extent_entry *entry;
+	struct omfs_sb_info *sbi = OMFS_SB(inode->i_sb);
+	int max_blocks = bh_result->b_size >> inode->i_blkbits;
+	int remain;
+
+	ret = -EIO;
+	bh = omfs_bread(inode->i_sb, inode->i_ino);
+	if (!bh)
+		goto out;
+
+	oe = (struct omfs_extent *)(&bh->b_data[OMFS_EXTENT_START]);
+	max_extents = omfs_max_extents(sbi, OMFS_EXTENT_START);
+	next = inode->i_ino;
+
+	for (;;) {
+
+		if (omfs_is_bad(sbi, (struct omfs_header *) bh->b_data, next))
+			goto out_brelse;
+
+		extent_count = be32_to_cpu(oe->e_extent_count);
+		next = be64_to_cpu(oe->e_next);
+		entry = oe->e_entry;
+
+		if (extent_count > max_extents)
+			goto out_brelse;
+
+		offset = find_block(inode, entry, block, extent_count, &remain);
+		if (offset > 0) {
+			ret = 0;
+			map_bh(bh_result, inode->i_sb, offset);
+			if (remain > max_blocks)
+				remain = max_blocks;
+			bh_result->b_size = (remain << inode->i_blkbits);
+			goto out_brelse;
+		}
+		if (next == ~0)
+			break;
+
+		brelse(bh);
+		bh = omfs_bread(inode->i_sb, next);
+		if (!bh)
+			goto out;
+		oe = (struct omfs_extent *) (&bh->b_data[OMFS_EXTENT_CONT]);
+		max_extents = omfs_max_extents(sbi, OMFS_EXTENT_CONT);
+	}
+	if (create) {
+		ret = omfs_grow_extent(inode, oe, &new_block);
+		if (ret == 0) {
+			mark_buffer_dirty(bh);
+			mark_inode_dirty(inode);
+			map_bh(bh_result, inode->i_sb,
+					clus_to_blk(sbi, new_block));
+		}
+	}
+out_brelse:
+	brelse(bh);
+out:
+	return ret;
+}
+
+static int omfs_read_folio(struct file *file, struct folio *folio)
+{
+	return block_read_full_folio(folio, omfs_get_block);
+}
+
+static void omfs_readahead(struct readahead_control *rac)
+{
+	mpage_readahead(rac, omfs_get_block);
+}
+
+static int
+omfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
+{
+	return mpage_writepages(mapping, wbc, omfs_get_block);
+}
+
+static void omfs_write_failed(struct address_space *mapping, loff_t to)
+{
+	struct inode *inode = mapping->host;
+
+	if (to > inode->i_size) {
+		truncate_pagecache(inode, inode->i_size);
+		omfs_truncate(inode);
+	}
+}
+
+static int omfs_write_begin(const struct kiocb *iocb,
+			    struct address_space *mapping,
+			    loff_t pos, unsigned len,
+			    struct folio **foliop, void **fsdata)
+{
+	int ret;
+
+	ret = block_write_begin(mapping, pos, len, foliop, omfs_get_block);
+	if (unlikely(ret))
+		omfs_write_failed(mapping, pos + len);
+
+	return ret;
+}
+
+static sector_t omfs_bmap(struct address_space *mapping, sector_t block)
+{
+	return generic_block_bmap(mapping, block, omfs_get_block);
+}
+
+const struct file_operations omfs_file_operations = {
+	.llseek = generic_file_llseek,
+	.read_iter = generic_file_read_iter,
+	.write_iter = generic_file_write_iter,
+	.mmap_prepare = generic_file_mmap_prepare,
+	.fsync = simple_fsync,
+	.splice_read = filemap_splice_read,
+};
+
+static int omfs_setattr(struct mnt_idmap *idmap,
+			struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = d_inode(dentry);
+	int error;
+
+	error = setattr_prepare(&nop_mnt_idmap, dentry, attr);
+	if (error)
+		return error;
+
+	if ((attr->ia_valid & ATTR_SIZE) &&
+	    attr->ia_size != i_size_read(inode)) {
+		error = inode_newsize_ok(inode, attr->ia_size);
+		if (error)
+			return error;
+		truncate_setsize(inode, attr->ia_size);
+		omfs_truncate(inode);
+	}
+
+	setattr_copy(&nop_mnt_idmap, inode, attr);
+	mark_inode_dirty(inode);
+	return 0;
+}
+
+const struct inode_operations omfs_file_inops = {
+	.setattr = omfs_setattr,
+};
+
+const struct address_space_operations omfs_aops = {
+	.dirty_folio = block_dirty_folio,
+	.invalidate_folio = block_invalidate_folio,
+	.read_folio = omfs_read_folio,
+	.readahead = omfs_readahead,
+	.writepages = omfs_writepages,
+	.write_begin = omfs_write_begin,
+	.write_end = generic_write_end,
+	.bmap = omfs_bmap,
+	.migrate_folio = buffer_migrate_folio,
+};
+