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, 362 insertions, 0 deletions

diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
new file mode 100644
index 000000000..65cbe06e3
--- /dev/null
+++ b/fs/gfs2/trans.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
+ * Copyright (C) 2004-2006 Red Hat, Inc.  All rights reserved.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/completion.h>
+#include <linux/buffer_head.h>
+#include <linux/kallsyms.h>
+#include <linux/gfs2_ondisk.h>
+
+#include "gfs2.h"
+#include "incore.h"
+#include "glock.h"
+#include "inode.h"
+#include "log.h"
+#include "lops.h"
+#include "meta_io.h"
+#include "trans.h"
+#include "util.h"
+#include "trace_gfs2.h"
+
+static void gfs2_print_trans(struct gfs2_sbd *sdp, const struct gfs2_trans *tr)
+{
+	fs_warn(sdp, "Transaction created at: %pSR\n", (void *)tr->tr_ip);
+	fs_warn(sdp, "blocks=%u revokes=%u reserved=%u touched=%u\n",
+		tr->tr_blocks, tr->tr_revokes, tr->tr_reserved,
+		test_bit(TR_TOUCHED, &tr->tr_flags));
+	fs_warn(sdp, "Buf %u/%u Databuf %u/%u Revoke %u\n",
+		tr->tr_num_buf_new, tr->tr_num_buf_rm,
+		tr->tr_num_databuf_new, tr->tr_num_databuf_rm,
+		tr->tr_num_revoke);
+}
+
+int __gfs2_trans_begin(struct gfs2_trans *tr, struct gfs2_sbd *sdp,
+		       unsigned int blocks, unsigned int revokes,
+		       unsigned long ip)
+{
+	unsigned int extra_revokes;
+
+	if (current->journal_info) {
+		gfs2_print_trans(sdp, current->journal_info);
+		BUG();
+	}
+	BUG_ON(blocks == 0 && revokes == 0);
+
+	if (gfs2_withdrawn(sdp))
+		return -EROFS;
+
+	tr->tr_ip = ip;
+	tr->tr_blocks = blocks;
+	tr->tr_revokes = revokes;
+	tr->tr_reserved = GFS2_LOG_FLUSH_MIN_BLOCKS;
+	if (blocks) {
+		/*
+		 * The reserved blocks are either used for data or metadata.
+		 * We can have mixed data and metadata, each with its own log
+		 * descriptor block; see calc_reserved().
+		 */
+		tr->tr_reserved += blocks + 1 + DIV_ROUND_UP(blocks - 1, databuf_limit(sdp));
+	}
+	INIT_LIST_HEAD(&tr->tr_databuf);
+	INIT_LIST_HEAD(&tr->tr_buf);
+	INIT_LIST_HEAD(&tr->tr_list);
+	INIT_LIST_HEAD(&tr->tr_ail1_list);
+	INIT_LIST_HEAD(&tr->tr_ail2_list);
+
+	if (gfs2_assert_warn(sdp, tr->tr_reserved <= sdp->sd_jdesc->jd_blocks))
+		return -EINVAL;
+
+	sb_start_intwrite(sdp->sd_vfs);
+
+	/*
+	 * Try the reservations under sd_log_flush_lock to prevent log flushes
+	 * from creating inconsistencies between the number of allocated and
+	 * reserved revokes.  If that fails, do a full-block allocation outside
+	 * of the lock to avoid stalling log flushes.  Then, allot the
+	 * appropriate number of blocks to revokes, use as many revokes locally
+	 * as needed, and "release" the surplus into the revokes pool.
+	 */
+
+	down_read(&sdp->sd_log_flush_lock);
+	if (unlikely(!test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags)))
+		goto out_not_live;
+	if (gfs2_log_try_reserve(sdp, tr, &extra_revokes))
+		goto reserved;
+
+	up_read(&sdp->sd_log_flush_lock);
+	gfs2_log_reserve(sdp, tr, &extra_revokes);
+	down_read(&sdp->sd_log_flush_lock);
+	if (unlikely(!test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags))) {
+		revokes = tr->tr_revokes + extra_revokes;
+		gfs2_log_release_revokes(sdp, revokes);
+		gfs2_log_release(sdp, tr->tr_reserved);
+		goto out_not_live;
+	}
+
+reserved:
+	gfs2_log_release_revokes(sdp, extra_revokes);
+	current->journal_info = tr;
+	return 0;
+
+out_not_live:
+	up_read(&sdp->sd_log_flush_lock);
+	sb_end_intwrite(sdp->sd_vfs);
+	return -EROFS;
+}
+
+int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks,
+		     unsigned int revokes)
+{
+	struct gfs2_trans *tr;
+	int error;
+
+	tr = kmem_cache_zalloc(gfs2_trans_cachep, GFP_NOFS);
+	if (!tr)
+		return -ENOMEM;
+	error = __gfs2_trans_begin(tr, sdp, blocks, revokes, _RET_IP_);
+	if (error)
+		kmem_cache_free(gfs2_trans_cachep, tr);
+	return error;
+}
+
+void gfs2_trans_end(struct gfs2_sbd *sdp)
+{
+	struct gfs2_trans *tr = current->journal_info;
+	s64 nbuf;
+
+	current->journal_info = NULL;
+
+	if (!test_bit(TR_TOUCHED, &tr->tr_flags)) {
+		gfs2_log_release_revokes(sdp, tr->tr_revokes);
+		up_read(&sdp->sd_log_flush_lock);
+		gfs2_log_release(sdp, tr->tr_reserved);
+		if (!test_bit(TR_ONSTACK, &tr->tr_flags))
+			gfs2_trans_free(sdp, tr);
+		sb_end_intwrite(sdp->sd_vfs);
+		return;
+	}
+
+	gfs2_log_release_revokes(sdp, tr->tr_revokes - tr->tr_num_revoke);
+
+	nbuf = tr->tr_num_buf_new + tr->tr_num_databuf_new;
+	nbuf -= tr->tr_num_buf_rm;
+	nbuf -= tr->tr_num_databuf_rm;
+
+	if (gfs2_assert_withdraw(sdp, nbuf <= tr->tr_blocks) ||
+	    gfs2_assert_withdraw(sdp, tr->tr_num_revoke <= tr->tr_revokes))
+		gfs2_print_trans(sdp, tr);
+
+	gfs2_log_commit(sdp, tr);
+	if (!test_bit(TR_ONSTACK, &tr->tr_flags) &&
+	    !test_bit(TR_ATTACHED, &tr->tr_flags))
+		gfs2_trans_free(sdp, tr);
+	up_read(&sdp->sd_log_flush_lock);
+
+	if (sdp->sd_vfs->s_flags & SB_SYNCHRONOUS)
+		gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
+			       GFS2_LFC_TRANS_END);
+	sb_end_intwrite(sdp->sd_vfs);
+}
+
+static struct gfs2_bufdata *gfs2_alloc_bufdata(struct gfs2_glock *gl,
+					       struct buffer_head *bh)
+{
+	struct gfs2_bufdata *bd;
+
+	bd = kmem_cache_zalloc(gfs2_bufdata_cachep, GFP_NOFS | __GFP_NOFAIL);
+	bd->bd_bh = bh;
+	bd->bd_gl = gl;
+	INIT_LIST_HEAD(&bd->bd_list);
+	INIT_LIST_HEAD(&bd->bd_ail_st_list);
+	INIT_LIST_HEAD(&bd->bd_ail_gl_list);
+	return bd;
+}
+
+/**
+ * gfs2_trans_add_data - Add a databuf to the transaction.
+ * @gl: The inode glock associated with the buffer
+ * @bh: The buffer to add
+ *
+ * This is used in journaled data mode.
+ * We need to journal the data block in the same way as metadata in
+ * the functions above. The difference is that here we have a tag
+ * which is two __be64's being the block number (as per meta data)
+ * and a flag which says whether the data block needs escaping or
+ * not. This means we need a new log entry for each 251 or so data
+ * blocks, which isn't an enormous overhead but twice as much as
+ * for normal metadata blocks.
+ */
+void gfs2_trans_add_data(struct gfs2_glock *gl, struct buffer_head *bh)
+{
+	struct gfs2_trans *tr = current->journal_info;
+	struct gfs2_sbd *sdp = glock_sbd(gl);
+	struct gfs2_bufdata *bd;
+
+	lock_buffer(bh);
+	if (buffer_pinned(bh)) {
+		set_bit(TR_TOUCHED, &tr->tr_flags);
+		goto out;
+	}
+	spin_lock(&sdp->sd_log_lock);
+	bd = bh->b_private;
+	if (bd == NULL) {
+		spin_unlock(&sdp->sd_log_lock);
+		unlock_buffer(bh);
+		bd = gfs2_alloc_bufdata(gl, bh);
+		lock_buffer(bh);
+		spin_lock(&sdp->sd_log_lock);
+		if (bh->b_private) {
+			kmem_cache_free(gfs2_bufdata_cachep, bd);
+			bd = bh->b_private;
+		} else {
+			bh->b_private = bd;
+		}
+	}
+	gfs2_assert(sdp, bd->bd_gl == gl);
+	set_bit(TR_TOUCHED, &tr->tr_flags);
+	if (list_empty(&bd->bd_list)) {
+		set_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
+		set_bit(GLF_DIRTY, &bd->bd_gl->gl_flags);
+		gfs2_pin(sdp, bd->bd_bh);
+		tr->tr_num_databuf_new++;
+		list_add_tail(&bd->bd_list, &tr->tr_databuf);
+	}
+	spin_unlock(&sdp->sd_log_lock);
+out:
+	unlock_buffer(bh);
+}
+
+void gfs2_trans_add_databufs(struct gfs2_glock *gl, struct folio *folio,
+			     size_t from, size_t len)
+{
+	struct buffer_head *head = folio_buffers(folio);
+	unsigned int bsize = head->b_size;
+	struct buffer_head *bh;
+	size_t to = from + len;
+	size_t start, end;
+
+	for (bh = head, start = 0; bh != head || !start;
+	     bh = bh->b_this_page, start = end) {
+		end = start + bsize;
+		if (end <= from)
+			continue;
+		if (start >= to)
+			break;
+		set_buffer_uptodate(bh);
+		gfs2_trans_add_data(gl, bh);
+	}
+}
+
+void gfs2_trans_add_meta(struct gfs2_glock *gl, struct buffer_head *bh)
+{
+
+	struct gfs2_sbd *sdp = glock_sbd(gl);
+	struct super_block *sb = sdp->sd_vfs;
+	struct gfs2_bufdata *bd;
+	struct gfs2_meta_header *mh;
+	struct gfs2_trans *tr = current->journal_info;
+
+	lock_buffer(bh);
+	if (buffer_pinned(bh)) {
+		set_bit(TR_TOUCHED, &tr->tr_flags);
+		goto out;
+	}
+	spin_lock(&sdp->sd_log_lock);
+	bd = bh->b_private;
+	if (bd == NULL) {
+		spin_unlock(&sdp->sd_log_lock);
+		unlock_buffer(bh);
+		bd = gfs2_alloc_bufdata(gl, bh);
+		lock_buffer(bh);
+		spin_lock(&sdp->sd_log_lock);
+		if (bh->b_private) {
+			kmem_cache_free(gfs2_bufdata_cachep, bd);
+			bd = bh->b_private;
+		} else {
+			bh->b_private = bd;
+		}
+	}
+	gfs2_assert(sdp, bd->bd_gl == gl);
+	set_bit(TR_TOUCHED, &tr->tr_flags);
+	if (!list_empty(&bd->bd_list))
+		goto out_unlock;
+	set_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
+	set_bit(GLF_DIRTY, &bd->bd_gl->gl_flags);
+	mh = (struct gfs2_meta_header *)bd->bd_bh->b_data;
+	if (unlikely(mh->mh_magic != cpu_to_be32(GFS2_MAGIC))) {
+		fs_err(sdp, "Attempting to add uninitialised block to "
+		       "journal (inplace block=%lld)\n",
+		       (unsigned long long)bd->bd_bh->b_blocknr);
+		BUG();
+	}
+	if (gfs2_withdrawn(sdp)) {
+		fs_info(sdp, "GFS2:adding buf while withdrawn! 0x%llx\n",
+			(unsigned long long)bd->bd_bh->b_blocknr);
+		goto out_unlock;
+	}
+	if (unlikely(sb->s_writers.frozen == SB_FREEZE_COMPLETE)) {
+		fs_info(sdp, "GFS2:adding buf while frozen\n");
+		gfs2_withdraw(sdp);
+		goto out_unlock;
+	}
+	gfs2_pin(sdp, bd->bd_bh);
+	mh->__pad0 = cpu_to_be64(0);
+	mh->mh_jid = cpu_to_be32(sdp->sd_jdesc->jd_jid);
+	list_add(&bd->bd_list, &tr->tr_buf);
+	tr->tr_num_buf_new++;
+out_unlock:
+	spin_unlock(&sdp->sd_log_lock);
+out:
+	unlock_buffer(bh);
+}
+
+void gfs2_trans_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
+{
+	struct gfs2_trans *tr = current->journal_info;
+
+	BUG_ON(!list_empty(&bd->bd_list));
+	gfs2_add_revoke(sdp, bd);
+	set_bit(TR_TOUCHED, &tr->tr_flags);
+	tr->tr_num_revoke++;
+}
+
+void gfs2_trans_remove_revoke(struct gfs2_sbd *sdp, u64 blkno, unsigned int len)
+{
+	struct gfs2_bufdata *bd, *tmp;
+	unsigned int n = len;
+
+	spin_lock(&sdp->sd_log_lock);
+	list_for_each_entry_safe(bd, tmp, &sdp->sd_log_revokes, bd_list) {
+		if ((bd->bd_blkno >= blkno) && (bd->bd_blkno < (blkno + len))) {
+			list_del_init(&bd->bd_list);
+			gfs2_assert_withdraw(sdp, sdp->sd_log_num_revoke);
+			sdp->sd_log_num_revoke--;
+			if (bd->bd_gl)
+				gfs2_glock_remove_revoke(bd->bd_gl);
+			kmem_cache_free(gfs2_bufdata_cachep, bd);
+			gfs2_log_release_revokes(sdp, 1);
+			if (--n == 0)
+				break;
+		}
+	}
+	spin_unlock(&sdp->sd_log_lock);
+}
+
+void gfs2_trans_free(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
+{
+	if (tr == NULL)
+		return;
+
+	gfs2_assert_warn(sdp, list_empty(&tr->tr_ail1_list));
+	gfs2_assert_warn(sdp, list_empty(&tr->tr_ail2_list));
+	gfs2_assert_warn(sdp, list_empty(&tr->tr_databuf));
+	gfs2_assert_warn(sdp, list_empty(&tr->tr_buf));
+	kmem_cache_free(gfs2_trans_cachep, tr);
+}