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, 226 insertions, 0 deletions

diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
new file mode 100644
index 000000000..57c204a3c
--- /dev/null
+++ b/fs/afs/mntpt.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* mountpoint management
+ *
+ * Copyright (C) 2002 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/gfp.h>
+#include <linux/fs_context.h>
+#include "internal.h"
+
+
+static struct dentry *afs_mntpt_lookup(struct inode *dir,
+				       struct dentry *dentry,
+				       unsigned int flags);
+static int afs_mntpt_open(struct inode *inode, struct file *file);
+static void afs_mntpt_expiry_timed_out(struct work_struct *work);
+
+const struct file_operations afs_mntpt_file_operations = {
+	.open		= afs_mntpt_open,
+	.llseek		= noop_llseek,
+};
+
+const struct inode_operations afs_mntpt_inode_operations = {
+	.lookup		= afs_mntpt_lookup,
+	.readlink	= afs_readlink,
+	.getattr	= afs_getattr,
+};
+
+const struct inode_operations afs_autocell_inode_operations = {
+	.getattr	= afs_getattr,
+};
+
+static LIST_HEAD(afs_vfsmounts);
+static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
+
+static unsigned long afs_mntpt_expiry_timeout = 10 * 60;
+
+static const char afs_root_volume[] = "root.cell";
+
+/*
+ * no valid lookup procedure on this sort of dir
+ */
+static struct dentry *afs_mntpt_lookup(struct inode *dir,
+				       struct dentry *dentry,
+				       unsigned int flags)
+{
+	_enter("%p,%p{%pd2}", dir, dentry, dentry);
+	return ERR_PTR(-EREMOTE);
+}
+
+/*
+ * no valid open procedure on this sort of dir
+ */
+static int afs_mntpt_open(struct inode *inode, struct file *file)
+{
+	_enter("%p,%p{%pD2}", inode, file, file);
+	return -EREMOTE;
+}
+
+/*
+ * Set the parameters for the proposed superblock.
+ */
+static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
+{
+	struct afs_fs_context *ctx = fc->fs_private;
+	struct afs_super_info *src_as = AFS_FS_S(mntpt->d_sb);
+	struct afs_vnode *vnode = AFS_FS_I(d_inode(mntpt));
+	struct afs_cell *cell;
+	const char *p;
+	int ret;
+
+	if (fc->net_ns != src_as->net_ns) {
+		put_net(fc->net_ns);
+		fc->net_ns = get_net(src_as->net_ns);
+	}
+
+	if (src_as->volume && src_as->volume->type == AFSVL_RWVOL) {
+		ctx->type = AFSVL_RWVOL;
+		ctx->force = true;
+	}
+	if (ctx->cell) {
+		afs_unuse_cell(ctx->cell, afs_cell_trace_unuse_mntpt);
+		ctx->cell = NULL;
+	}
+	if (test_bit(AFS_VNODE_PSEUDODIR, &vnode->flags)) {
+		/* if the directory is a pseudo directory, use the d_name */
+		unsigned size = mntpt->d_name.len;
+
+		if (size < 2)
+			return -ENOENT;
+
+		p = mntpt->d_name.name;
+		if (mntpt->d_name.name[0] == '.') {
+			size--;
+			p++;
+			ctx->type = AFSVL_RWVOL;
+			ctx->force = true;
+		}
+		if (size > AFS_MAXCELLNAME)
+			return -ENAMETOOLONG;
+
+		cell = afs_lookup_cell(ctx->net, p, size, NULL,
+				       AFS_LOOKUP_CELL_MOUNTPOINT,
+				       afs_cell_trace_use_lookup_mntpt);
+		if (IS_ERR(cell)) {
+			pr_err("kAFS: unable to lookup cell '%pd'\n", mntpt);
+			return PTR_ERR(cell);
+		}
+		ctx->cell = cell;
+
+		ctx->volname = afs_root_volume;
+		ctx->volnamesz = sizeof(afs_root_volume) - 1;
+	} else {
+		/* read the contents of the AFS special symlink */
+		DEFINE_DELAYED_CALL(cleanup);
+		const char *content;
+		loff_t size = i_size_read(d_inode(mntpt));
+
+		if (src_as->cell)
+			ctx->cell = afs_use_cell(src_as->cell, afs_cell_trace_use_mntpt);
+
+		if (size < 2 || size > PAGE_SIZE - 1)
+			return -EINVAL;
+
+		content = afs_get_link(mntpt, d_inode(mntpt), &cleanup);
+		if (IS_ERR(content)) {
+			do_delayed_call(&cleanup);
+			return PTR_ERR(content);
+		}
+
+		ret = -EINVAL;
+		if (content[size - 1] == '.')
+			ret = vfs_parse_fs_qstr(fc, "source",
+						&QSTR_LEN(content, size - 1));
+		do_delayed_call(&cleanup);
+		if (ret < 0)
+			return ret;
+
+		/* Don't cross a backup volume mountpoint from a backup volume */
+		if (src_as->volume && src_as->volume->type == AFSVL_BACKVOL &&
+		    ctx->type == AFSVL_BACKVOL)
+			return -ENODEV;
+	}
+
+	return 0;
+}
+
+/*
+ * create a vfsmount to be automounted
+ */
+static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
+{
+	struct fs_context *fc;
+	struct vfsmount *mnt;
+	int ret;
+
+	BUG_ON(!d_inode(mntpt));
+
+	fc = fs_context_for_submount(&afs_fs_type, mntpt);
+	if (IS_ERR(fc))
+		return ERR_CAST(fc);
+
+	ret = afs_mntpt_set_params(fc, mntpt);
+	if (!ret)
+		mnt = fc_mount(fc);
+	else
+		mnt = ERR_PTR(ret);
+
+	put_fs_context(fc);
+	return mnt;
+}
+
+/*
+ * handle an automount point
+ */
+struct vfsmount *afs_d_automount(struct path *path)
+{
+	struct vfsmount *newmnt;
+
+	_enter("{%pd}", path->dentry);
+
+	newmnt = afs_mntpt_do_automount(path->dentry);
+	if (IS_ERR(newmnt))
+		return newmnt;
+
+	mnt_set_expiry(newmnt, &afs_vfsmounts);
+	queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
+			   afs_mntpt_expiry_timeout * HZ);
+	_leave(" = %p", newmnt);
+	return newmnt;
+}
+
+/*
+ * handle mountpoint expiry timer going off
+ */
+static void afs_mntpt_expiry_timed_out(struct work_struct *work)
+{
+	_enter("");
+
+	if (!list_empty(&afs_vfsmounts)) {
+		mark_mounts_for_expiry(&afs_vfsmounts);
+		queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
+				   afs_mntpt_expiry_timeout * HZ);
+	}
+
+	_leave("");
+}
+
+/*
+ * kill the AFS mountpoint timer if it's still running
+ */
+void afs_mntpt_kill_timer(void)
+{
+	_enter("");
+
+	ASSERT(list_empty(&afs_vfsmounts));
+	cancel_delayed_work_sync(&afs_mntpt_expiry_timer);
+}