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, 363 insertions, 0 deletions

diff --git a/fs/afs/xattr.c b/fs/afs/xattr.c
new file mode 100644
index 000000000..3770ed236
--- /dev/null
+++ b/fs/afs/xattr.c
@@ -0,0 +1,363 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Extended attribute handling for AFS.  We use xattrs to get and set metadata
+ * instead of providing pioctl().
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/xattr.h>
+#include "internal.h"
+
+/*
+ * Deal with the result of a successful fetch ACL operation.
+ */
+static void afs_acl_success(struct afs_operation *op)
+{
+	afs_vnode_commit_status(op, &op->file[0]);
+}
+
+static void afs_acl_put(struct afs_operation *op)
+{
+	kfree(op->acl);
+}
+
+static const struct afs_operation_ops afs_fetch_acl_operation = {
+	.issue_afs_rpc	= afs_fs_fetch_acl,
+	.success	= afs_acl_success,
+	.put		= afs_acl_put,
+};
+
+/*
+ * Get a file's ACL.
+ */
+static int afs_xattr_get_acl(const struct xattr_handler *handler,
+			     struct dentry *dentry,
+			     struct inode *inode, const char *name,
+			     void *buffer, size_t size)
+{
+	struct afs_operation *op;
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct afs_acl *acl = NULL;
+	int ret;
+
+	op = afs_alloc_operation(NULL, vnode->volume);
+	if (IS_ERR(op))
+		return -ENOMEM;
+
+	afs_op_set_vnode(op, 0, vnode);
+	op->ops = &afs_fetch_acl_operation;
+
+	afs_begin_vnode_operation(op);
+	afs_wait_for_operation(op);
+	acl = op->acl;
+	op->acl = NULL;
+	ret = afs_put_operation(op);
+
+	if (ret == 0) {
+		ret = acl->size;
+		if (size > 0) {
+			if (acl->size <= size)
+				memcpy(buffer, acl->data, acl->size);
+			else
+				ret = -ERANGE;
+		}
+	}
+
+	kfree(acl);
+	return ret;
+}
+
+static bool afs_make_acl(struct afs_operation *op,
+			 const void *buffer, size_t size)
+{
+	struct afs_acl *acl;
+
+	acl = kmalloc_flex(*acl, data, size);
+	if (!acl) {
+		afs_op_nomem(op);
+		return false;
+	}
+
+	acl->size = size;
+	memcpy(acl->data, buffer, size);
+	op->acl = acl;
+	return true;
+}
+
+static const struct afs_operation_ops afs_store_acl_operation = {
+	.issue_afs_rpc	= afs_fs_store_acl,
+	.success	= afs_acl_success,
+	.put		= afs_acl_put,
+};
+
+/*
+ * Set a file's AFS3 ACL.
+ */
+static int afs_xattr_set_acl(const struct xattr_handler *handler,
+			     struct mnt_idmap *idmap,
+                             struct dentry *dentry,
+                             struct inode *inode, const char *name,
+                             const void *buffer, size_t size, int flags)
+{
+	struct afs_operation *op;
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+
+	if (flags == XATTR_CREATE)
+		return -EINVAL;
+
+	op = afs_alloc_operation(NULL, vnode->volume);
+	if (IS_ERR(op))
+		return -ENOMEM;
+
+	afs_op_set_vnode(op, 0, vnode);
+	if (!afs_make_acl(op, buffer, size))
+		return afs_put_operation(op);
+
+	op->ops = &afs_store_acl_operation;
+	return afs_do_sync_operation(op);
+}
+
+static const struct xattr_handler afs_xattr_afs_acl_handler = {
+	.name   = "afs.acl",
+	.get    = afs_xattr_get_acl,
+	.set    = afs_xattr_set_acl,
+};
+
+static const struct afs_operation_ops yfs_fetch_opaque_acl_operation = {
+	.issue_yfs_rpc	= yfs_fs_fetch_opaque_acl,
+	.success	= afs_acl_success,
+	/* Don't free op->yacl in .put here */
+};
+
+/*
+ * Get a file's YFS ACL.
+ */
+static int afs_xattr_get_yfs(const struct xattr_handler *handler,
+			     struct dentry *dentry,
+			     struct inode *inode, const char *name,
+			     void *buffer, size_t size)
+{
+	struct afs_operation *op;
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct yfs_acl *yacl = NULL;
+	char buf[16], *data;
+	int which = 0, dsize, ret = -ENOMEM;
+
+	if (strcmp(name, "acl") == 0)
+		which = 0;
+	else if (strcmp(name, "acl_inherited") == 0)
+		which = 1;
+	else if (strcmp(name, "acl_num_cleaned") == 0)
+		which = 2;
+	else if (strcmp(name, "vol_acl") == 0)
+		which = 3;
+	else
+		return -EOPNOTSUPP;
+
+	yacl = kzalloc_obj(struct yfs_acl);
+	if (!yacl)
+		goto error;
+
+	if (which == 0)
+		yacl->flags |= YFS_ACL_WANT_ACL;
+	else if (which == 3)
+		yacl->flags |= YFS_ACL_WANT_VOL_ACL;
+
+	op = afs_alloc_operation(NULL, vnode->volume);
+	if (IS_ERR(op))
+		goto error_yacl;
+
+	afs_op_set_vnode(op, 0, vnode);
+	op->yacl = yacl;
+	op->ops = &yfs_fetch_opaque_acl_operation;
+
+	afs_begin_vnode_operation(op);
+	afs_wait_for_operation(op);
+	ret = afs_put_operation(op);
+
+	if (ret == 0) {
+		switch (which) {
+		case 0:
+			data = yacl->acl->data;
+			dsize = yacl->acl->size;
+			break;
+		case 1:
+			data = buf;
+			dsize = scnprintf(buf, sizeof(buf), "%u", yacl->inherit_flag);
+			break;
+		case 2:
+			data = buf;
+			dsize = scnprintf(buf, sizeof(buf), "%u", yacl->num_cleaned);
+			break;
+		case 3:
+			data = yacl->vol_acl->data;
+			dsize = yacl->vol_acl->size;
+			break;
+		default:
+			ret = -EOPNOTSUPP;
+			goto error_yacl;
+		}
+
+		ret = dsize;
+		if (size > 0) {
+			if (dsize <= size)
+				memcpy(buffer, data, dsize);
+			else
+				ret = -ERANGE;
+		}
+	} else if (ret == -ENOTSUPP) {
+		ret = -ENODATA;
+	}
+
+error_yacl:
+	yfs_free_opaque_acl(yacl);
+error:
+	return ret;
+}
+
+static const struct afs_operation_ops yfs_store_opaque_acl2_operation = {
+	.issue_yfs_rpc	= yfs_fs_store_opaque_acl2,
+	.success	= afs_acl_success,
+	.put		= afs_acl_put,
+};
+
+/*
+ * Set a file's YFS ACL.
+ */
+static int afs_xattr_set_yfs(const struct xattr_handler *handler,
+			     struct mnt_idmap *idmap,
+                             struct dentry *dentry,
+                             struct inode *inode, const char *name,
+                             const void *buffer, size_t size, int flags)
+{
+	struct afs_operation *op;
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	int ret;
+
+	if (flags == XATTR_CREATE ||
+	    strcmp(name, "acl") != 0)
+		return -EINVAL;
+
+	op = afs_alloc_operation(NULL, vnode->volume);
+	if (IS_ERR(op))
+		return -ENOMEM;
+
+	afs_op_set_vnode(op, 0, vnode);
+	if (!afs_make_acl(op, buffer, size))
+		return afs_put_operation(op);
+
+	op->ops = &yfs_store_opaque_acl2_operation;
+	ret = afs_do_sync_operation(op);
+	if (ret == -ENOTSUPP)
+		ret = -ENODATA;
+	return ret;
+}
+
+static const struct xattr_handler afs_xattr_yfs_handler = {
+	.prefix	= "afs.yfs.",
+	.get	= afs_xattr_get_yfs,
+	.set	= afs_xattr_set_yfs,
+};
+
+/*
+ * Get the name of the cell on which a file resides.
+ */
+static int afs_xattr_get_cell(const struct xattr_handler *handler,
+			      struct dentry *dentry,
+			      struct inode *inode, const char *name,
+			      void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct afs_cell *cell = vnode->volume->cell;
+	size_t namelen;
+
+	namelen = cell->name_len;
+	if (size == 0)
+		return namelen;
+	if (namelen > size)
+		return -ERANGE;
+	memcpy(buffer, cell->name, namelen);
+	return namelen;
+}
+
+static const struct xattr_handler afs_xattr_afs_cell_handler = {
+	.name	= "afs.cell",
+	.get	= afs_xattr_get_cell,
+};
+
+/*
+ * Get the volume ID, vnode ID and vnode uniquifier of a file as a sequence of
+ * hex numbers separated by colons.
+ */
+static int afs_xattr_get_fid(const struct xattr_handler *handler,
+			     struct dentry *dentry,
+			     struct inode *inode, const char *name,
+			     void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	char text[16 + 1 + 24 + 1 + 8 + 1];
+	size_t len;
+
+	/* The volume ID is 64-bit, the vnode ID is 96-bit and the
+	 * uniquifier is 32-bit.
+	 */
+	len = scnprintf(text, sizeof(text), "%llx:", vnode->fid.vid);
+	if (vnode->fid.vnode_hi)
+		len += scnprintf(text + len, sizeof(text) - len, "%x%016llx",
+				vnode->fid.vnode_hi, vnode->fid.vnode);
+	else
+		len += scnprintf(text + len, sizeof(text) - len, "%llx",
+				 vnode->fid.vnode);
+	len += scnprintf(text + len, sizeof(text) - len, ":%x",
+			 vnode->fid.unique);
+
+	if (size == 0)
+		return len;
+	if (len > size)
+		return -ERANGE;
+	memcpy(buffer, text, len);
+	return len;
+}
+
+static const struct xattr_handler afs_xattr_afs_fid_handler = {
+	.name	= "afs.fid",
+	.get	= afs_xattr_get_fid,
+};
+
+/*
+ * Get the name of the volume on which a file resides.
+ */
+static int afs_xattr_get_volume(const struct xattr_handler *handler,
+			      struct dentry *dentry,
+			      struct inode *inode, const char *name,
+			      void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	const char *volname = vnode->volume->name;
+	size_t namelen;
+
+	namelen = strlen(volname);
+	if (size == 0)
+		return namelen;
+	if (namelen > size)
+		return -ERANGE;
+	memcpy(buffer, volname, namelen);
+	return namelen;
+}
+
+static const struct xattr_handler afs_xattr_afs_volume_handler = {
+	.name	= "afs.volume",
+	.get	= afs_xattr_get_volume,
+};
+
+const struct xattr_handler * const afs_xattr_handlers[] = {
+	&afs_xattr_afs_acl_handler,
+	&afs_xattr_afs_cell_handler,
+	&afs_xattr_afs_fid_handler,
+	&afs_xattr_afs_volume_handler,
+	&afs_xattr_yfs_handler,		/* afs.yfs. prefix */
+	NULL
+};