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, 573 insertions, 0 deletions

diff --git a/fs/readdir.c b/fs/readdir.c
new file mode 100644
index 000000000..76bb1ae3a
--- /dev/null
+++ b/fs/readdir.c
@@ -0,0 +1,573 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/readdir.c
+ *
+ *  Copyright (C) 1995  Linus Torvalds
+ */
+
+#include <linux/stddef.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/time.h>
+#include <linux/mm.h>
+#include <linux/errno.h>
+#include <linux/stat.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/dirent.h>
+#include <linux/security.h>
+#include <linux/syscalls.h>
+#include <linux/unistd.h>
+#include <linux/compat.h>
+#include <linux/uaccess.h>
+
+#define dirent_size(dirent, len) offsetof(typeof(*(dirent)), d_name[len])
+
+/*
+ * Some filesystems were never converted to '->iterate_shared()'
+ * and their directory iterators want the inode lock held for
+ * writing. This wrapper allows for converting from the shared
+ * semantics to the exclusive inode use.
+ */
+int wrap_directory_iterator(struct file *file,
+			    struct dir_context *ctx,
+			    int (*iter)(struct file *, struct dir_context *))
+{
+	struct inode *inode = file_inode(file);
+	int ret;
+
+	/*
+	 * We'd love to have an 'inode_upgrade_trylock()' operation,
+	 * see the comment in mmap_upgrade_trylock() in mm/memory.c.
+	 *
+	 * But considering this is for "filesystems that never got
+	 * converted", it really doesn't matter.
+	 *
+	 * Also note that since we have to return with the lock held
+	 * for reading, we can't use the "killable()" locking here,
+	 * since we do need to get the lock even if we're dying.
+	 *
+	 * We could do the write part killably and then get the read
+	 * lock unconditionally if it mattered, but see above on why
+	 * this does the very simplistic conversion.
+	 */
+	up_read(&inode->i_rwsem);
+	down_write(&inode->i_rwsem);
+
+	/*
+	 * Since we dropped the inode lock, we should do the
+	 * DEADDIR test again. See 'iterate_dir()' below.
+	 *
+	 * Note that we don't need to re-do the f_pos games,
+	 * since the file must be locked wrt f_pos anyway.
+	 */
+	ret = -ENOENT;
+	if (!IS_DEADDIR(inode))
+		ret = iter(file, ctx);
+
+	downgrade_write(&inode->i_rwsem);
+	return ret;
+}
+EXPORT_SYMBOL(wrap_directory_iterator);
+
+/*
+ * Note the "unsafe_put_user()" semantics: we goto a
+ * label for errors.
+ */
+#define unsafe_copy_dirent_name(_dst, _src, _len, label) do {	\
+	char __user *dst = (_dst);				\
+	const char *src = (_src);				\
+	size_t len = (_len);					\
+	unsafe_put_user(0, dst+len, label);			\
+	unsafe_copy_to_user(dst, src, len, label);		\
+} while (0)
+
+
+int iterate_dir(struct file *file, struct dir_context *ctx)
+{
+	struct inode *inode = file_inode(file);
+	int res = -ENOTDIR;
+
+	if (!file->f_op->iterate_shared)
+		goto out;
+
+	res = security_file_permission(file, MAY_READ);
+	if (res)
+		goto out;
+
+	res = fsnotify_file_perm(file, MAY_READ);
+	if (res)
+		goto out;
+
+	res = down_read_killable(&inode->i_rwsem);
+	if (res)
+		goto out;
+
+	res = -ENOENT;
+	if (!IS_DEADDIR(inode)) {
+		ctx->pos = file->f_pos;
+		res = file->f_op->iterate_shared(file, ctx);
+		file->f_pos = ctx->pos;
+		fsnotify_access(file);
+		file_accessed(file);
+	}
+	inode_unlock_shared(inode);
+out:
+	return res;
+}
+EXPORT_SYMBOL(iterate_dir);
+
+/*
+ * POSIX says that a dirent name cannot contain NULL or a '/'.
+ *
+ * It's not 100% clear what we should really do in this case.
+ * The filesystem is clearly corrupted, but returning a hard
+ * error means that you now don't see any of the other names
+ * either, so that isn't a perfect alternative.
+ *
+ * And if you return an error, what error do you use? Several
+ * filesystems seem to have decided on EUCLEAN being the error
+ * code for EFSCORRUPTED, and that may be the error to use. Or
+ * just EIO, which is perhaps more obvious to users.
+ *
+ * In order to see the other file names in the directory, the
+ * caller might want to make this a "soft" error: skip the
+ * entry, and return the error at the end instead.
+ *
+ * Note that this should likely do a "memchr(name, 0, len)"
+ * check too, since that would be filesystem corruption as
+ * well. However, that case can't actually confuse user space,
+ * which has to do a strlen() on the name anyway to find the
+ * filename length, and the above "soft error" worry means
+ * that it's probably better left alone until we have that
+ * issue clarified.
+ *
+ * Note the PATH_MAX check - it's arbitrary but the real
+ * kernel limit on a possible path component, not NAME_MAX,
+ * which is the technical standard limit.
+ */
+static int verify_dirent_name(const char *name, int len)
+{
+	if (len <= 0 || len >= PATH_MAX)
+		return -EIO;
+	if (memchr(name, '/', len))
+		return -EIO;
+	return 0;
+}
+
+/*
+ * Traditional linux readdir() handling..
+ *
+ * "count=1" is a special case, meaning that the buffer is one
+ * dirent-structure in size and that the code can't handle more
+ * anyway. Thus the special "fillonedir()" function for that
+ * case (the low-level handlers don't need to care about this).
+ */
+
+#ifdef __ARCH_WANT_OLD_READDIR
+
+struct old_linux_dirent {
+	unsigned long	d_ino;
+	unsigned long	d_offset;
+	unsigned short	d_namlen;
+	char		d_name[];
+};
+
+struct readdir_callback {
+	struct dir_context ctx;
+	struct old_linux_dirent __user * dirent;
+	int result;
+};
+
+static bool fillonedir(struct dir_context *ctx, const char *name, int namlen,
+		      loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct readdir_callback *buf =
+		container_of(ctx, struct readdir_callback, ctx);
+	struct old_linux_dirent __user * dirent;
+	unsigned long d_ino;
+
+	if (buf->result)
+		return false;
+	buf->result = verify_dirent_name(name, namlen);
+	if (buf->result)
+		return false;
+	d_ino = ino;
+	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
+		buf->result = -EOVERFLOW;
+		return false;
+	}
+	buf->result++;
+	dirent = buf->dirent;
+	scoped_user_write_access_size(dirent, dirent_size(dirent, namlen + 1), efault) {
+		unsafe_put_user(d_ino, &dirent->d_ino, efault);
+		unsafe_put_user(offset, &dirent->d_offset, efault);
+		unsafe_put_user(namlen, &dirent->d_namlen, efault);
+		unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault);
+	}
+	return true;
+efault:
+	buf->result = -EFAULT;
+	return false;
+}
+
+SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
+		struct old_linux_dirent __user *, dirent, unsigned int, count)
+{
+	int error;
+	CLASS(fd_pos, f)(fd);
+	struct readdir_callback buf = {
+		.ctx.actor = fillonedir,
+		.ctx.count = 1, /* Hint to fs: just one entry. */
+		.dirent = dirent
+	};
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	error = iterate_dir(fd_file(f), &buf.ctx);
+	if (buf.result)
+		error = buf.result;
+
+	return error;
+}
+
+#endif /* __ARCH_WANT_OLD_READDIR */
+
+/*
+ * New, all-improved, singing, dancing, iBCS2-compliant getdents()
+ * interface. 
+ */
+struct linux_dirent {
+	unsigned long	d_ino;
+	unsigned long	d_off;
+	unsigned short	d_reclen;
+	char		d_name[];
+};
+
+struct getdents_callback {
+	struct dir_context ctx;
+	struct linux_dirent __user * current_dir;
+	int prev_reclen;
+	int error;
+};
+
+static bool filldir(struct dir_context *ctx, const char *name, int namlen,
+		   loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct linux_dirent __user *dirent, *prev;
+	struct getdents_callback *buf =
+		container_of(ctx, struct getdents_callback, ctx);
+	unsigned long d_ino;
+	int reclen = ALIGN(dirent_size(dirent, namlen + 2), sizeof(long));
+	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
+
+	buf->error = verify_dirent_name(name, namlen);
+	if (unlikely(buf->error))
+		return false;
+	buf->error = -EINVAL;	/* only used if we fail.. */
+	if (reclen > ctx->count)
+		return false;
+	d_ino = ino;
+	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
+		buf->error = -EOVERFLOW;
+		return false;
+	}
+	prev_reclen = buf->prev_reclen;
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
+		return false;
+	dirent = buf->current_dir;
+	prev = (void __user *) dirent - prev_reclen;
+	scoped_user_write_access_size(prev, reclen + prev_reclen, efault) {
+		/* This might be 'dirent->d_off', but if so it will get overwritten */
+		unsafe_put_user(offset, &prev->d_off, efault);
+		unsafe_put_user(d_ino, &dirent->d_ino, efault);
+		unsafe_put_user(reclen, &dirent->d_reclen, efault);
+		unsafe_put_user(d_type, (char __user *)dirent + reclen - 1, efault);
+		unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault);
+	}
+
+	buf->current_dir = (void __user *)dirent + reclen;
+	buf->prev_reclen = reclen;
+	ctx->count -= reclen;
+	return true;
+efault:
+	buf->error = -EFAULT;
+	return false;
+}
+
+SYSCALL_DEFINE3(getdents, unsigned int, fd,
+		struct linux_dirent __user *, dirent, unsigned int, count)
+{
+	CLASS(fd_pos, f)(fd);
+	struct getdents_callback buf = {
+		.ctx.actor = filldir,
+		.ctx.count = count,
+		.ctx.dt_flags_mask = FILLDIR_FLAG_NOINTR,
+		.current_dir = dirent
+	};
+	int error;
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	error = iterate_dir(fd_file(f), &buf.ctx);
+	if (error >= 0)
+		error = buf.error;
+	if (buf.prev_reclen) {
+		struct linux_dirent __user * lastdirent;
+		lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
+
+		if (put_user(buf.ctx.pos, &lastdirent->d_off))
+			error = -EFAULT;
+		else
+			error = count - buf.ctx.count;
+	}
+	return error;
+}
+
+struct getdents_callback64 {
+	struct dir_context ctx;
+	struct linux_dirent64 __user * current_dir;
+	int prev_reclen;
+	int error;
+};
+
+static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
+		     loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct linux_dirent64 __user *dirent, *prev;
+	struct getdents_callback64 *buf =
+		container_of(ctx, struct getdents_callback64, ctx);
+	int reclen = ALIGN(dirent_size(dirent, namlen + 1), sizeof(u64));
+	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
+
+	buf->error = verify_dirent_name(name, namlen);
+	if (unlikely(buf->error))
+		return false;
+	buf->error = -EINVAL;	/* only used if we fail.. */
+	if (reclen > ctx->count)
+		return false;
+	prev_reclen = buf->prev_reclen;
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
+		return false;
+	dirent = buf->current_dir;
+	prev = (void __user *)dirent - prev_reclen;
+	scoped_user_write_access_size(prev, reclen + prev_reclen, efault) {
+		/* This might be 'dirent->d_off', but if so it will get overwritten */
+		unsafe_put_user(offset, &prev->d_off, efault);
+		unsafe_put_user(ino, &dirent->d_ino, efault);
+		unsafe_put_user(reclen, &dirent->d_reclen, efault);
+		unsafe_put_user(d_type, &dirent->d_type, efault);
+		unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault);
+	}
+
+	buf->prev_reclen = reclen;
+	buf->current_dir = (void __user *)dirent + reclen;
+	ctx->count -= reclen;
+	return true;
+
+efault:
+	buf->error = -EFAULT;
+	return false;
+}
+
+SYSCALL_DEFINE3(getdents64, unsigned int, fd,
+		struct linux_dirent64 __user *, dirent, unsigned int, count)
+{
+	CLASS(fd_pos, f)(fd);
+	struct getdents_callback64 buf = {
+		.ctx.actor = filldir64,
+		.ctx.count = count,
+		.ctx.dt_flags_mask = FILLDIR_FLAG_NOINTR,
+		.current_dir = dirent
+	};
+	int error;
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	error = iterate_dir(fd_file(f), &buf.ctx);
+	if (error >= 0)
+		error = buf.error;
+	if (buf.prev_reclen) {
+		struct linux_dirent64 __user * lastdirent;
+		typeof(lastdirent->d_off) d_off = buf.ctx.pos;
+
+		lastdirent = (void __user *) buf.current_dir - buf.prev_reclen;
+		if (put_user(d_off, &lastdirent->d_off))
+			error = -EFAULT;
+		else
+			error = count - buf.ctx.count;
+	}
+	return error;
+}
+
+#ifdef CONFIG_COMPAT
+struct compat_old_linux_dirent {
+	compat_ulong_t	d_ino;
+	compat_ulong_t	d_offset;
+	unsigned short	d_namlen;
+	char		d_name[];
+};
+
+struct compat_readdir_callback {
+	struct dir_context ctx;
+	struct compat_old_linux_dirent __user *dirent;
+	int result;
+};
+
+static bool compat_fillonedir(struct dir_context *ctx, const char *name,
+			     int namlen, loff_t offset, u64 ino,
+			     unsigned int d_type)
+{
+	struct compat_readdir_callback *buf =
+		container_of(ctx, struct compat_readdir_callback, ctx);
+	struct compat_old_linux_dirent __user *dirent;
+	compat_ulong_t d_ino;
+
+	if (buf->result)
+		return false;
+	buf->result = verify_dirent_name(name, namlen);
+	if (buf->result)
+		return false;
+	d_ino = ino;
+	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
+		buf->result = -EOVERFLOW;
+		return false;
+	}
+	buf->result++;
+	dirent = buf->dirent;
+	scoped_user_write_access_size(dirent, dirent_size(dirent, namlen + 1), efault) {
+		unsafe_put_user(d_ino, &dirent->d_ino, efault);
+		unsafe_put_user(offset, &dirent->d_offset, efault);
+		unsafe_put_user(namlen, &dirent->d_namlen, efault);
+		unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault);
+	}
+	return true;
+efault:
+	buf->result = -EFAULT;
+	return false;
+}
+
+COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
+		struct compat_old_linux_dirent __user *, dirent, unsigned int, count)
+{
+	int error;
+	CLASS(fd_pos, f)(fd);
+	struct compat_readdir_callback buf = {
+		.ctx.actor = compat_fillonedir,
+		.ctx.count = 1, /* Hint to fs: just one entry. */
+		.dirent = dirent
+	};
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	error = iterate_dir(fd_file(f), &buf.ctx);
+	if (buf.result)
+		error = buf.result;
+
+	return error;
+}
+
+struct compat_linux_dirent {
+	compat_ulong_t	d_ino;
+	compat_ulong_t	d_off;
+	unsigned short	d_reclen;
+	char		d_name[];
+};
+
+struct compat_getdents_callback {
+	struct dir_context ctx;
+	struct compat_linux_dirent __user *current_dir;
+	int prev_reclen;
+	int error;
+};
+
+static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen,
+		loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct compat_linux_dirent __user *dirent, *prev;
+	struct compat_getdents_callback *buf =
+		container_of(ctx, struct compat_getdents_callback, ctx);
+	compat_ulong_t d_ino;
+	int reclen = ALIGN(dirent_size(dirent, namlen + 2), sizeof(compat_long_t));
+	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
+
+	buf->error = verify_dirent_name(name, namlen);
+	if (unlikely(buf->error))
+		return false;
+	buf->error = -EINVAL;	/* only used if we fail.. */
+	if (reclen > ctx->count)
+		return false;
+	d_ino = ino;
+	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
+		buf->error = -EOVERFLOW;
+		return false;
+	}
+	prev_reclen = buf->prev_reclen;
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
+		return false;
+	dirent = buf->current_dir;
+	prev = (void __user *) dirent - prev_reclen;
+	scoped_user_write_access_size(prev, reclen + prev_reclen, efault) {
+		unsafe_put_user(offset, &prev->d_off, efault);
+		unsafe_put_user(d_ino, &dirent->d_ino, efault);
+		unsafe_put_user(reclen, &dirent->d_reclen, efault);
+		unsafe_put_user(d_type, (char __user *)dirent + reclen - 1, efault);
+		unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault);
+	}
+
+	buf->prev_reclen = reclen;
+	buf->current_dir = (void __user *)dirent + reclen;
+	ctx->count -= reclen;
+	return true;
+efault:
+	buf->error = -EFAULT;
+	return false;
+}
+
+COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
+		struct compat_linux_dirent __user *, dirent, unsigned int, count)
+{
+	CLASS(fd_pos, f)(fd);
+	struct compat_getdents_callback buf = {
+		.ctx.actor = compat_filldir,
+		.ctx.count = count,
+		.ctx.dt_flags_mask = FILLDIR_FLAG_NOINTR,
+		.current_dir = dirent,
+	};
+	int error;
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	error = iterate_dir(fd_file(f), &buf.ctx);
+	if (error >= 0)
+		error = buf.error;
+	if (buf.prev_reclen) {
+		struct compat_linux_dirent __user * lastdirent;
+		lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;
+
+		if (put_user(buf.ctx.pos, &lastdirent->d_off))
+			error = -EFAULT;
+		else
+			error = count - buf.ctx.count;
+	}
+	return error;
+}
+#endif