Dave Hansen 684db631a1 uaccess: Add speculation barrier to copy_from_user()
commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47 upstream.

The results of "access_ok()" can be mis-speculated.  The result is that
you can end speculatively:

	if (access_ok(from, size))
		// Right here

even for bad from/size combinations.  On first glance, it would be ideal
to just add a speculation barrier to "access_ok()" so that its results
can never be mis-speculated.

But there are lots of system calls just doing access_ok() via
"copy_to_user()" and friends (example: fstat() and friends).  Those are
generally not problematic because they do not _consume_ data from
userspace other than the pointer.  They are also very quick and common
system calls that should not be needlessly slowed down.

"copy_from_user()" on the other hand uses a user-controller pointer and
is frequently followed up with code that might affect caches.  Take
something like this:

	if (!copy_from_user(&kernelvar, uptr, size))
		do_something_with(kernelvar);

If userspace passes in an evil 'uptr' that *actually* points to a kernel
addresses, and then do_something_with() has cache (or other)
side-effects, it could allow userspace to infer kernel data values.

Add a barrier to the common copy_from_user() code to prevent
mis-speculated values which happen after the copy.

Also add a stub for architectures that do not define barrier_nospec().
This makes the macro usable in generic code.

Since the barrier is now usable in generic code, the x86 #ifdef in the
BPF code can also go away.

Reported-by: Jordy Zomer <jordyzomer@google.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>   # BPF bits
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-02-25 11:25:41 +01:00
..
2022-05-09 17:20:37 -07:00
2021-09-08 11:50:26 -07:00
2021-07-08 11:48:20 -07:00
2021-05-06 19:24:12 -07:00
2022-09-26 12:19:12 -07:00
2018-08-16 12:14:42 -07:00
2021-01-21 14:06:00 -07:00
2022-03-07 12:48:35 -07:00
2021-08-19 09:02:55 +09:00
2022-09-01 18:04:43 +02:00
2022-04-22 21:30:57 +02:00
2021-01-03 20:05:18 -05:00
2022-03-07 12:48:35 -07:00
2022-04-29 14:38:01 -07:00
2022-07-10 13:55:49 -07:00
2022-10-03 14:03:21 -07:00
2021-08-19 09:02:55 +09:00
2021-07-08 11:48:20 -07:00
2021-07-08 11:48:20 -07:00
2018-10-16 13:45:44 +02:00
2021-07-08 11:48:20 -07:00
2022-10-03 17:34:32 -07:00
2021-09-17 13:52:17 +01:00
2021-07-08 11:48:20 -07:00
2021-07-08 11:48:20 -07:00
2021-07-08 11:48:20 -07:00
2022-06-03 10:34:34 -07:00
2021-06-18 11:43:09 +02:00
2021-07-08 11:48:20 -07:00
2022-01-20 08:52:54 +02:00
2018-10-15 16:31:29 -04:00
2022-10-10 11:24:19 -07:00