x86/uaccess: Use pointer masking to limit uaccess speculation
The x86 uaccess code uses barrier_nospec() in various places to prevent
speculative dereferencing of user-controlled pointers (which might be
combined with further gadgets or CPU bugs to leak data).
There are some issues with the current implementation:
- The barrier_nospec() in copy_from_user() was inadvertently removed
with: 4b842e4e25b1 ("x86: get rid of small constant size cases in
raw_copy_{to,from}_user()")
- copy_to_user() and friends should also have a speculation barrier,
because a speculative write to a user-controlled address can still
populate the cache line with the original data.
- The LFENCE in barrier_nospec() is overkill, when more lightweight user
pointer masking can be used instead.
Remove all existing barrier_nospec() usage, and instead do user pointer
masking, throughout the x86 uaccess code. This is similar to what arm64
is already doing with uaccess_mask_ptr().
barrier_nospec() is now unused, and can be removed.
Fixes: 4b842e4e25b1 ("x86: get rid of small constant size cases in raw_copy_{to,from}_user()")
Suggested-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
14 files changed
