Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v3] x86/uaccess: Use pointer masking to limit uaccess speculation | Date | Mon, 14 Sep 2020 22:51:56 +0200 |
| |
On Mon, Sep 14 2020 at 14:53, Josh Poimboeuf wrote: > Al, > > This depends on Christoph's set_fs() removal patches. Would you be > willing to take this in your tree?
Ack.
> On Thu, Sep 10, 2020 at 12:22:53PM -0500, Josh Poimboeuf wrote: >> 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> >> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
| |