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 <w...@kernel.org>
>> Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
Reviewed-by: Thomas Gleixner <t...@linutronix.de>
