Well, it may be easier to offer an open source RISC-V processor in products, but it's certainly not necessary.
From Wikipedia:
> The RISC-V authors aim to provide several freely available CPU designs, under a BSD license. This license allows derivative works such as RISC-V chip designs to be either open and free like RISC-V itself, or closed and proprietary, (unlike the available OpenRISC cores, which under the GPL, requires that all derivative works also be open and free).
So if it's not GPL, such as OpenRISC, then it's not guaranteed to be fully open source. You could still have 99% of the chip as open source and the other 1% as the proprietary backdoor.
It's not even clear what certain parts of the GPL mean when applied to interpreted languages, like Javascript. Applying the GPL to more exotic languages like HDLs is a legal black hole; I don't think even the FSF is entirely sure how that would play out.
(Which, of course, means that no sane manufacturer would touch GPLed hardware designs.)
From Wikipedia:
> The RISC-V authors aim to provide several freely available CPU designs, under a BSD license. This license allows derivative works such as RISC-V chip designs to be either open and free like RISC-V itself, or closed and proprietary, (unlike the available OpenRISC cores, which under the GPL, requires that all derivative works also be open and free).
https://en.wikipedia.org/wiki/RISC-V
So if it's not GPL, such as OpenRISC, then it's not guaranteed to be fully open source. You could still have 99% of the chip as open source and the other 1% as the proprietary backdoor.