Re: [PATCH] linux-user: mprotect() should returns 0 when len is 0.

[Richard Henderson]

On 10/6/22 11:13, Peter Maydell wrote:
> On Thu, 6 Oct 2022 at 19:05, Soichiro Isshiki
> <sisshiki@isshiki-clinic.com> wrote:
> > From: sisshiki1969 <sisshiki@mac.com>
> >
> > For now, qemu-x86_64 returns ENOMEM when mprotect() was called with an argument
> > len is 0 from a guest process.
> > This behavior is incompatible with the current Linux implementation,
> > which mprotect() with len = 0 does nothing and returns 0,
> > although it does not appear to be explicitly described in man.
> >
> > This is due to the following function which always returns false if len = 0.
> >
> > ```C
> > static inline bool guest_range_valid_untagged(abi_ulong start, abi_ulong len)
> > {
> >      return len - 1 <= GUEST_ADDR_MAX && start <= GUEST_ADDR_MAX - len + 1;
> > }
...
> Cc'ing Richard -- is this the right fix, or would it be better instead
> to make guest_range_valid_untagged() correctly handle a zero-length
> range ?

I think fixing the range check might be best.


r~