Re: [PATCH v23 06/28] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE

[Deepak Gupta]

On Sat, May 30, 2026 at 2:47 PM Andreas Schwab <schwab@xxxxxxxxxxxxxx> wrote:
>
> On Mai 30 2026, Deepak Gupta wrote:
>
> > I see two ways forward:
> >
> > - It can be done in generic way where incoming PROT_WRITE means
> >   PROT_READ | PROT_WRITE irrespective of RISC-V. Although others
> >   (x86, arm, etc) would have to weigh in.
> >
> > OR
> >
> > - mmap04 LTP test can be updated to expect either of "rw-p" or "-w-p"
> >   whenever only PROT_WRITE was specified.
>
> OR
>
> - Add a new PROT_ flag.

This was settled when x86 introduced shadow stack. Instead of having
new `PROT_`, it was agreed to create a new syscall for mapping shadow
stack memory (syscall: `map_shadow_stack`). Scenarios like `clone3` or
co-routines required manufacturing a shadow stack, thus necessitating a
new mechanism to create shadow stack style memory in demand. Instead
of having a new PROT_ flag,  a new syscall was created.

>
> --
> Andreas Schwab, schwab@xxxxxxxxxxxxxx
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> "And now for something completely different."