Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[<Conor.Dooley@microchip.com>]

On 09/09/2022 22:27, Andrew Bresticker wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
> PROT_READ with the justification that a write-only PTE is considered a
> reserved PTE permission bit pattern in the privileged spec. This check
> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
> inconsistent with other architectures that don't support write-only PTEs,
> creating a potential software portability issue. Just remove the check
> altogether and let PROT_WRITE imply PROT_READ as is the case on other
> architectures.
> 
> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
> disallowed prior to the aforementioned commit; PROT_READ is implied in
> such mappings as well.
> 
> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")

For the naive members of the audience such as myself, this patch
came after a non-fixes patch in the series. What is the dependence
of this patch on the other one (if any)?
Thanks,
Conor.

> Reviewed-by: Atish Patra <atishp@rivosinc.com>
> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> ---
> v1 -> v2: Update access_error() to account for write-implies-read
> v2 -> v3: Separate into two commits
> ---
>  arch/riscv/kernel/sys_riscv.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 571556bb9261..5d3f2fbeb33c 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>                 return -EINVAL;
> 
> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> -               return -EINVAL;
> -
>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>                                offset >> (PAGE_SHIFT - page_shift_offset));
>  }
> --
> 2.25.1
> 
> 
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