[PATCH] riscv: mmap with PROT_WRITE but no PROT_READ is invalid

[Conor Dooley]

Hey Eva,

On Thu, Oct 06, 2022 at 10:20:02PM +0300, Eva Kotova wrote:
> On Tue, 31 May 2022 00:56:52 PDT (-0700), coelacanthus at outlook.com wrote:
> > As mentioned in Table 4.5 in RISC-V spec Volume 2 Section 4.3, write
> > but not read is "Reserved for future use.". For now, they are not valid.
> > In the current code, -wx is marked as invalid, but -w- is not marked
> > as invalid.
> 
> This patch breaks OpenJDK/Java on RISC-V, as it tries to create a w-only
> protective page:
> 
> #
> # There is insufficient memory for the Java Runtime Environment to continue.
> # Native memory allocation (mmap) failed to map 4096 bytes for failed to
> allocate memory for PaX check.
> # An error report file with more information is saved as:
> # /root/hs_err_pid107.log
> 
> I bisected to this commit since on Linux 5.19+ java no longer works.
> Perhaps some fallback should be implemented, to prevent userspace breakage.
> It is currently documented, that at least on i386 PROT_WRITE mappings imply
> PROT_READ (See man mmap(2) NOTES), this would be a good place to start.

Do these patches solve your problem by any chance?
https://lore.kernel.org/linux-riscv/20220915193702.2201018-1-abrestic@rivosinc.com/

I don't know the "area" at all, so it's a shot in the dark, but these
both have Fixes: tags for the patch that you are blaming.

Thanks,
Conor.