Messages in this thread | | | Date | Tue, 11 Oct 2022 18:04:02 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH v4 0/2] Make mmap() with PROT_WRITE imply PROT_READ |
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Hey Palmer,
On Thu, Sep 15, 2022 at 03:37:00PM -0400, Andrew Bresticker wrote: > Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is > invalid") made mmap() reject mappings with only PROT_WRITE set in an > attempt to fix an observed inconsistency in behavior when attempting > to read from a PROT_WRITE-only mapping. The root cause of this behavior > was actually that while RISC-V's protection_map maps VM_WRITE to > readable PTE permissions (since write-only PTEs are considered reserved > by the privileged spec), the page fault handler considered loads from > VM_WRITE-only VMAs illegal accesses. Fix the underlying cause by > handling faults in VM_WRITE-only VMAs (patch 1) and then re-enable > use of mmap(PROT_WRITE) (patch 2), making RISC-V's behavior consistent > with all other architectures that don't support write-only PTEs. > > Both patches are tagged as fixes for the aforementioned commit since that > commit made a userspace visible change that will break any software relying > on mmap(PROT_WRITE). (Also cc: stable since the offending commit was > itself backported to stable).
The patch that these commits fix has hit the distros & manifests as a userspace breakage for openJDK: https://lore.kernel.org/linux-riscv/a69ee775-e565-3d72-eb5f-8378616694d3@gmail.com/ https://lore.kernel.org/linux-riscv/d6c9e249-08bd-4439-7dcc-371b32e7b851@canonical.com/
Eva tested these patches and reported that their problem was fixed: https://lore.kernel.org/linux-riscv/20282242-5cad-42be-ce6c-834b0e7ef269@gmail.com/
I asked them for a T-b but I don't see one on lore etc, but it would be from Eva Kotova <nyandarknessgirl@gmail.com> if you consider their comments their sufficient for a T-B
Thanks, Conor.
> > v1 -> v2: Allow handling of load faults in VM_WRITE VMAs > v2 -> v3: Split into two pathces > v3 -> v4: Fixes tags (+ this cover letter) > > Andrew Bresticker (2): > riscv: Make VM_WRITE imply VM_READ > riscv: Allow PROT_WRITE-only mmap() > > arch/riscv/kernel/sys_riscv.c | 3 --- > arch/riscv/mm/fault.c | 3 ++- > 2 files changed, 2 insertions(+), 4 deletions(-) > > -- > 2.25.1 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv
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