RISC-V: Make mmap() with PROT_WRITE imply PROT_READ
Commit 2139619b ("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. * remotes/palmer/riscv-wonly: riscv: Allow PROT_WRITE-only mmap() riscv: Make VM_WRITE imply VM_READ Link: https://lore.kernel.org/r/20220915193702.2201018-1-abrestic@rivosinc.com/Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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