Messages in this thread Patch in this message | | | From | Celeste Liu <> | Subject | [PATCH v4] riscv: don't allow write but not read page mapping request in mmap | Date | Fri, 24 Jun 2022 18:14:28 +0800 |
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When Xiongchuan Tan tries to run oe of libaio's tests[1], it encounters a strange behavior: for the same PROT_WRITE only mapping, there was a discrepancy in whether it could be read before and after writing (readable before writing, unreadable after writing). After some investigation, I found that mmap allows write only mapping, an undefined behavior, on RISC-V.
As mentioned in Table 4.5 in RISC-V spec Volume 2 Section 4.3 version "20211203 Privileged Architecture v1.12, Ratified"[2], the PTE permission bit combination of "write+!read" is "Reserved for future use.". Hence, don't allow such mapping request in mmap call. In the current code[3], write+exec only is marked as invalid, but write only is not marked as invalid.
This patch refines that judgment.
[1]: https://pagure.io/libaio/blob/1b18bfafc6a2f7b9fa2c6be77a95afed8b7be448/f/harness/cases/5.t [2]: https://github.com/riscv/riscv-isa-manual/releases/download/Priv-v1.12/riscv-privileged-20211203.pdf [3]: commit e0d17c842c0f ("RISC-V: Don't allow write+exec only page mapping request in mmap")
Reported-by: Xiongchuan Tan <xc-tan@outlook.com> Co-developed-by: Wang Ruikang <dramforever@live.com> Signed-off-by: Wang Ruikang <dramforever@live.com> Co-developed-by: Ruizhe Pan <c141028@gmail.com> Signed-off-by: Ruizhe Pan <c141028@gmail.com> Signed-off-by: Celeste Liu <coelacanthus@outlook.com> Reviewed-by: Guo Ren <guoren@kernel.org> Cc: linux-riscv@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: Guo Ren <guoren@kernel.org> Cc: Yash Shah <yash.shah@sifive.com> --- v2: This version adds a link to the referenced spec, and reference of the previous related modification. v3: fix DCO signoff name and add comment for reason v4: fix typo in changelog and comment
arch/riscv/kernel/sys_riscv.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c index 9c0194f176fc..f29456cfe68a 100644 --- a/arch/riscv/kernel/sys_riscv.c +++ b/arch/riscv/kernel/sys_riscv.c @@ -18,9 +18,14 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len, if (unlikely(offset & (~PAGE_MASK >> page_shift_offset))) return -EINVAL; - if ((prot & PROT_WRITE) && (prot & PROT_EXEC)) - if (unlikely(!(prot & PROT_READ))) - return -EINVAL; + /* + * As mentioned in Table 4.5 in RISC-V spec (20211203) Volume 2 + * Section 4.3 the PTE permission bit combination of "write+!read" + * is "Reserved for future use.". Hence, don't allow such mapping + * request in mmap call. + */ + 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)); -- 2.36.1
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