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charset="utf-8" When Xiongchuan Tan tries to run one 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]: modified in commit e0d17c842c0f824fd4df9f4688709fc6907201e1 (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co= mmit/?id=3De0d17c842c0f824fd4df9f4688709fc6907201e1) Reported-by: Xiongchuan Tan Co-developed-by: Wang Ruikang Signed-off-by: Wang Ruikang Co-developed-by: Ruizhe Pan Signed-off-by: Ruizhe Pan Signed-off-by: Celeste Liu Reviewed-by: Guo Ren Cc: linux-riscv@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: Guo Ren Cc: Yash Shah --- v2: This version adds a link to the referenced spec, and reference of the=20 previous related modification. v3: fix DCO signoff name and add comment for reason 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..e55281b497cf 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; =20 - if ((prot & PROT_WRITE) && (prot & PROT_EXEC)) - if (unlikely(!(prot & PROT_READ))) - return -EINVAL; + /* + * As mentioned in Table 4.5 in RISC-V spec Volume 2 Section 4.3 version + * "20211203 Privileged Architecture v1.12, Ratified", 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; =20 return ksys_mmap_pgoff(addr, len, prot, flags, fd, offset >> (PAGE_SHIFT - page_shift_offset)); --=20 2.36.1