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From:   Andrew Bresticker <abrestic@rivosinc.com>
To:     Palmer Dabbelt <palmer@dabbelt.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Atish Patra <atishp@atishpatra.org>,
        Celeste Liu <coelacanthus@outlook.com>,
        dram <dramforever@live.com>, Ruizhe Pan <c141028@gmail.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Andrew Bresticker <abrestic@rivosinc.com>
Subject: [PATCH] riscv: Allow PROT_WRITE-only mmap()
Date:   Thu,  8 Sep 2022 13:01:33 -0400
Message-Id: <20220908170133.1159747-1-abrestic@rivosinc.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
PROT_READ with the justification that a write-only PTE is considered a
reserved PTE permission bit pattern in the privileged spec. This check
is unnecessary since RISC-V defines its protection_map such that PROT_WRITE
maps to the same PTE permissions as PROT_WRITE|PROT_READ, and it is
inconsistent with other architectures that don't support write-only PTEs,
creating a potential software portability issue. Just remove the check
altogether and let PROT_WRITE imply PROT_READ as is the case on other
architectures.

Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
 arch/riscv/kernel/sys_riscv.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 571556bb9261..5d3f2fbeb33c 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
 	if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
 		return -EINVAL;
 
-	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));
 }
-- 
2.25.1