linux-kernel - [PATCH v4 1/2] riscv: Make VM_WRITE imply VM

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Date:   Thu, 15 Sep 2022 15:37:01 -0400
From:   Andrew Bresticker <abrestic@...osinc.com>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Celeste Liu <coelacanthus@...look.com>,
        dram <dramforever@...e.com>, Ruizhe Pan <c141028@...il.com>,
        Conor.Dooley@...rochip.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Andrew Bresticker <abrestic@...osinc.com>,
        stable@...r.kernel.org, Atish Patra <atishp@...osinc.com>
Subject: [PATCH v4 1/2] riscv: Make VM_WRITE imply VM_READ

RISC-V does not presently have write-only mappings as that PTE bit pattern
is considered reserved in the privileged spec, so allow handling of read
faults in VMAs that have VM_WRITE without VM_READ in order to be consistent
with other architectures that have similar limitations.

Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
Cc: <stable@...r.kernel.org> # v4.19+
Reviewed-by: Atish Patra <atishp@...osinc.com>
Signed-off-by: Andrew Bresticker <abrestic@...osinc.com>
---
new in v3
v3 -> v4: add Fixes tag
---
 arch/riscv/mm/fault.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index f2fbd1400b7c..d86f7cebd4a7 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -184,7 +184,8 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
 		}
 		break;
 	case EXC_LOAD_PAGE_FAULT:
-		if (!(vma->vm_flags & VM_READ)) {
+		/* Write implies read */
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE))) {
 			return true;
 		}
 		break;
-- 
2.25.1