[RFC PATCH v1] riscv: mm: Ensure prot of VM_WRITE and VM_EXEC must be readable

[Woodrow Shen]

From: Hsieh-Tseng Shen <woodrow.shen at sifive.com>

The commit 8aeb7b1 allows riscv to use mmap with PROT_WRITE only,
and meanwhile mmap with w+x is also permitted. However, when userspace
tries to access this page with PROT_WRITE|PROT_EXEC, which causes
infinite loop at load page fault as well as it triggers soft lockup.
According to riscv privileged spec, "Writable pages must also be marked
readable". The fix to drop the `PAGE_COPY_READ_EXEC` and `PAGE_READ_EXEC`
should be just used instead. This aligns the other arches (i.e arm64)
for protection_map.

Fixes: 8aeb7b1 ("RISC-V: Make mmap() with PROT_WRITE imply PROT_READ")
Signed-off-by: Hsieh-Tseng Shen <woodrow.shen at sifive.com>
Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
---
 arch/riscv/include/asm/pgtable.h | 3 +--
 arch/riscv/mm/init.c             | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index f641837ccf31..05eda3281ba9 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -165,8 +165,7 @@ extern struct pt_alloc_ops pt_ops __initdata;
 					 _PAGE_EXEC | _PAGE_WRITE)
 
 #define PAGE_COPY		PAGE_READ
-#define PAGE_COPY_EXEC		PAGE_EXEC
-#define PAGE_COPY_READ_EXEC	PAGE_READ_EXEC
+#define PAGE_COPY_EXEC		PAGE_READ_EXEC
 #define PAGE_SHARED		PAGE_WRITE
 #define PAGE_SHARED_EXEC	PAGE_WRITE_EXEC
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 0f14f4a8d179..cc48b0d93a98 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -286,7 +286,7 @@ static const pgprot_t protection_map[16] = {
 	[VM_EXEC]					= PAGE_EXEC,
 	[VM_EXEC | VM_READ]				= PAGE_READ_EXEC,
 	[VM_EXEC | VM_WRITE]				= PAGE_COPY_EXEC,
-	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_READ_EXEC,
+	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_EXEC,
 	[VM_SHARED]					= PAGE_NONE,
 	[VM_SHARED | VM_READ]				= PAGE_READ,
 	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
-- 
2.34.1