[RFC PATCH] 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 8aeb7b17f04e ("RISC-V: Make mmap() with PROT_WRITE imply PROT_READ")
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_EXEC` and then `PAGE_COPY_READ_EXEC` should be just used instead.
This aligns the other arches (i.e arm64) for protection_map.

Fixes: 8aeb7b17f04e ("RISC-V: Make mmap() with PROT_WRITE imply PROT_READ")
Signed-off-by: Hsieh-Tseng Shen <woodrow.shen at sifive.com>
---
 arch/riscv/include/asm/pgtable.h | 1 -
 arch/riscv/mm/init.c             | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index f641837ccf31..bb1e05367739 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -165,7 +165,6 @@ 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_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..8b8c6ad85fdb 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -285,7 +285,7 @@ static const pgprot_t protection_map[16] = {
 	[VM_WRITE | VM_READ]				= PAGE_COPY,
 	[VM_EXEC]					= PAGE_EXEC,
 	[VM_EXEC | VM_READ]				= PAGE_READ_EXEC,
-	[VM_EXEC | VM_WRITE]				= PAGE_COPY_EXEC,
+	[VM_EXEC | VM_WRITE]				= PAGE_COPY_READ_EXEC,
 	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY_READ_EXEC,
 	[VM_SHARED]					= PAGE_NONE,
 	[VM_SHARED | VM_READ]				= PAGE_READ,
-- 
2.34.1