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

[Conor Dooley]

Hey Hsieh-Tseng,

On Tue, Apr 25, 2023 at 11:44:07AM +0800, Woodrow Shen wrote:
> 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")

This fixes tag should be:
Fixes: 8aeb7b17f04e ("RISC-V: Make mmap() with PROT_WRITE imply PROT_READ")
as checkpatch would have told you :/ Perhaps Palmer can fix that up on
application?

> Signed-off-by: Hsieh-Tseng Shen <woodrow.shen at sifive.com>
> Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
> ---

This is not v1, it's v2 right?
Please include a changelog between versions.

Also, what makes it an RFC, it's an actual fix that you would like
merged, right?

Thanks,
Conor.

>  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
> 
> 
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