Re: [PATCH v2 5/6] RISC-V: Protect .init.text & .init.data

[Mike Rapoport <rppt@kernel.org>]

On Mon, Oct 26, 2020 at 04:02:53PM -0700, Atish Patra wrote:
> Currently, .init.text & .init.data are intermixed which makes it impossible
> apply different permissions to them. .init.data shouldn't need exec
> permissions while .init.text shouldn't have write permission.
> 
> Keep them in separate sections so that different permissions are applied to
> each section. This improves the kernel protection under
> CONFIG_STRICT_KERNEL_RWX. We also need to restore the permissions for the
> entire _init section after it is freed so that those pages can be used for
> other purpose.
> 
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
>  arch/riscv/include/asm/sections.h   |  2 ++
>  arch/riscv/include/asm/set_memory.h |  2 ++
>  arch/riscv/kernel/setup.c           |  9 +++++
>  arch/riscv/kernel/vmlinux.lds.S     | 51 ++++++++++++++++-------------
>  arch/riscv/mm/init.c                |  8 ++++-
>  arch/riscv/mm/pageattr.c            |  6 ++++
>  6 files changed, 54 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
> index 3a9971b1210f..1595c5b60cfd 100644
> --- a/arch/riscv/include/asm/sections.h
> +++ b/arch/riscv/include/asm/sections.h
> @@ -9,5 +9,7 @@
>  
>  extern char _start[];
>  extern char _start_kernel[];
> +extern char __init_data_begin[], __init_data_end[];
> +extern char __init_text_begin[], __init_text_end[];
>  
>  #endif /* __ASM_SECTIONS_H */
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index 4cc3a4e2afd3..913429c9c1ae 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -15,6 +15,7 @@ int set_memory_ro(unsigned long addr, int numpages);
>  int set_memory_rw(unsigned long addr, int numpages);
>  int set_memory_x(unsigned long addr, int numpages);
>  int set_memory_nx(unsigned long addr, int numpages);
> +int set_memory_default(unsigned long addr, int numpages);
>  void protect_kernel_text_data(void);
>  #else
>  static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> @@ -22,6 +23,7 @@ static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
>  static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
>  static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
>  static inline void protect_kernel_text_data(void) {};
> +static inline int set_memory_default(unsigned long addr, int numpages) { return 0; }
>  #endif
>  
>  int set_direct_map_invalid_noflush(struct page *page);
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index b722c5bf892c..abfbdc8cfef3 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -123,3 +123,12 @@ static int __init topology_init(void)
>  	return 0;
>  }
>  subsys_initcall(topology_init);
> +
> +void free_initmem(void)
> +{
> +	unsigned long init_begin = (unsigned long)__init_begin;
> +	unsigned long init_end = (unsigned long)__init_end;
> +
> +	set_memory_default(init_begin, (init_end - init_begin) >> PAGE_SHIFT);

And what does "default" imply?
Maybe set_memory_rw() would better name ...

> +	free_initmem_default(POISON_FREE_INITMEM);
> +}

...

> diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> index 19fecb362d81..04f3fc16aa9c 100644
> --- a/arch/riscv/mm/pageattr.c
> +++ b/arch/riscv/mm/pageattr.c
> @@ -128,6 +128,12 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
>  	return ret;
>  }
>  
> +int set_memory_default(unsigned long addr, int numpages)
> +{
> +	return __set_memory(addr, numpages, __pgprot(_PAGE_KERNEL),
> +			    __pgprot(_PAGE_EXEC));

... because you'd need to find what _PAGE_KERNEL is, do bitwise ops and
than find out that default is apparently RW :)

> +}
> +
>  int set_memory_ro(unsigned long addr, int numpages)
>  {
>  	return __set_memory(addr, numpages, __pgprot(_PAGE_READ),
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.