linux-kernel - Re: [PATCH v2 3/6] RISC-V: Enforce protections for kernel sections early

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Date:   Tue, 27 Oct 2020 12:00:40 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Atish Patra <atish.patra@....com>
Cc:     linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anup Patel <anup@...infault.org>,
        Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...e.de>,
        Greentime Hu <greentime.hu@...ive.com>,
        Kees Cook <keescook@...omium.org>,
        linux-riscv@...ts.infradead.org,
        Michel Lespinasse <walken@...gle.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Zong Li <zong.li@...ive.com>
Subject: Re: [PATCH v2 3/6] RISC-V: Enforce protections for kernel sections
 early

On Mon, Oct 26, 2020 at 04:02:51PM -0700, Atish Patra wrote:
> Currently, all memblocks are mapped with PAGE_KERNEL_EXEC and the strict
> permissions are only enforced after /init starts. This leaves the kernel
> vulnerable from possible buggy built-in modules.
> 
> Apply permissions to individual sections as early as possible.
> 
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/include/asm/set_memory.h |  2 ++
>  arch/riscv/kernel/setup.c           |  2 ++
>  arch/riscv/mm/init.c                | 11 +++++++++--
>  3 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index 4c5bae7ca01c..4cc3a4e2afd3 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -15,11 +15,13 @@ 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);
> +void protect_kernel_text_data(void);
>  #else
>  static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
>  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) {};
>  #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 7d6a04ae3929..b722c5bf892c 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -22,6 +22,7 @@
>  #include <asm/cpu_ops.h>
>  #include <asm/early_ioremap.h>
>  #include <asm/setup.h>
> +#include <asm/set_memory.h>
>  #include <asm/sections.h>
>  #include <asm/sbi.h>
>  #include <asm/tlbflush.h>
> @@ -92,6 +93,7 @@ void __init setup_arch(char **cmdline_p)
>  #if IS_ENABLED(CONFIG_RISCV_SBI)
>  	sbi_init();
>  #endif
> +	protect_kernel_text_data();
>  #ifdef CONFIG_SWIOTLB
>  	swiotlb_init(1);
>  #endif
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index ea933b789a88..5f196f8158d4 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -608,7 +608,7 @@ static inline void setup_vm_final(void)
>  #endif /* CONFIG_MMU */
>  
>  #ifdef CONFIG_STRICT_KERNEL_RWX
> -void mark_rodata_ro(void)
> +void protect_kernel_text_data(void)
>  {
>  	unsigned long text_start = (unsigned long)_text;
>  	unsigned long text_end = (unsigned long)_etext;
> @@ -617,9 +617,16 @@ void mark_rodata_ro(void)
>  	unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
>  

A comment about that rodata permissions are set later would be nice
here.

>  	set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> -	set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
>  	set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
>  	set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> +}
> +
> +void mark_rodata_ro(void)
> +{
> +	unsigned long rodata_start = (unsigned long)__start_rodata;
> +	unsigned long data_start = (unsigned long)_data;
> +
> +	set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
>  
>  	debug_checkwx();
>  }
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.