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Date:   Fri, 17 Apr 2020 17:30:38 -0700 (PDT)
Subject:     Re: [PATCH v5 9/9] riscv: add STRICT_KERNEL_RWX support
In-Reply-To: <100e739c5fd722a96fcc640c8ee0c82fe34fcb6a.1586332296.git.zong.li@sifive.com>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        mhiramat@kernel.org, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, zong.li@sifive.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     zong.li@sifive.com
Message-ID: <mhng-09f91ec8-5821-41ad-a743-3842ca10f9e2@palmerdabbelt-glaptop1>
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On Wed, 08 Apr 2020 00:57:04 PDT (-0700), zong.li@sifive.com wrote:
> The commit contains that make text section as non-writable, rodata
> section as read-only, and data section as non-executable.
>
> The init section should be changed to non-executable.
>
> Signed-off-by: Zong Li <zong.li@sifive.com>
> ---
>  arch/riscv/Kconfig                  |  1 +
>  arch/riscv/include/asm/set_memory.h |  8 ++++++
>  arch/riscv/mm/init.c                | 44 +++++++++++++++++++++++++++++
>  3 files changed, 53 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 1e1efc998baf..58b556167d59 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -61,6 +61,7 @@ config RISCV
>  	select ARCH_HAS_GIGANTIC_PAGE
>  	select ARCH_HAS_SET_DIRECT_MAP
>  	select ARCH_HAS_SET_MEMORY
> +	select ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
>  	select SPARSEMEM_STATIC if 32BIT
>  	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index 4c5bae7ca01c..c38df4771c09 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -22,6 +22,14 @@ 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; }
>  #endif
>
> +#ifdef CONFIG_STRICT_KERNEL_RWX
> +void set_kernel_text_ro(void);
> +void set_kernel_text_rw(void);
> +#else
> +static inline void set_kernel_text_ro(void) { }
> +static inline void set_kernel_text_rw(void) { }
> +#endif
> +
>  int set_direct_map_invalid_noflush(struct page *page);
>  int set_direct_map_default_noflush(struct page *page);
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fab855963c73..b55be44ff9bd 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -12,6 +12,7 @@
>  #include <linux/sizes.h>
>  #include <linux/of_fdt.h>
>  #include <linux/libfdt.h>
> +#include <linux/set_memory.h>
>
>  #include <asm/fixmap.h>
>  #include <asm/tlbflush.h>
> @@ -477,6 +478,17 @@ static void __init setup_vm_final(void)
>  	csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
>  	local_flush_tlb_all();
>  }
> +
> +void free_initmem(void)
> +{
> +	unsigned long init_begin = (unsigned long)__init_begin;
> +	unsigned long init_end = (unsigned long)__init_end;
> +
> +	/* Make the region as non-execuatble. */
> +	set_memory_nx(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
> +	free_initmem_default(POISON_FREE_INITMEM);
> +}
> +
>  #else
>  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  {
> @@ -488,6 +500,38 @@ static inline void setup_vm_final(void)
>  }
>  #endif /* CONFIG_MMU */
>
> +#ifdef CONFIG_STRICT_KERNEL_RWX
> +void set_kernel_text_rw(void)
> +{
> +	unsigned long text_start = (unsigned long)_text;
> +	unsigned long text_end = (unsigned long)_etext;
> +
> +	set_memory_rw(text_start, (text_end - text_start) >> PAGE_SHIFT);
> +}
> +
> +void set_kernel_text_ro(void)
> +{
> +	unsigned long text_start = (unsigned long)_text;
> +	unsigned long text_end = (unsigned long)_etext;
> +
> +	set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> +}
> +
> +void mark_rodata_ro(void)
> +{
> +	unsigned long text_start = (unsigned long)_text;
> +	unsigned long text_end = (unsigned long)_etext;
> +	unsigned long rodata_start = (unsigned long)__start_rodata;
> +	unsigned long data_start = (unsigned long)_data;
> +	unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> +
> +	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);
> +}
> +#endif
> +
>  void __init paging_init(void)
>  {
>  	setup_vm_final();

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>