Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 04 Mar 2020 17:21:57 -0800 (PST)
Subject:     Re: [PATCH 6/8] riscv: add STRICT_KERNEL_RWX support
In-Reply-To: <20200217083223.2011-7-zong.li@sifive.com>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        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-5d8ed200-0200-4198-946f-ae41ba71cc06@palmerdabbelt-glaptop1>
Mime-Version: 1.0 (MHng)
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, 17 Feb 2020 00:32:21 PST (-0800), 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                | 45 +++++++++++++++++++++++++++++
>  3 files changed, 54 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index f524d7e60648..308a4dbc0b39 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -62,6 +62,7 @@ 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 a91f192063c2..d3076087cb34 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -15,6 +15,14 @@ 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);
>
> +#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 965a8cf4829c..09fa643e079c 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -12,11 +12,13 @@
>  #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>
>  #include <asm/sections.h>
>  #include <asm/pgtable.h>
> +#include <asm/ptdump.h>
>  #include <asm/io.h>
>
>  #include "../kernel/head.h"
> @@ -477,6 +479,49 @@ static void __init setup_vm_final(void)
>  	csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
>  	local_flush_tlb_all();
>  }
> +
> +#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)_sdata;
> +	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);

Ya, this'll risk barfing because of srodata.

> +	set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> +}
> +#endif
> +
> +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)
>  {