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Date:   Fri, 25 Jun 2021 21:30:15 +0800
From:   Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
To:     Alexandre Ghiti <alex@ghiti.fr>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Jisheng Zhang <jszhang@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Zong Li <zong.li@sifive.com>, Anup Patel <anup@brainfault.org>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 2/2] riscv: Map the kernel with correct permissions
 the first time
Message-ID: <20210625213015.12f312e9@xhacker>
In-Reply-To: <20210624120041.2786419-3-alex@ghiti.fr>
References: <20210624120041.2786419-1-alex@ghiti.fr>
        <20210624120041.2786419-3-alex@ghiti.fr>
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On Thu, 24 Jun 2021 14:00:41 +0200
Alexandre Ghiti <alex@ghiti.fr> wrote:

> For 64-bit kernels, we map all the kernel with write and execute
> permissions and afterwards remove writability from text and executability
> from data.
> 
> For 32-bit kernels, the kernel mapping resides in the linear mapping, so we
> map all the linear mapping as writable and executable and afterwards we
> remove those properties for unused memory and kernel mapping as
> described above.
> 
> Change this behavior to directly map the kernel with correct permissions
> and avoid going through the whole mapping to fix the permissions.
> 
> At the same time, this fixes an issue introduced by commit 2bfc6cd81bd1
> ("riscv: Move kernel mapping outside of linear mapping") as reported
> here https://github.com/starfive-tech/linux/issues/17.
> 
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Reviewed-by: Anup Patel <anup@brainfault.org>

Reviewed-by: Jisheng Zhang <jszhang@kernel.org>

> ---
>  arch/riscv/include/asm/page.h       |  13 +++-
>  arch/riscv/include/asm/sections.h   |  17 +++++
>  arch/riscv/include/asm/set_memory.h |   8 --
>  arch/riscv/kernel/setup.c           |  12 +--
>  arch/riscv/mm/init.c                | 112 ++++++++++++----------------
>  5 files changed, 81 insertions(+), 81 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index a1b888f77d57..1c2010c292b3 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -87,6 +87,7 @@ extern unsigned long va_kernel_pa_offset;
>  extern unsigned long va_kernel_xip_pa_offset;
>  #endif
>  extern unsigned long pfn_base;
> +extern uintptr_t load_sz;
>  #define ARCH_PFN_OFFSET		(pfn_base)
>  #else
>  #define va_pa_offset		0
> @@ -99,6 +100,11 @@ extern unsigned long pfn_base;
>  extern unsigned long kernel_virt_addr;
>  
>  #ifdef CONFIG_64BIT
> +#define is_kernel_mapping(x)	\
> +	((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
> +#define is_linear_mapping(x)	\
> +	((x) >= PAGE_OFFSET && (x) < kernel_virt_addr)
> +
>  #define linear_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_pa_offset))
>  #ifdef CONFIG_XIP_KERNEL
>  #define kernel_mapping_pa_to_va(y)	({						\
> @@ -125,10 +131,15 @@ extern unsigned long kernel_virt_addr;
>  #endif
>  #define __va_to_pa_nodebug(x)	({						\
>  	unsigned long _x = x;							\
> -	(_x < kernel_virt_addr) ?						\
> +	is_linear_mapping(_x) ?							\
>  		linear_mapping_va_to_pa(_x) : kernel_mapping_va_to_pa(_x);	\
>  	})
>  #else
> +#define is_kernel_mapping(x)	\
> +	((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
> +#define is_linear_mapping(x)	\
> +	((x) >= PAGE_OFFSET)
> +
>  #define __pa_to_va_nodebug(x)  ((void *)((unsigned long) (x) + va_pa_offset))
>  #define __va_to_pa_nodebug(x)  ((unsigned long)(x) - va_pa_offset)
>  #endif
> diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
> index 8a303fb1ee3b..32336e8a17cb 100644
> --- a/arch/riscv/include/asm/sections.h
> +++ b/arch/riscv/include/asm/sections.h
> @@ -6,6 +6,7 @@
>  #define __ASM_SECTIONS_H
>  
>  #include <asm-generic/sections.h>
> +#include <linux/mm.h>
>  
>  extern char _start[];
>  extern char _start_kernel[];
> @@ -13,4 +14,20 @@ extern char __init_data_begin[], __init_data_end[];
>  extern char __init_text_begin[], __init_text_end[];
>  extern char __alt_start[], __alt_end[];
>  
> +static inline bool is_va_kernel_text(uintptr_t va)
> +{
> +	uintptr_t start = (uintptr_t)_start;
> +	uintptr_t end = (uintptr_t)__init_data_begin;
> +
> +	return va >= start && va < end;
> +}
> +
> +static inline bool is_va_kernel_lm_alias_text(uintptr_t va)
> +{
> +	uintptr_t start = (uintptr_t)lm_alias(_start);
> +	uintptr_t end = (uintptr_t)lm_alias(__init_data_begin);
> +
> +	return va >= start && va < end;
> +}
> +
>  #endif /* __ASM_SECTIONS_H */
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index 96e317dcab13..a2c14d4b3993 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -16,7 +16,6 @@ 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_rw_nx(unsigned long addr, int numpages);
> -void protect_kernel_text_data(void);
>  static __always_inline int set_kernel_memory(char *startp, char *endp,
>  					     int (*set_memory)(unsigned long start,
>  							       int num_pages))
> @@ -32,7 +31,6 @@ 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) {}
>  static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
>  static inline int set_kernel_memory(char *startp, char *endp,
>  				    int (*set_memory)(unsigned long start,
> @@ -42,12 +40,6 @@ static inline int set_kernel_memory(char *startp, char *endp,
>  }
>  #endif
>  
> -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> -void __init protect_kernel_linear_mapping_text_rodata(void);
> -#else
> -static inline void protect_kernel_linear_mapping_text_rodata(void) {}
> -#endif
> -
>  int set_direct_map_invalid_noflush(struct page *page);
>  int set_direct_map_default_noflush(struct page *page);
>  bool kernel_page_present(struct page *page);
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 5c6d2a1fdbc7..b0c6f372a9ec 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -289,11 +289,6 @@ void __init setup_arch(char **cmdline_p)
>  	init_resources();
>  	sbi_init();
>  
> -	if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
> -		protect_kernel_text_data();
> -		protect_kernel_linear_mapping_text_rodata();
> -	}
> -
>  #ifdef CONFIG_KASAN
>  	kasan_init();
>  #endif
> @@ -328,11 +323,10 @@ subsys_initcall(topology_init);
>  
>  void free_initmem(void)
>  {
> -	unsigned long init_begin = (unsigned long)__init_begin;
> -	unsigned long init_end = (unsigned long)__init_end;
> -
>  	if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> -		set_memory_rw_nx(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
> +		set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end),
> +				  IS_ENABLED(CONFIG_64BIT) ?
> +					set_memory_rw : set_memory_rw_nx);
>  
>  	free_initmem_default(POISON_FREE_INITMEM);
>  }
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index b3fd235ddbb6..12f956b3a674 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -455,6 +455,43 @@ asmlinkage void __init __copy_data(void)
>  }
>  #endif
>  
> +#ifdef CONFIG_STRICT_KERNEL_RWX
> +static __init pgprot_t pgprot_from_va(uintptr_t va)
> +{
> +	if (is_va_kernel_text(va))
> +		return PAGE_KERNEL_READ_EXEC;
> +
> +	/*
> +	 * In 64-bit kernel, the kernel mapping is outside the linear mapping so
> +	 * we must protect its linear mapping alias from being executed and
> +	 * written.
> +	 * And rodata section is marked readonly in mark_rodata_ro.
> +	 */
> +	if (IS_ENABLED(CONFIG_64BIT) && is_va_kernel_lm_alias_text(va))
> +		return PAGE_KERNEL_READ;
> +
> +	return PAGE_KERNEL;
> +}
> +
> +void mark_rodata_ro(void)
> +{
> +	set_kernel_memory(__start_rodata, _data, set_memory_ro);
> +	if (IS_ENABLED(CONFIG_64BIT))
> +		set_kernel_memory(lm_alias(__start_rodata), lm_alias(_data),
> +				  set_memory_ro);
> +
> +	debug_checkwx();
> +}
> +#else
> +static __init pgprot_t pgprot_from_va(uintptr_t va)
> +{
> +	if (IS_ENABLED(CONFIG_64BIT) && !is_kernel_mapping(va))
> +		return PAGE_KERNEL;
> +
> +	return PAGE_KERNEL_EXEC;
> +}
> +#endif /* CONFIG_STRICT_KERNEL_RWX */
> +
>  /*
>   * setup_vm() is called from head.S with MMU-off.
>   *
> @@ -474,7 +511,7 @@ asmlinkage void __init __copy_data(void)
>  #endif
>  
>  static uintptr_t load_pa __initdata;
> -static uintptr_t load_sz __initdata;
> +uintptr_t load_sz;
>  #ifdef CONFIG_XIP_KERNEL
>  #define load_pa        (*((uintptr_t *)XIP_FIXUP(&load_pa)))
>  #define load_sz        (*((uintptr_t *)XIP_FIXUP(&load_sz)))
> @@ -486,7 +523,8 @@ static uintptr_t xiprom_sz __initdata;
>  #define xiprom_sz      (*((uintptr_t *)XIP_FIXUP(&xiprom_sz)))
>  #define xiprom         (*((uintptr_t *)XIP_FIXUP(&xiprom)))
>  
> -static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
> +					    __always_unused bool early)
>  {
>  	uintptr_t va, end_va;
>  
> @@ -505,7 +543,8 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
>  				   map_size, PAGE_KERNEL);
>  }
>  #else
> -static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
> +					    bool early)
>  {
>  	uintptr_t va, end_va;
>  
> @@ -513,7 +552,9 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
>  	for (va = kernel_virt_addr; va < end_va; va += map_size)
>  		create_pgd_mapping(pgdir, va,
>  				   load_pa + (va - kernel_virt_addr),
> -				   map_size, PAGE_KERNEL_EXEC);
> +				   map_size,
> +				   early ?
> +					PAGE_KERNEL_EXEC : pgprot_from_va(va));
>  }
>  #endif
>  
> @@ -590,7 +631,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	 * us to reach paging_init(). We map all memory banks later
>  	 * in setup_vm_final() below.
>  	 */
> -	create_kernel_page_table(early_pg_dir, map_size);
> +	create_kernel_page_table(early_pg_dir, map_size, true);
>  
>  #ifndef __PAGETABLE_PMD_FOLDED
>  	/* Setup early PMD for DTB */
> @@ -666,22 +707,6 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  #endif
>  }
>  
> -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> -void __init protect_kernel_linear_mapping_text_rodata(void)
> -{
> -	unsigned long text_start = (unsigned long)lm_alias(_start);
> -	unsigned long init_text_start = (unsigned long)lm_alias(__init_text_begin);
> -	unsigned long rodata_start = (unsigned long)lm_alias(__start_rodata);
> -	unsigned long data_start = (unsigned long)lm_alias(_data);
> -
> -	set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
> -	set_memory_nx(text_start, (init_text_start - 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);
> -}
> -#endif
> -
>  static void __init setup_vm_final(void)
>  {
>  	uintptr_t va, map_size;
> @@ -714,21 +739,15 @@ static void __init setup_vm_final(void)
>  		map_size = best_map_size(start, end - start);
>  		for (pa = start; pa < end; pa += map_size) {
>  			va = (uintptr_t)__va(pa);
> -			create_pgd_mapping(swapper_pg_dir, va, pa,
> -					   map_size,
> -#ifdef CONFIG_64BIT
> -					   PAGE_KERNEL
> -#else
> -					   PAGE_KERNEL_EXEC
> -#endif
> -					);
>  
> +			create_pgd_mapping(swapper_pg_dir, va, pa, map_size,
> +					   pgprot_from_va(va));
>  		}
>  	}
>  
>  #ifdef CONFIG_64BIT
>  	/* Map the kernel */
> -	create_kernel_page_table(swapper_pg_dir, PMD_SIZE);
> +	create_kernel_page_table(swapper_pg_dir, PMD_SIZE, false);
>  #endif
>  
>  	/* Clear fixmap PTE and PMD mappings */
> @@ -759,39 +778,6 @@ static inline void setup_vm_final(void)
>  }
>  #endif /* CONFIG_MMU */
>  
> -#ifdef CONFIG_STRICT_KERNEL_RWX
> -void __init protect_kernel_text_data(void)
> -{
> -	unsigned long text_start = (unsigned long)_start;
> -	unsigned long init_text_start = (unsigned long)__init_text_begin;
> -	unsigned long init_data_start = (unsigned long)__init_data_begin;
> -	unsigned long rodata_start = (unsigned long)__start_rodata;
> -	unsigned long data_start = (unsigned long)_data;
> -#if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
> -	unsigned long end_va = kernel_virt_addr + load_sz;
> -#else
> -	unsigned long end_va = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> -#endif
> -
> -	set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
> -	set_memory_ro(init_text_start, (init_data_start - init_text_start) >> PAGE_SHIFT);
> -	set_memory_nx(init_data_start, (rodata_start - init_data_start) >> PAGE_SHIFT);
> -	/* rodata section is marked readonly in mark_rodata_ro */
> -	set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> -	set_memory_nx(data_start, (end_va - 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();
> -}
> -#endif
> -
>  #ifdef CONFIG_KEXEC_CORE
>  /*
>   * reserve_crashkernel() - reserves memory for crash kernel