Re: [PATCH v3 3/3] riscv: Map the kernel with correct permissions the first time

Anup Patel
2021-06-03T11:46:32Z

On Thu, Jun 3, 2021 at 2:01 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> For 64b kernels, we map all the kernel with write and execute permissions
> and afterwards remove writability from text and executability from data.
>
> For 32b 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>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
> 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 | 11 +--
> arch/riscv/mm/init.c | 102 ++++++++++++----------------
> 5 files changed, 75 insertions(+), 76 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 6e004d8fda4d..349e4f9874cc 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -95,6 +95,7 @@ extern unsigned long va_kernel_pa_offset;
> #endif
> extern unsigned long va_kernel_xip_pa_offset;
> extern unsigned long pfn_base;
> +extern uintptr_t load_sz;
> #define ARCH_PFN_OFFSET (pfn_base)
> #else
> #define va_pa_offset 0
> @@ -108,6 +109,11 @@ 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))
> #define kernel_mapping_pa_to_va(y) ({ \
> unsigned long _y = y; \
> @@ -127,10 +133,15 @@ extern unsigned long kernel_virt_addr;
>
> #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 /* CONFIG_64BIT */
> 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 7a411fed9e0e..c0b41ed218e1 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -17,13 +17,11 @@ 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);
> int set_kernel_memory(char *start, char *end, int (*set_memory)(unsigned long, int));
> -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) {}
> static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
> static inline int set_kernel_memory(char *start, char *end, int (*set_memory)(unsigned long, int))
> {
> @@ -31,12 +29,6 @@ static inline int set_kernel_memory(char *start, char *end, int (*set_memory)(un
> }
> #endif
>
> -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> -void 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 4db4d0b5911f..b3d0895ce5f7 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -290,11 +290,6 @@ 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_SWIOTLB
> swiotlb_init(1);
> #endif
> @@ -333,11 +328,9 @@ 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 2d80088f33d5..6b70c345cfc4 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -425,6 +425,42 @@ 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 64b 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.
> *
> @@ -454,7 +490,8 @@ uintptr_t xiprom, xiprom_sz;
> #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;
>
> @@ -473,7 +510,7 @@ 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;
>
> @@ -481,7 +518,7 @@ 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
>
> @@ -558,7 +595,7 @@ 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 */
> @@ -634,22 +671,6 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> #endif
> }
>
> -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> -void 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;
> @@ -682,21 +703,15 @@ 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 */
> @@ -727,35 +742,6 @@ 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;
> - unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> -
> - 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, (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();
> -}
> -#endif
> -
> #ifdef CONFIG_KEXEC_CORE
> /*
> * reserve_crashkernel() - reserves memory for crash kernel
> --
> 2.30.2