Messages in this thread | | | Date | Thu, 20 May 2021 00:29:09 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH RFC] riscv: Map the kernel with correct permissions the first time |
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On Tue, 18 May 2021 17:21:34 +0200 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> > --- > > This patchset was tested on: > > * kernel: > - rv32 with CONFIG_STRICT_KERNEL_RWX: OK > - rv32 without CONFIG_STRICT_KERNEL_RWX: OK > - rv64 with CONFIG_STRICT_KERNEL_RWX: OK > - rv64 without CONFIG_STRICT_KERNEL_RWX: OK > > * xipkernel: > - rv32: build only > - rv64: OK > > arch/riscv/include/asm/set_memory.h | 2 - > arch/riscv/kernel/setup.c | 1 - > arch/riscv/mm/init.c | 80 ++++++++++++++--------------- > 3 files changed, 38 insertions(+), 45 deletions(-) > > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h > index 086f757e8ba3..70154f012791 100644 > --- a/arch/riscv/include/asm/set_memory.h > +++ b/arch/riscv/include/asm/set_memory.h > @@ -16,13 +16,11 @@ 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); > #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; } > #endif > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > index 03901d3a8b02..1eb50e512056 100644 > --- a/arch/riscv/kernel/setup.c > +++ b/arch/riscv/kernel/setup.c > @@ -292,7 +292,6 @@ void __init setup_arch(char **cmdline_p) > sbi_init(); > > if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) { > - protect_kernel_text_data(); > protect_kernel_linear_mapping_text_rodata();
If we extend the idea a bit, I.E create the correct permission for alias line mapping at the first time, we can remove protect_kernel_linear_mapping_text_rodata()
PS: No matter whether it's fine to extend, the set_memory_nx() calling in protect_kernel_linear_mapping_text_rodata() is not necessary since the linear mapping for 64bit is NX from the beginning.
> } > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index 4faf8bd157ea..92b3184420a2 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -436,6 +436,36 @@ asmlinkage void __init __copy_data(void) > } > #endif > > +#ifdef CONFIG_STRICT_KERNEL_RWX > +#define is_text_va(va) ({ \ > + unsigned long _va = va; \ > + (_va < (unsigned long)__init_data_begin && _va >= (unsigned long)_start); \ > + })
It's better if is_text_va() is a inline function
> + > +static inline __init pgprot_t pgprot_from_kernel_va(uintptr_t va)
I'm not sure whether it's necessary to put __init marker to inline functions There are such issues in current riscv code, I planed to cook one patch to remove __init from inline functions.
> +{ > + return is_text_va(va) ? PAGE_KERNEL_READ_EXEC : PAGE_KERNEL;
if we extend the idea, then here we may return PAGE_KERNEL_READ, PAGE_KERNEL and PAGE_KERNEL_READ_EXEC correspondingly.
Thanks
> +} > + > +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(); > +} > +#else > +static inline __init pgprot_t pgprot_from_kernel_va(uintptr_t va) > +{ > + if (IS_ENABLED(CONFIG_32BIT)) > + return PAGE_KERNEL_EXEC; > + > + return (va < kernel_virt_addr) ? PAGE_KERNEL : PAGE_KERNEL_EXEC; > +} > +#endif > + > /* > * setup_vm() is called from head.S with MMU-off. > * > @@ -465,7 +495,8 @@ 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; > > @@ -484,7 +515,7 @@ 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; > > @@ -492,7 +523,7 @@ 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_kernel_va(va)); > } > #endif > > @@ -569,7 +600,7 @@ 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 */ > @@ -693,21 +724,15 @@ 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_kernel_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 */ > @@ -738,35 +763,6 @@ 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
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