Messages in this thread |  | | Date | Sat, 29 May 2021 13:38:09 -0700 (PDT) | Subject | Re: [PATCH v2] riscv: Map the kernel with correct permissions the first time | From | Palmer Dabbelt <> |
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On Fri, 28 May 2021 01:24:43 PDT (-0700), alex@ghiti.fr wrote: > Hi Christoph, > > Le 27/05/2021 à 08:35, Christoph Hellwig a écrit : >> On Wed, May 26, 2021 at 03:41:10PM +0200, Alexandre Ghiti wrote: >>> #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) >>> + >> >> Overly long lines. Independ of that complex macros are generally much >> more readable if they are written more function-like, that is the name >> and paramtes are kept on a line of their own: >> >> #define is_kernel_mapping(x) \ >> ((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz)) >> >> But what is the reason to not make them type-safe inline functions >> anyway? > > No reason. I will then make those macros inline functions and send > another patchset to make the below macro an inline function too. > >> >>> #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); \ >>> }) >> >> ... especially for something complex like this. >> >>> +static inline bool is_va_kernel_lm_alias_text(uintptr_t va) >>> +{ >>> + return (va >= (uintptr_t)lm_alias(_start) && va < (uintptr_t)lm_alias(__init_text_begin)); >> >> Overly long line as well. And useless braces. > > Ok. > >> >>> +static inline bool is_va_kernel_init_text(uintptr_t va) >>> +{ >>> + return (va >= (uintptr_t)__init_text_begin && va < (uintptr_t)__init_data_begin); >>> +} >> >> Same here. > > checkpatch does not complain about those lines which are under 100 > characters, what's the point in breaking them on multiple lines? > >> >>> +#ifdef CONFIG_STRICT_KERNEL_RWX >>> +static __init pgprot_t pgprot_from_va(uintptr_t va) >>> +{ >>> +#ifdef CONFIG_64BIT >>> + if (is_va_kernel_text(va) || is_va_kernel_init_text(va)) >>> + return PAGE_KERNEL_READ_EXEC; >>> + >>> + /* >>> + * We must mark only text as read-only as init text will get freed later >>> + * and rodata section is marked readonly in mark_rodata_ro. >>> + */ >>> + if (is_va_kernel_lm_alias_text(va)) >>> + return PAGE_KERNEL_READ; >>> + >>> + return PAGE_KERNEL; >>> +#else >>> + if (is_va_kernel_text(va)) >>> + return PAGE_KERNEL_READ_EXEC; >>> + >>> + if (is_va_kernel_init_text(va)) >>> + return PAGE_KERNEL_EXEC; >>> + >>> + return PAGE_KERNEL; >>> +#endif /* CONFIG_64BIT */ >>> +} >> >> If the entire function is different for config symbols please just >> split it into two separate functions. But to make the difference more >> clear IS_ENABLED might fit better here: >> >> static __init pgprot_t pgprot_from_va(uintptr_t va) >> { >> if (is_va_kernel_text(va)) >> return PAGE_KERNEL_READ_EXEC; >> if (is_va_kernel_init_text(va)) >> return IS_ENABLED(CONFIG_64BIT) ? >> PAGE_KERNEL_READ_EXEC : PAGE_KERNEL_EXEC; >> if (IS_ENABLED(CONFIG_64BIT) && is_va_kernel_lm_alias_text(va)) >> return PAGE_KERNEL_READ; >> return PAGE_KERNEL; >> } >> >> Preferable with comments explaining the 32-bit vs 64-bit difference. > > Ok this is more compact, I'll do that with the comment. > >> >>> +void mark_rodata_ro(void) >>> +{ >>> + unsigned long rodata_start = (unsigned long)__start_rodata; >>> + unsigned long data_start = (unsigned long)_data; >>> + unsigned long __maybe_unused lm_rodata_start = (unsigned long)lm_alias(__start_rodata); >>> + unsigned long __maybe_unused lm_data_start = (unsigned long)lm_alias(_data); >>> + >>> + set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT); >>> +#ifdef CONFIG_64BIT >>> + set_memory_ro(lm_rodata_start, (lm_data_start - lm_rodata_start) >> PAGE_SHIFT); >>> +#endif >> >> Lots of unreadable overly lone lines. Why not add a helper and do >> something like: >> >> static void set_kernel_memory_ro(char *startp, char *endp) >> { >> unsigned long start = (unsigned long)startp; >> unsigned long end = (unsigned long)endp; >> >> set_memory_ro(start, (start - end) >> PAGE_SHIFT); >> } >> >> set_kernel_memory_ro(_start_rodata, _data); >> if (IS_ENABLED(CONFIG_64BIT)) >> set_kernel_memory_ro(lm_alias(__start_rodata), lm_alias(_data)); >> >> > > Ok, that's better indeed. I will do something like that instead, to > avoid multiple versions of this helper: > > int set_kernel_memory(char *startp, char *endp, > > int (*set_memory)(unsigned long start, int > num_pages)) > >>> +static __init pgprot_t pgprot_from_va(uintptr_t va) >>> +{ >>> +#ifdef CONFIG_64BIT >>> + if (is_kernel_mapping(va)) >>> + return PAGE_KERNEL_EXEC; >>> + >>> + if (is_linear_mapping(va)) >>> + return PAGE_KERNEL; >>> + >>> + return PAGE_KERNEL; >>> +#else >>> + return PAGE_KERNEL_EXEC; >>> +#endif /* CONFIG_64BIT */ >>> +} >>> +#endif /* CONFIG_STRICT_KERNEL_RWX */ >>> + >> >> Same comment as for the other version. This could become: >> >> 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; >> } > > Ok I'll do that. > >> >>> -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) >> >> Overly long line. >> >>> 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)); >> >> Same here. But why not pass in a "pgprot_t ram_pgprot" instead of the >> bool, which would be self-documenting. > > This function is used to map the kernel mapping, the pgprot_t is then > different in create_kernel_page_table depending on the virtual address > so I can't pass a single pgprot_t for that or I would need a dummy > pgprot_t to test anyway.
Thanks. I've got a riscv-wx-mappings branch with the fix on it, I'll take this on there when we have something ready to go and then merge both into for-next so we can avoid merge conflicts.
> > Thank you for your review, > > Alex > >> >> _______________________________________________ >> linux-riscv mailing list >> linux-riscv@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-riscv >>
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