Date:   Sun, 30 May 2021 09:52:11 +0200
From:   Alex Ghiti <alex@...ti.fr>
To:     Drew Fustini <drew@...gleboard.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jisheng Zhang <jszhang@...nel.org>,
        Zong Li <zong.li@...ive.com>, Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] riscv: Map the kernel with correct permissions the
 first time

Hi Drew,

Le 29/05/2021 à 19:46, Drew Fustini a écrit :
> On Fri, May 28, 2021 at 09:08:43PM -0700, Drew Fustini wrote:
>> On Wed, May 26, 2021 at 03:41:10PM +0200, Alexandre Ghiti 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@...ti.fr>
>>> ---
>>>
>>> Changes in v2:
>>> * Rebased on top of for-next (and "riscv: mm: fix build errors caused by
>>>    mk_pmd()")
>>> * Get rid of protect_kernel_linear_mapping_text_rodata as suggested by
>>>    Jisheng
>>> * Improve code in general compared to previous RFC
>>>
>>> Tested on:
>>>
>>> * kernel
>>> - rv32: OK
>>> - rv64: OK
>>>
>>> * kernel w/o CONFIG_STRICT_KERNEL_RWX:
>>> - rv32: OK
>>> - rv64: OK
>>>
>>> * xipkernel:
>>> - rv32: build only
>>> - rv64: OK
>>>
>>> * nommukernel:
>>> - rv64: build only
>>>
>>>   arch/riscv/include/asm/page.h       |   9 +-
>>>   arch/riscv/include/asm/sections.h   |  16 ++++
>>>   arch/riscv/include/asm/set_memory.h |   8 --
>>>   arch/riscv/kernel/setup.c           |   5 --
>>>   arch/riscv/mm/init.c                | 123 +++++++++++++++-------------
>>>   5 files changed, 89 insertions(+), 72 deletions(-)
>>>
>>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
>>> index 6e004d8fda4d..7ff5e0d81e41 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 +109,9 @@ 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 +131,13 @@ 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..6b5affecca83 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 +14,19 @@ 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)
>>> +{
>>> +	return (va >= (uintptr_t)_start && va < (uintptr_t)__init_text_begin);
>>> +}
>>> +
>>> +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));
>>> +}
>>> +
>>> +static inline bool is_va_kernel_init_text(uintptr_t va)
>>> +{
>>> +	return (va >= (uintptr_t)__init_text_begin && va < (uintptr_t)__init_data_begin);
>>> +}
>>> +
>>>   #endif /* __ASM_SECTIONS_H */
>>> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
>>> index 086f757e8ba3..ebb8516ec5bc 100644
>>> --- a/arch/riscv/include/asm/set_memory.h
>>> +++ b/arch/riscv/include/asm/set_memory.h
>>> @@ -16,22 +16,14 @@ 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);
>>>   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
>>>   
>>> -#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..96f483e7c279 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
>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>> index 2d80088f33d5..4b1bcbbd50aa 100644
>>> --- a/arch/riscv/mm/init.c
>>> +++ b/arch/riscv/mm/init.c
>>> @@ -425,6 +425,63 @@ asmlinkage void __init __copy_data(void)
>>>   }
>>>   #endif
>>>   
>>> +#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 */
>>> +}
>>> +
>>> +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
>>> +
>>> +	debug_checkwx();
>>> +}
>>> +#else /* CONFIG_STRICT_KERNEL_RWX */
>>> +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 */
>>> +
>>>   /*
>>>    * setup_vm() is called from head.S with MMU-off.
>>>    *
>>> @@ -454,7 +511,8 @@ 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 +531,7 @@ 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 +539,7 @@ 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 +616,7 @@ 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 +692,6 @@ 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 +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_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 +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
>>> -- 
>>> 2.30.2
>>>
>>>
>>> _______________________________________________
>>> linux-riscv mailing list
>>> linux-riscv@...ts.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>
>> I wanted to try testing this on the BeagleV Starlight but I could not
>> apply it cleanly against 5.13-rc3:
>>
>>    $ git am /tmp/patch.am
>>    Applying: riscv: Map the kernel with correct permissions the first time
>>    error: patch failed: arch/riscv/include/asm/page.h:95
>>    error: arch/riscv/include/asm/page.h: patch does not apply
>>    Patch failed at 0001 riscv: Map the kernel with correct permissions the first time
>>    hint: Use 'git am --show-current-patch=diff' to see the failed patch
>>    When you have resolved this problem, run "git am --continue".
>>    If you prefer to skip this patch, run "git am --skip" instead.
>>    To restore the original branch and stop patching, run "git am --abort".
>>
>> Is there another branch I should be looking at?
>>
>> thanks,
>> drew
> 
> I realized I should have using riscv/for-next but I still seem to
> encounter problem applying:
> 
>    $ git checkout -b riscv_for_next riscv/for-next
>    Branch 'riscv_for_next' set up to track remote branch 'for-next' from 'riscv'.
>    Switched to a new branch 'riscv_for_next'
>    pdp7@x1:~/dev/starfive/linux$ git status
>    On branch riscv_for_next
>    Your branch is up to date with 'riscv/for-next'.
>    
>    nothing to commit, working tree clean
> 
>    $ git log -1 --oneline
>    37a7a2a10ec5 (HEAD -> riscv_for_next, riscv/for-next) riscv: Turn has_fpu into a static key if FPU=y
> 
>    $ b4 am 20210526134110.217073-1-alex@...ti.fr
>    Looking up https://lore.kernel.org/r/20210526134110.217073-1-alex%40ghiti.fr
>    Grabbing thread from lore.kernel.org/linux-riscv
>    Analyzing 4 messages in the thread
>    ---
>    Writing ./v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx
>      [PATCH v2] riscv: Map the kernel with correct permissions the first time
>      ---
>    Total patches: 1
>    ---
>     Link: https://lore.kernel.org/r/20210526134110.217073-1-alex@ghiti.fr
>     Base: not found
>           git am ./v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx
> 
>    $ git am v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx
>    Applying: riscv: Map the kernel with correct permissions the first time
>    error: patch failed: arch/riscv/include/asm/page.h:95
>    error: arch/riscv/include/asm/page.h: patch does not apply
>    Patch failed at 0001 riscv: Map the kernel with correct permissions the first time
>    hint: Use 'git am --show-current-patch=diff' to see the failed patch
>    When you have resolved this problem, run "git am --continue".
>    If you prefer to skip this patch, run "git am --skip" instead.
>    To restore the original branch and stop patching, run "git am --abort".
> 
> Am I doing something wrong?

Sorry for that, I have another patch that I thought would not be 
necessary for this one. If you really want to try this one, you can take 
the commit 0a9416f6243a ("riscv: Factorize xip and !xip kernel address 
conversion macros") that you can find in my branch 
int/alex/riscv_not_exec_map_v2 at 
https://github.com/AlexGhiti/riscv-linux.git. But I'll send a v3 soon.

Sorry again,

Alex

> 
> Thanks,
> Drew
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

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