Re: [PATCH 2/7] powerpc: move __end_rodata to cover arch read-only sections

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 14/09/2022 à 17:47, Nicholas Piggin a écrit :
> powerpc has a number of read-only sections and tables that are put
> after RO_DATA(). Move the __end_rodata symbol to cover these as well.
> 
> Setting memory to read-only at boot is done using __init_begin,
> change that that to use __end_rodata.

I see the idea after looking in more details in the generated code, but 
I think this commit description needs to be more explanatory.

In mm/pgtable_32.c there was a comment explaining why __init_begin is 
used. I think you need to explain why we don't want to use it anymore 
and why we can now use __end_rodata.

> 
> This also affects boot dmesg, is_kernel_rodata(), and some other checks.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>   arch/powerpc/kernel/vmlinux.lds.S        | 3 +++
>   arch/powerpc/mm/book3s32/mmu.c           | 2 +-
>   arch/powerpc/mm/book3s64/hash_pgtable.c  | 2 +-
>   arch/powerpc/mm/book3s64/radix_pgtable.c | 2 +-
>   arch/powerpc/mm/pgtable_32.c             | 5 ++---
>   5 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index fe22d940412f..90ac5ff73df2 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -210,6 +210,9 @@ SECTIONS
>   	}
>   #endif
>   
> +	. = ALIGN(PAGE_SIZE);
> +	__end_rodata = .;
> +

I think this will likely break block mapping on PPC32.

It needs to be aligned to STRICT_ALIGN_SIZE, like __init_begin is.


>   /*
>    * Init sections discarded at runtime
>    */
> diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
> index a96b73006dfb..e13b883e4e5b 100644
> --- a/arch/powerpc/mm/book3s32/mmu.c
> +++ b/arch/powerpc/mm/book3s32/mmu.c
> @@ -240,7 +240,7 @@ void mmu_mark_rodata_ro(void)
>   	for (i = 0; i < nb; i++) {
>   		struct ppc_bat *bat = BATS[i];
>   
> -		if (bat_addrs[i].start < (unsigned long)__init_begin)
> +		if (bat_addrs[i].start < (unsigned long)__end_rodata)
>   			bat[1].batl = (bat[1].batl & ~BPP_RW) | BPP_RX;
>   	}
>   
> diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c
> index ae008b9df0e6..28332001bd87 100644
> --- a/arch/powerpc/mm/book3s64/hash_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/hash_pgtable.c
> @@ -541,7 +541,7 @@ void hash__mark_rodata_ro(void)
>   	unsigned long start, end, pp;
>   
>   	start = (unsigned long)_stext;
> -	end = (unsigned long)__init_begin;
> +	end = (unsigned long)__end_rodata;
>   
>   	pp = htab_convert_pte_flags(pgprot_val(PAGE_KERNEL_ROX), HPTE_USE_KERNEL_KEY);
>   
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index 698274109c91..2305f34bcc33 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -228,7 +228,7 @@ void radix__mark_rodata_ro(void)
>   	unsigned long start, end;
>   
>   	start = (unsigned long)_stext;
> -	end = (unsigned long)__init_begin;
> +	end = (unsigned long)__end_rodata;
>   
>   	radix__change_memory_range(start, end, _PAGE_WRITE);
>   }
> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index 3ac73f9fb5d5..112af8c5447a 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -158,10 +158,9 @@ void mark_rodata_ro(void)
>   	}
>   
>   	/*
> -	 * mark .text and .rodata as read only. Use __init_begin rather than
> -	 * __end_rodata to cover NOTES and EXCEPTION_TABLE.
> +	 * mark .text and .rodata as read only.
>   	 */
> -	numpages = PFN_UP((unsigned long)__init_begin) -
> +	numpages = PFN_UP((unsigned long)__end_rodata) -
>   		   PFN_DOWN((unsigned long)_stext);
>   
>   	set_memory_ro((unsigned long)_stext, numpages);