linux-kernel - Re: [PATCH v3 1/6] powerpc/fsl_booke/kaslr: refactor kaslr_legal_offset() and kaslr_early

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Message-ID: <6c0b0720-6998-f43a-a2b6-0632d4df1126@c-s.fr>
Date:   Thu, 20 Feb 2020 14:40:31 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
        benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com,
        keescook@...omium.org, kernel-hardening@...ts.openwall.com,
        oss@...error.net
Cc:     linux-kernel@...r.kernel.org, zhaohongjiang@...wei.com
Subject: Re: [PATCH v3 1/6] powerpc/fsl_booke/kaslr: refactor
 kaslr_legal_offset() and kaslr_early_init()



Le 06/02/2020 à 03:58, Jason Yan a écrit :
> Some code refactor in kaslr_legal_offset() and kaslr_early_init(). No
> functional change. This is a preparation for KASLR fsl_booke64.
> 
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Scott Wood <oss@...error.net>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>   arch/powerpc/mm/nohash/kaslr_booke.c | 40 ++++++++++++++--------------
>   1 file changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/powerpc/mm/nohash/kaslr_booke.c b/arch/powerpc/mm/nohash/kaslr_booke.c
> index 4a75f2d9bf0e..07b036e98353 100644
> --- a/arch/powerpc/mm/nohash/kaslr_booke.c
> +++ b/arch/powerpc/mm/nohash/kaslr_booke.c
> @@ -25,6 +25,7 @@ struct regions {
>   	unsigned long pa_start;
>   	unsigned long pa_end;
>   	unsigned long kernel_size;
> +	unsigned long linear_sz;
>   	unsigned long dtb_start;
>   	unsigned long dtb_end;
>   	unsigned long initrd_start;
> @@ -260,11 +261,23 @@ static __init void get_cell_sizes(const void *fdt, int node, int *addr_cells,
>   		*size_cells = fdt32_to_cpu(*prop);
>   }
>   
> -static unsigned long __init kaslr_legal_offset(void *dt_ptr, unsigned long index,
> -					       unsigned long offset)
> +static unsigned long __init kaslr_legal_offset(void *dt_ptr, unsigned long random)
>   {
>   	unsigned long koffset = 0;
>   	unsigned long start;
> +	unsigned long index;
> +	unsigned long offset;
> +
> +	/*
> +	 * Decide which 64M we want to start
> +	 * Only use the low 8 bits of the random seed
> +	 */
> +	index = random & 0xFF;
> +	index %= regions.linear_sz / SZ_64M;
> +
> +	/* Decide offset inside 64M */
> +	offset = random % (SZ_64M - regions.kernel_size);
> +	offset = round_down(offset, SZ_16K);
>   
>   	while ((long)index >= 0) {
>   		offset = memstart_addr + index * SZ_64M + offset;
> @@ -289,10 +302,9 @@ static inline __init bool kaslr_disabled(void)
>   static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size,
>   						  unsigned long kernel_sz)
>   {
> -	unsigned long offset, random;
> +	unsigned long random;
>   	unsigned long ram, linear_sz;
>   	u64 seed;
> -	unsigned long index;
>   
>   	kaslr_get_cmdline(dt_ptr);
>   	if (kaslr_disabled())
> @@ -333,22 +345,12 @@ static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size
>   	regions.dtb_start = __pa(dt_ptr);
>   	regions.dtb_end = __pa(dt_ptr) + fdt_totalsize(dt_ptr);
>   	regions.kernel_size = kernel_sz;
> +	regions.linear_sz = linear_sz;
>   
>   	get_initrd_range(dt_ptr);
>   	get_crash_kernel(dt_ptr, ram);
>   
> -	/*
> -	 * Decide which 64M we want to start
> -	 * Only use the low 8 bits of the random seed
> -	 */
> -	index = random & 0xFF;
> -	index %= linear_sz / SZ_64M;
> -
> -	/* Decide offset inside 64M */
> -	offset = random % (SZ_64M - kernel_sz);
> -	offset = round_down(offset, SZ_16K);
> -
> -	return kaslr_legal_offset(dt_ptr, index, offset);
> +	return kaslr_legal_offset(dt_ptr, random);
>   }
>   
>   /*
> @@ -358,8 +360,6 @@ static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size
>    */
>   notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
>   {
> -	unsigned long tlb_virt;
> -	phys_addr_t tlb_phys;
>   	unsigned long offset;
>   	unsigned long kernel_sz;
>   
> @@ -375,8 +375,8 @@ notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
>   	is_second_reloc = 1;
>   
>   	if (offset >= SZ_64M) {
> -		tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
> -		tlb_phys = round_down(kernstart_addr, SZ_64M);
> +		unsigned long tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
> +		phys_addr_t tlb_phys = round_down(kernstart_addr, SZ_64M);

That looks like cleanup unrelated to the patch itself.

>   
>   		/* Create kernel map to relocate in */
>   		create_kaslr_tlb_entry(1, tlb_virt, tlb_phys);
> 

Christophe