linux-kernel - Re: [PATCH 2/2] powerpc: Simplify and move arch_randomize

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Message-ID: <64841617-9edd-c9ac-4742-057a7c1d81fe@csgroup.eu>
Date:   Thu, 16 Dec 2021 19:21:44 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 2/2] powerpc: Simplify and move arch_randomize_brk()



Le 08/12/2021 à 15:32, Christophe Leroy a écrit :
> arch_randomize_brk() is only needed for hash on book3s/64, for other
> platforms the one provided by the default mmap layout is good enough.
> 
> Move it to hash_utils.c and use randomize_page() like the generic one.
> 
> And properly opt out the radix case instead of making an assumption
> on mmu_highuser_ssize.
> 
> Also change to a 32M range like most other architectures instead of 8M.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>   Applies on top of series "powerpc: Make hash MMU code build configurable"

I was obviously dreaming when I sent this patch.

It definitely requires CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT so 
should come at the end of the other series.

> 
>   arch/powerpc/kernel/process.c         | 41 ---------------------------
>   arch/powerpc/mm/book3s64/hash_utils.c | 19 +++++++++++++
>   2 files changed, 19 insertions(+), 41 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 984813a4d5dc..e7f809bdd433 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -34,10 +34,8 @@
>   #include <linux/ftrace.h>
>   #include <linux/kernel_stat.h>
>   #include <linux/personality.h>
> -#include <linux/random.h>
>   #include <linux/hw_breakpoint.h>
>   #include <linux/uaccess.h>
> -#include <linux/elf-randomize.h>
>   #include <linux/pkeys.h>
>   #include <linux/seq_buf.h>
>   
> @@ -2313,42 +2311,3 @@ unsigned long arch_align_stack(unsigned long sp)
>   		sp -= get_random_int() & ~PAGE_MASK;
>   	return sp & ~0xf;
>   }
> -
> -static inline unsigned long brk_rnd(void)
> -{
> -        unsigned long rnd = 0;
> -
> -	/* 8MB for 32bit, 1GB for 64bit */
> -	if (is_32bit_task())
> -		rnd = (get_random_long() % (1UL<<(23-PAGE_SHIFT)));
> -	else
> -		rnd = (get_random_long() % (1UL<<(30-PAGE_SHIFT)));
> -
> -	return rnd << PAGE_SHIFT;
> -}
> -
> -unsigned long arch_randomize_brk(struct mm_struct *mm)
> -{
> -	unsigned long base = mm->brk;
> -	unsigned long ret;
> -
> -#ifdef CONFIG_PPC_BOOK3S_64
> -	/*
> -	 * If we are using 1TB segments and we are allowed to randomise
> -	 * the heap, we can put it above 1TB so it is backed by a 1TB
> -	 * segment. Otherwise the heap will be in the bottom 1TB
> -	 * which always uses 256MB segments and this may result in a
> -	 * performance penalty.
> -	 */
> -	if (!radix_enabled() && !is_32bit_task() && (mmu_highuser_ssize == MMU_SEGSIZE_1T))
> -		base = max_t(unsigned long, mm->brk, 1UL << SID_SHIFT_1T);
> -#endif
> -
> -	ret = PAGE_ALIGN(base + brk_rnd());
> -
> -	if (ret < mm->brk)
> -		return mm->brk;
> -
> -	return ret;
> -}
> -
> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
> index eced266dc5e9..b179a001bfa4 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -37,6 +37,8 @@
>   #include <linux/cpu.h>
>   #include <linux/pgtable.h>
>   #include <linux/debugfs.h>
> +#include <linux/random.h>
> +#include <linux/elf-randomize.h>
>   
>   #include <asm/interrupt.h>
>   #include <asm/processor.h>
> @@ -2185,3 +2187,20 @@ void __init print_system_hash_info(void)
>   	if (htab_hash_mask)
>   		pr_info("htab_hash_mask    = 0x%lx\n", htab_hash_mask);
>   }
> +
> +unsigned long arch_randomize_brk(struct mm_struct *mm)
> +{
> +	/*
> +	 * If we are using 1TB segments and we are allowed to randomise
> +	 * the heap, we can put it above 1TB so it is backed by a 1TB
> +	 * segment. Otherwise the heap will be in the bottom 1TB
> +	 * which always uses 256MB segments and this may result in a
> +	 * performance penalty.
> +	 */
> +	if (is_32bit_task())
> +		return randomize_page(mm->brk, SZ_32M);
> +	else if (!radix_enabled() && mmu_highuser_ssize == MMU_SEGSIZE_1T)
> +		return randomize_page(max_t(unsigned long, mm->brk, SZ_1T), SZ_1G);
> +	else
> +		return randomize_page(mm->brk, SZ_1G);
> +}
>