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Date: Thu, 2 Feb 2017 17:52:56 +0530
From: Balbir Singh <bsingharora@...il.com>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: Bhupesh Sharma <bhsharma@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
kernel-hardening@...ts.openwall.com,
Anatolij Gustschin <agust@...x.de>, keescook@...omium.org,
Daniel Cashman <dcashman@...roid.com>,
Scott Wood <oss@...error.net>, Paul Mackerras <paulus@...ba.org>,
dcashman@...gle.com, Alistair Popple <alistair@...ple.id.au>,
bhupesh.linux@...il.com, Alexander Graf <agraf@...e.com>
Subject: Re: [PATCH 1/2] powerpc: mm: support ARCH_MMAP_RND_BITS
On Thu, Feb 02, 2017 at 09:23:33PM +1100, Michael Ellerman wrote:
> +config ARCH_MMAP_RND_BITS_MIN
> + # On 64-bit up to 1G of address space (2^30)
> + default 12 if 64BIT && PPC_256K_PAGES # 256K (2^18), = 30 - 18 = 12
> + default 14 if 64BIT && PPC_64K_PAGES # 64K (2^16), = 30 - 16 = 14
> + default 16 if 64BIT && PPC_16K_PAGES # 16K (2^14), = 30 - 14 = 16
> + default 18 if 64BIT # 4K (2^12), = 30 - 12 = 18
> + default ARCH_MMAP_RND_COMPAT_BITS_MIN
> +
> +config ARCH_MMAP_RND_BITS_MAX
> + # On 64-bit up to 32T of address space (2^45)
I thought it was 64T, TASK_SIZE_USER64 is 2^46?
<snip>
> I also have what I think is a better hunk for that:
>
> unsigned long arch_mmap_rnd(void)
> {
> - unsigned long rnd;
> + unsigned long shift, rnd;
>
> - /* 8MB for 32bit, 1GB for 64bit */
> + shift = mmap_rnd_bits;
> +#ifdef CONFIG_COMPAT
> if (is_32bit_task())
> - rnd = (unsigned long)get_random_int() % (1<<(23-PAGE_SHIFT));
> - else
> - rnd = (unsigned long)get_random_int() % (1<<(30-PAGE_SHIFT));
> + shift = mmap_rnd_compat_bits;
> +#endif
> +
> + rnd = (unsigned long)get_random_int() % (1 << shift);
>
> But I'm just nit picking I guess :)
>
No.. the version above is nicer IMHO
Balbir
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