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Date: Wed, 31 Jul 2019 10:33:22 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Alex Ghiti <alex@...ti.fr>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Luis Chamberlain <mcgrof@...nel.org>,
Christoph Hellwig <hch@....de>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Ralf Baechle <ralf@...ux-mips.org>,
Paul Burton <paul.burton@...s.com>,
James Hogan <jhogan@...nel.org>,
Palmer Dabbelt <palmer@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Kees Cook <keescook@...omium.org>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 14/14] riscv: Make mmap allocation top-down by default
On Wed, Jul 31, 2019 at 02:05:23AM -0400, Alex Ghiti wrote:
> On 7/30/19 1:51 AM, Alexandre Ghiti wrote:
> >In order to avoid wasting user address space by using bottom-up mmap
> >allocation scheme, prefer top-down scheme when possible.
> >
> >Before:
> >root@...uriscv64:~# cat /proc/self/maps
> >00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils
> >00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils
> >00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils
> >00018000-00039000 rw-p 00000000 00:00 0 [heap]
> >1555556000-155556d000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so
> >155556d000-155556e000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so
> >155556e000-155556f000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so
> >155556f000-1555570000 rw-p 00000000 00:00 0
> >1555570000-1555572000 r-xp 00000000 00:00 0 [vdso]
> >1555574000-1555576000 rw-p 00000000 00:00 0
> >1555576000-1555674000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so
> >1555674000-1555678000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so
> >1555678000-155567a000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so
> >155567a000-15556a0000 rw-p 00000000 00:00 0
> >3fffb90000-3fffbb1000 rw-p 00000000 00:00 0 [stack]
> >
> >After:
> >root@...uriscv64:~# cat /proc/self/maps
> >00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils
> >00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils
> >00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils
> >2de81000-2dea2000 rw-p 00000000 00:00 0 [heap]
> >3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0
> >3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so
> >3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so
> >3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so
> >3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0
> >3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0 [vdso]
> >3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so
> >3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so
> >3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so
> >3ff7fff000-3ff8000000 rw-p 00000000 00:00 0
> >3fff888000-3fff8a9000 rw-p 00000000 00:00 0 [stack]
> >
> >Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> >Reviewed-by: Christoph Hellwig <hch@....de>
> >Reviewed-by: Kees Cook <keescook@...omium.org>
> >Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> >---
> > arch/riscv/Kconfig | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> >diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >index 8ef64fe2c2b3..8d0d8af1a744 100644
> >--- a/arch/riscv/Kconfig
> >+++ b/arch/riscv/Kconfig
> >@@ -54,6 +54,19 @@ config RISCV
> > select EDAC_SUPPORT
> > select ARCH_HAS_GIGANTIC_PAGE
> > select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
> >+ select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
> >+ select HAVE_ARCH_MMAP_RND_BITS
> >+
> >+config ARCH_MMAP_RND_BITS_MIN
> >+ default 18 if 64BIT
> >+ default 8
> >+
> >+# max bits determined by the following formula:
> >+# VA_BITS - PAGE_SHIFT - 3
> >+config ARCH_MMAP_RND_BITS_MAX
> >+ default 33 if RISCV_VM_SV48
> >+ default 24 if RISCV_VM_SV39
> >+ default 17 if RISCV_VM_SV32
> > config MMU
> > def_bool y
>
>
> Hi Andrew,
>
> I have just seen you took this series into mmotm but without Paul's patch
> ("riscv: kbuild: add virtual memory system selection") on which this commit
> relies, I'm not sure it could
> compile without it as there is no default for ARCH_MMAP_RND_BITS_MAX.
>
Yes, this patch results in a bad configuration file.
CONFIG_ARCH_MMAP_RND_BITS_MIN=18
CONFIG_HAVE_ARCH_MMAP_RND_BITS=y
CONFIG_ARCH_MMAP_RND_BITS=0
CONFIG_ARCH_MMAP_RND_BITS=0 is outside the valid range, causing make to ask
for a valid number. Since none exists, one is stuck with something like:
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 1
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 2
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 3
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 4
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 5
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 6
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 7
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 8
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 19
Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [0] (NEW) 18
when trying to compile riscv images. Plus, of course, all automatic builders
bail out as result.
Guenter
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