From: Michal Hocko Date: Wed, 14 Jun 2017 08:22:18 +0000 (+0200) Subject: x86/mmap, ASLR: Do not treat unlimited-stack tasks as legacy mmap X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=4a06370bcb674af88679a4f2c5c87c3e40688935;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git x86/mmap, ASLR: Do not treat unlimited-stack tasks as legacy mmap Since the following commit in 2008: cc503c1b43e0 ("x86: PIE executable randomization") We added a heuristics to treat applications with RLIMIT_STACK configured to unlimited as legacy. This means: a) set the mmap_base to 1/3 of address space + randomization and b) mmap from bottom to top. This makes some sense as it allows the stack to grow really large. On the other hand it reduces the address space usable for default mmaps (without address hint) quite a lot. We have received a bug report that SAP HANA workload has hit into this limitation. We could argue that the user just got what he asked for when setting up the unlimited stack but to be realistic growing stack up to 1/6 TASK_SIZE (allowed by mmap_base) is pretty much unimited in the real life. This would give mmap 20TB of additional address space which is quite nice. Especially when it is much more likely to use that address space than the reserved stack. Digging into the history the original implementation of the randomization: 8817210d4d96 ("[PATCH] x86_64: Flexmap for 32bit and randomized mappings for 64bit") didn't have this restriction. So let's try and remove this assumption - hopefully nothing breaks. Signed-off-by: Michal Hocko Acked-by: Jiri Kosina Acked-by: Oleg Nesterov Cc: Dave Jones Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: akpm@linux-foundation.org Cc: hughd@google.com Cc: linux-mm@kvack.org Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/tip-86b110d2ae6365ce91cabd37588bc8611770421a@git.kernel.org [ So I've applied this to tip:x86/mm with a wider Cc: list - if anyone objects to this change please holler. ] Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index 19ad095b41df..797295e792b2 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -74,9 +74,6 @@ static int mmap_is_legacy(void) if (current->personality & ADDR_COMPAT_LAYOUT) return 1; - if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) - return 1; - return sysctl_legacy_va_layout; }