linux/arch/mips
Hugh Dickins 1be7107fbe mm: larger stack guard gap, between vmas
Stack guard page is a useful feature to reduce a risk of stack smashing
into a different mapping. We have been using a single page gap which
is sufficient to prevent having stack adjacent to a different mapping.
But this seems to be insufficient in the light of the stack usage in
userspace. E.g. glibc uses as large as 64kB alloca() in many commonly
used functions. Others use constructs liks gid_t buffer[NGROUPS_MAX]
which is 256kB or stack strings with MAX_ARG_STRLEN.

This will become especially dangerous for suid binaries and the default
no limit for the stack size limit because those applications can be
tricked to consume a large portion of the stack and a single glibc call
could jump over the guard page. These attacks are not theoretical,
unfortunatelly.

Make those attacks less probable by increasing the stack guard gap
to 1MB (on systems with 4k pages; but make it depend on the page size
because systems with larger base pages might cap stack allocations in
the PAGE_SIZE units) which should cover larger alloca() and VLA stack
allocations. It is obviously not a full fix because the problem is
somehow inherent, but it should reduce attack space a lot.

One could argue that the gap size should be configurable from userspace,
but that can be done later when somebody finds that the new 1MB is wrong
for some special case applications.  For now, add a kernel command line
option (stack_guard_gap) to specify the stack gap size (in page units).

Implementation wise, first delete all the old code for stack guard page:
because although we could get away with accounting one extra page in a
stack vma, accounting a larger gap can break userspace - case in point,
a program run with "ulimit -S -v 20000" failed when the 1MB gap was
counted for RLIMIT_AS; similar problems could come with RLIMIT_MLOCK
and strict non-overcommit mode.

Instead of keeping gap inside the stack vma, maintain the stack guard
gap as a gap between vmas: using vm_start_gap() in place of vm_start
(or vm_end_gap() in place of vm_end if VM_GROWSUP) in just those few
places which need to respect the gap - mainly arch_get_unmapped_area(),
and and the vma tree's subtree_gap support for that.

Original-patch-by: Oleg Nesterov <oleg@redhat.com>
Original-patch-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Tested-by: Helge Deller <deller@gmx.de> # parisc
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-06-19 21:50:20 +08:00
..
alchemy MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
ar7 MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
ath25
ath79 MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
bcm47xx MIPS: BCM47XX: Fix button inversion for Asus WL-500W 2017-02-17 11:16:46 +00:00
bcm63xx MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
bmips
boot MIPS: .its targets depend on vmlinux 2017-06-15 11:48:15 +02:00
cavium-octeon Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-05-12 09:56:30 -07:00
cobalt
configs Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-05-12 09:56:30 -07:00
dec format-security: move static strings to const 2017-05-08 17:15:14 -07:00
emma MIPS: Avoid old-style declaration 2017-01-25 02:51:11 +01:00
fw
generic MIPS: generic/kexec: add support for a DTB passed in a separate buffer 2017-01-03 16:34:46 +01:00
include MIPS: kprobes: flush_insn_slot should flush only if probe initialised 2017-06-08 15:42:05 +02:00
jazz MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
jz4740 MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
kernel MIPS: Fix bnezc/jialc return address calculation 2017-06-15 11:47:42 +02:00
kvm KVM: add kvm_{test,clear}_request to replace {test,clear}_bit 2017-04-27 14:12:22 +02:00
lantiq MIPS: smp-mt: Use CPU interrupt controller IPI IRQ domain support 2017-04-12 23:13:13 +02:00
lasat MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
lib mips: get rid of tail-zeroing in primitives 2017-04-06 02:08:08 -04:00
loongson32 MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
loongson64 MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
math-emu MIPS: math-emu: Fix BC1EQZ and BC1NEZ condition handling 2017-04-10 11:56:09 +02:00
mm mm: larger stack guard gap, between vmas 2017-06-19 21:50:20 +08:00
mti-malta Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-05-12 09:56:30 -07:00
net MIPS: BPF: Fix multiple problems in JIT skb access helpers. 2017-04-10 11:56:05 +02:00
netlogic MIPS: Add missing include files 2017-03-08 10:38:06 +01:00
oprofile mips: sanitize __access_ok() 2017-04-06 02:08:06 -04:00
paravirt sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
pci Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-05-12 09:56:30 -07:00
pic32 MIPS: pic32mzda: Fix linker error for pic32_get_pbclk() 2017-02-17 11:14:29 +00:00
pistachio
pmcs-msp71xx MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
pnx833x
power
ralink Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-05-01 16:15:18 -07:00
rb532 MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
sgi-ip22 MIPS: Add missing include files 2017-03-08 10:38:06 +01:00
sgi-ip27 MIPS: clockevent drivers: Set ->min_delta_ticks and ->max_delta_ticks 2017-04-14 13:11:16 -07:00
sgi-ip32 MIPS: Add missing include files 2017-03-08 10:38:06 +01:00
sibyte MIPS: Sibyte: Export symbol periph_rev to sb1250-mac network driver. 2017-04-21 03:23:24 +02:00
sni
txx9 MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
vdso MIPS: VDSO: Explicitly use -fno-asynchronous-unwind-tables 2017-02-17 11:32:12 +00:00
vr41xx MIPS: Audit and remove any unnecessary uses of module.h 2017-02-14 09:00:25 +00:00
xilfpga MIPS: xilfpga: Use irqchip instead of the legacy way 2017-01-03 16:34:39 +01:00
Kbuild MIPS: Disable Werror when W= is set 2017-04-10 11:56:07 +02:00
Kbuild.platforms MIPS: generic: Convert SEAD-3 to a generic board 2016-10-06 18:04:20 +02:00
Kconfig Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2017-05-12 09:56:30 -07:00
Kconfig.debug MIPS: Sibyte: Fix Kconfig warning. 2017-04-21 03:34:01 +02:00
Makefile MIPS: generic: fix out-of-tree defconfig target builds 2017-04-11 13:17:31 +02:00
Makefile.postlink MIPS: Fix distclean with Makefile.postlink 2017-02-13 18:57:34 +00:00