Re: linux-next: Tree for Nov 7

From: Michal Hocko
Date: Mon Nov 13 2017 - 04:42:12 EST

On Mon 13-11-17 10:20:06, Michal Hocko wrote:
> [Cc arm and ppc maintainers]

Hmm, it turned out to be a problem on other architectures as well.
CCing more maintainers. For your reference, we are talking about
http://lkml.kernel.org/r/20171023082608.6167-1-mhocko@xxxxxxxxxx
which has broken architectures which do apply aligning on the mmap
address hint without MAP_FIXED applied. See below my proposed way
around this issue because I belive that the above patch is quite
valuable on its own to be dropped for all archs.

> Thanks a lot for testing!
>
> On Sun 12-11-17 11:38:02, Joel Stanley wrote:
> > On Fri, Nov 10, 2017 at 11:00 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > > Hi Joel,
> > >
> > > On Wed 08-11-17 15:20:50, Michal Hocko wrote:
> > > [...]
> > >> > There are a lot of messages on the way up that look like this:
> > >> >
> > >> > [ 2.527460] Uhuuh, elf segement at 000d9000 requested but the
> > >> > memory is mapped already
> > >> > [ 2.540160] Uhuuh, elf segement at 000d9000 requested but the
> > >> > memory is mapped already
> > >> > [ 2.546153] Uhuuh, elf segement at 000d9000 requested but the
> > >> > memory is mapped already
> > >> >
> > >> > And then trying to run userspace looks like this:
> > >>
> > >> Could you please run with debugging patch posted
> > >> http://lkml.kernel.org/r/20171107102854.vylrtaodla63kc57@xxxxxxxxxxxxxx
> > >
> > > Did you have chance to test with this debugging patch, please?
> >
> > Lots of this:
> >
> > [ 1.177266] Uhuuh, elf segement at 000d9000 requested but the memory is mapped already, got 000dd000
> > [ 1.177555] Clashing vma [dd000, de000] flags:100873 name:(null)
>
> This smells like the problem I've expected that mmap with hint doesn't
> respect the hint even though there is no clashing mapping. The above
> basically says that we didn't map at 0xd9000 but it has placed it at
> 0xdd000. The nearest (clashing) vma is at 0xdd000 so this is our new
> mapping. find_vma returns the closest vma (with addr < vm_end) for the
> given address 0xd9000 so this address cannot be mapped by any other vma.
>
> Now that I am looking at arm's arch_get_unmapped_area it does perform
> aligning for shared vmas. We do not do that for MAP_FIXED. Powepc,
> reported earlier [1] seems to suffer from the similar problem.
> slice_get_unmapped_area alignes to slices, whatever that means.
>
> I can see two possible ways around that. Either we explicitly request
> non-aligned mappings via a special MAP_$FOO (e.g. MAP_FIXED_SAFE) or
> simply opt out from the MAP_FIXED protection via ifdefs. The first
> option sounds more generic to me but also more tricky to not introduce
> other user visible effects. The later is quite straightforward. What do
> you think about the following on top of the previous patch?
>
> It is rather terse and disables the MAP_FIXED protection for arm
> comletely because I couldn't find a way to make it conditional on
> CACHEID_VIPT_ALIASING. But this can be always handled later. I find the
> protection for other archtectures useful enough to have this working for
> most architectures now and handle others specially.
>
> [1] http://lkml.kernel.org/r/1510048229.12079.7.camel@xxxxxxxxxxxxxxxx
> ---
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 61a0cb15067e..018d041a30e6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -99,6 +99,7 @@ config ARM
select PERF_USE_VMALLOC
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
+ select ARCH_ALIGNED_MMAPS
# Above selects are sorted alphabetically; please add new ones
# according to that. Thanks.
help
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 48d91d5be4e9..eca59d27e9f1 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -72,6 +72,7 @@ config MIPS
select RTC_LIB if !MACH_LOONGSON64
select SYSCTL_EXCEPTION_TRACE
select VIRT_TO_BUS
+ select ARCH_ALIGNED_MMAPS

menu "Machine selection"

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 22f27ec8c117..8376d16e0a4a 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -40,6 +40,7 @@ config PARISC
select GENERIC_CLOCKEVENTS
select ARCH_NO_COHERENT_DMA_MMAP
select CPU_NO_EFFICIENT_FFS
+ select ARCH_ALIGNED_MMAPS

help
The PA-RISC microprocessor is designed by Hewlett-Packard and used
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 2f629e0551e9..156f69c09c7f 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -368,6 +368,7 @@ config PPC_MM_SLICES
bool
default y if PPC_STD_MMU_64
default n
+ select ARCH_ALIGNED_MMAPS

config PPC_HAVE_PMU_SUPPORT
bool
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 640a85925060..ac1d4637a728 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -49,6 +49,7 @@ config SUPERH
select HAVE_ARCH_AUDITSYSCALL
select HAVE_FUTEX_CMPXCHG if FUTEX
select HAVE_NMI
+ select ARCH_ALIGNED_MMAPS
help
The SuperH is a RISC processor targeted for use in embedded systems
and consumer electronics; it was also used in the Sega Dreamcast
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 0be3828752e5..c265dcda3d28 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -45,6 +45,7 @@ config SPARC
select CPU_NO_EFFICIENT_FFS
select LOCKDEP_SMALL if LOCKDEP
select ARCH_WANT_RELAX_ORDER
+ select ARCH_ALIGNED_MMAPS if SPARC64

config SPARC32
def_bool !64BIT
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 7ad6d77b2f22..a5cf535034d1 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -30,6 +30,7 @@ config XTENSA
select NO_BOOTMEM
select PERF_USE_VMALLOC
select VIRT_TO_BUS
+ select ARCH_ALIGNED_MMAPS if MMU
help
Xtensa processors are 32-bit RISC machines designed by Tensilica
primarily for embedded systems. These processors are both
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index a22718de42db..d23eb89f31c0 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -345,13 +345,19 @@ static unsigned long elf_vm_mmap(struct file *filep, unsigned long addr,
unsigned long size, int prot, int type, unsigned long off)
{
unsigned long map_addr;
+ unsigned long map_type = type;

/*
* If caller requests the mapping at a specific place, make sure we fail
* rather than potentially clobber an existing mapping which can have
- * security consequences (e.g. smash over the stack area).
+ * security consequences (e.g. smash over the stack area). Be careful
+ * about architectures which do not respect the address hint due to
+ * aligning restrictions for !fixed mappings.
*/
- map_addr = vm_mmap(filep, addr, size, prot, type & ~MAP_FIXED, off);
+ if (!IS_ENABLED(ARCH_ALIGNED_MMAPS))
+ map_type &= ~MAP_FIXED;
+
+ map_addr = vm_mmap(filep, addr, size, prot, map_type, off);
if (BAD_ADDR(map_addr))
return map_addr;

--
Michal Hocko
SUSE Labs