linux-toradex.git/arch/x86/include/asm/mmu_context.h, branch v4.4.86

x86/mm: Improve switch_mm() barrier comments

2016-01-31T19:28:55+00:00

commit 4eaffdd5a5fe6ff9f95e1ab4de1ac904d5e0fa8b upstream.

My previous comments were still a bit confusing and there was a
typo. Fix it up.

Reported-by: Peter Zijlstra 
Signed-off-by: Andy Lutomirski 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Dave Hansen 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Fixes: 71b3c126e611 ("x86/mm: Add barriers and document switch_mm()-vs-flush synchronization")
Link: http://lkml.kernel.org/r/0a0b43cdcdd241c5faaaecfbcc91a155ddedc9a1.1452631609.git.luto@kernel.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/mm: Add barriers and document switch_mm()-vs-flush synchronization

2016-01-31T19:28:54+00:00

commit 71b3c126e61177eb693423f2e18a1914205b165e upstream.

When switch_mm() activates a new PGD, it also sets a bit that
tells other CPUs that the PGD is in use so that TLB flush IPIs
will be sent.  In order for that to work correctly, the bit
needs to be visible prior to loading the PGD and therefore
starting to fill the local TLB.

Document all the barriers that make this work correctly and add
a couple that were missing.

Signed-off-by: Andy Lutomirski 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Dave Hansen 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Cc: linux-mm@kvack.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/ldt: Make modify_ldt() optional

2015-07-31T11:30:45+00:00

The modify_ldt syscall exposes a large attack surface and is
unnecessary for modern userspace.  Make it optional.

Signed-off-by: Andy Lutomirski 
Reviewed-by: Kees Cook 
Cc: Andrew Cooper 
Cc: Andy Lutomirski 
Cc: Boris Ostrovsky 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Jan Beulich 
Cc: Konrad Rzeszutek Wilk 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Sasha Levin 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: security@kernel.org 
Cc: xen-devel 
Link: http://lkml.kernel.org/r/a605166a771c343fd64802dece77a903507333bd.1438291540.git.luto@kernel.org
[ Made MATH_EMULATION dependent on MODIFY_LDT_SYSCALL. ]
Signed-off-by: Ingo Molnar

x86/ldt: Make modify_ldt synchronous

2015-07-31T08:23:23+00:00

modify_ldt() has questionable locking and does not synchronize
threads.  Improve it: redesign the locking and synchronize all
threads' LDTs using an IPI on all modifications.

This will dramatically slow down modify_ldt in multithreaded
programs, but there shouldn't be any multithreaded programs that
care about modify_ldt's performance in the first place.

This fixes some fallout from the CVE-2015-5157 fixes.

Signed-off-by: Andy Lutomirski 
Reviewed-by: Borislav Petkov 
Cc: Andrew Cooper 
Cc: Andy Lutomirski 
Cc: Boris Ostrovsky 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Jan Beulich 
Cc: Konrad Rzeszutek Wilk 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Sasha Levin 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: security@kernel.org 
Cc: 
Cc: xen-devel 
Link: http://lkml.kernel.org/r/4c6978476782160600471bd865b318db34c7b628.1438291540.git.luto@kernel.org
Signed-off-by: Ingo Molnar

x86, perf: Fix static_key bug in load_mm_cr4()

2015-07-10T08:24:38+00:00

Mikulas reported his K6-3 not booting. This is because the
static_key API confusion struck and bit Andy, this wants to be
static_key_false().

Reported-by: Mikulas Patocka 
Tested-by: Mikulas Patocka 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: 
Cc: Andrea Arcangeli 
Cc: Andy Lutomirski 
Cc: Arnaldo Carvalho de Melo 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Paul Mackerras 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Valdis Kletnieks 
Cc: Vince Weaver 
Cc: hillf.zj 
Fixes: a66734297f78 ("perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks")
Link: http://lkml.kernel.org/r/20150709172338.GC19282@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar

x86: Make is_64bit_mm() widely available

2015-06-09T10:24:32+00:00

The uprobes code has a nice helper, is_64bit_mm(), that consults
both the runtime and compile-time flags for 32-bit support.
Instead of reinventing the wheel, pull it in to an x86 header so
we can use it for MPX.

I prefer passing the 'mm' around to test_thread_flag(TIF_IA32)
because it makes it explicit where the context is coming from.

Signed-off-by: Dave Hansen 
Reviewed-by: Thomas Gleixner 
Cc: Andrew Morton 
Cc: Dave Hansen 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/20150607183704.F0209999@viggo.jf.intel.com
Signed-off-by: Ingo Molnar

perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks

2015-02-04T11:10:49+00:00

While perfmon2 is a sufficiently evil library (it pokes MSRs
directly) that breaking it is fair game, it's still useful, so we
might as well try to support it.  This allows users to write 2 to
/sys/devices/cpu/rdpmc to disable all rdpmc protection so that hack
like perfmon2 can continue to work.

At some point, if perf_event becomes fast enough to replace
perfmon2, then this can go.

Signed-off-by: Andy Lutomirski 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Paul Mackerras 
Cc: Arnaldo Carvalho de Melo 
Cc: Kees Cook 
Cc: Andrea Arcangeli 
Cc: Vince Weaver 
Cc: "hillf.zj" 
Cc: Valdis Kletnieks 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/caac3c1c707dcca48ecbc35f4def21495856f479.1414190806.git.luto@amacapital.net
Signed-off-by: Ingo Molnar

perf/x86: Only allow rdpmc if a perf_event is mapped

2015-02-04T11:10:47+00:00

We currently allow any process to use rdpmc.  This significantly
weakens the protection offered by PR_TSC_DISABLED, and it could be
helpful to users attempting to exploit timing attacks.

Since we can't enable access to individual counters, use a very
coarse heuristic to limit access to rdpmc: allow access only when
a perf_event is mmapped.  This protects seccomp sandboxes.

There is plenty of room to further tighen these restrictions.  For
example, this allows rdpmc for any x86_pmu event, but it's only
useful for self-monitoring tasks.

As a side effect, cap_user_rdpmc will now be false for AMD uncore
events.  This isn't a real regression, since .event_idx is disabled
for these events anyway for the time being.  Whenever that gets
re-added, the cap_user_rdpmc code can be adjusted or refactored
accordingly.

Signed-off-by: Andy Lutomirski 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Arnaldo Carvalho de Melo 
Cc: Kees Cook 
Cc: Andrea Arcangeli 
Cc: Vince Weaver 
Cc: "hillf.zj" 
Cc: Valdis Kletnieks 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/a2bdb3cf3a1d70c26980d7c6dddfbaa69f3182bf.1414190806.git.luto@amacapital.net
Signed-off-by: Ingo Molnar

x86: Add a comment clarifying LDT context switching

2015-02-04T11:10:43+00:00

The code is correct, but only for a rather subtle reason.  This
confused me for quite a while when I read switch_mm, so clarify the
code to avoid confusing other people, too.

TBH, I wouldn't be surprised if this code was only correct by
accident.

Signed-off-by: Andy Lutomirski 
Reviewed-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Kees Cook 
Cc: Andrea Arcangeli 
Cc: Vince Weaver 
Cc: "hillf.zj" 
Cc: Valdis Kletnieks 
Cc: Paul Mackerras 
Cc: Arnaldo Carvalho de Melo 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/0db86397f968996fb772c443c251415b0b430ddd.1414190806.git.luto@amacapital.net
Signed-off-by: Ingo Molnar

x86, mpx: Fix potential performance issue on unmaps

2015-01-22T20:11:06+00:00

The 3.19 merge window saw some TLB modifications merged which caused a
performance regression. They were fixed in commit 045bbb9fa.

Once that fix was applied, I also noticed that there was a small
but intermittent regression still present.  It was not present
consistently enough to bisect reliably, but I'm fairly confident
that it came from (my own) MPX patches.  The source was reading
a relatively unused field in the mm_struct via arch_unmap.

I also noted that this code was in the main instruction flow of
do_munmap() and probably had more icache impact than we want.

This patch does two things:
1. Adds a static (via Kconfig) and dynamic (via cpuid) check
   for MPX with cpu_feature_enabled().  This keeps us from
   reading that cacheline in the mm and trades it for a check
   of the global CPUID variables at least on CPUs without MPX.
2. Adds an unlikely() to ensure that the MPX call ends up out
   of the main instruction flow in do_munmap().  I've added
   a detailed comment about why this was done and why we want
   it even on systems where MPX is present.

Signed-off-by: Dave Hansen 
Cc: luto@amacapital.net
Cc: Dave Hansen 
Link: http://lkml.kernel.org/r/20150108223021.AEEAB987@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner