Commit Graph

17 Commits

Author SHA1 Message Date
Mark Rutland
8111e67dee stackleak: add on/off stack variants
The stackleak_erase() code dynamically handles being on a task stack or
another stack. In most cases, this is a fixed property of the caller,
which the caller is aware of, as an architecture might always return
using the task stack, or might always return using a trampoline stack.

This patch adds stackleak_erase_on_task_stack() and
stackleak_erase_off_task_stack() functions which callers can use to
avoid on_thread_stack() check and associated redundant work when the
calling stack is known. The existing stackleak_erase() is retained as a
safe default.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-13-mark.rutland@arm.com
2022-05-08 01:33:09 -07:00
Mark Rutland
77cf2b6dee stackleak: rework poison scanning
Currently we over-estimate the region of stack which must be erased.

To determine the region to be erased, we scan downwards for a contiguous
block of poison values (or the low bound of the stack). There are a few
minor problems with this today:

* When we find a block of poison values, we include this block within
  the region to erase.

  As this is included within the region to erase, this causes us to
  redundantly overwrite 'STACKLEAK_SEARCH_DEPTH' (128) bytes with
  poison.

* As the loop condition checks 'poison_count <= depth', it will run an
  additional iteration after finding the contiguous block of poison,
  decrementing 'erase_low' once more than necessary.

  As this is included within the region to erase, this causes us to
  redundantly overwrite an additional unsigned long with poison.

* As we always decrement 'erase_low' after checking an element on the
  stack, we always include the element below this within the region to
  erase.

  As this is included within the region to erase, this causes us to
  redundantly overwrite an additional unsigned long with poison.

  Note that this is not a functional problem. As the loop condition
  checks 'erase_low > task_stack_low', we'll never clobber the
  STACK_END_MAGIC. As we always decrement 'erase_low' after this, we'll
  never fail to erase the element immediately above the STACK_END_MAGIC.

In total, this can cause us to erase `128 + 2 * sizeof(unsigned long)`
bytes more than necessary, which is unfortunate.

This patch reworks the logic to find the address immediately above the
poisoned region, by finding the lowest non-poisoned address. This is
factored into a stackleak_find_top_of_poison() helper both for clarity
and so that this can be shared with the LKDTM test in subsequent
patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-8-mark.rutland@arm.com
2022-05-08 01:33:08 -07:00
Mark Rutland
0cfa2ccd28 stackleak: rework stack high bound handling
Prior to returning to userspace, we reset current->lowest_stack to a
reasonable high bound. Currently we do this by subtracting the arbitrary
value `THREAD_SIZE/64` from the top of the stack, for reasons lost to
history.

Looking at configurations today:

* On i386 where THREAD_SIZE is 8K, the bound will be 128 bytes. The
  pt_regs at the top of the stack is 68 bytes (with 0 to 16 bytes of
  padding above), and so this covers an additional portion of 44 to 60
  bytes.

* On x86_64 where THREAD_SIZE is at least 16K (up to 32K with KASAN) the
  bound will be at least 256 bytes (up to 512 with KASAN). The pt_regs
  at the top of the stack is 168 bytes, and so this cover an additional
  88 bytes of stack (up to 344 with KASAN).

* On arm64 where THREAD_SIZE is at least 16K (up to 64K with 64K pages
  and VMAP_STACK), the bound will be at least 256 bytes (up to 1024 with
  KASAN). The pt_regs at the top of the stack is 336 bytes, so this can
  fall within the pt_regs, or can cover an additional 688 bytes of
  stack.

Clearly the `THREAD_SIZE/64` value doesn't make much sense -- in the
worst case, this will cause more than 600 bytes of stack to be erased
for every syscall, even if actual stack usage were substantially
smaller.

This patches makes this slightly less nonsensical by consistently
resetting current->lowest_stack to the base of the task pt_regs. For
clarity and for consistency with the handling of the low bound, the
generation of the high bound is split into a helper with commentary
explaining why.

Since the pt_regs at the top of the stack will be clobbered upon the
next exception entry, we don't need to poison these at exception exit.
By using task_pt_regs() as the high stack boundary instead of
current_top_of_stack() we avoid some redundant poisoning, and the
compiler can share the address generation between the poisoning and
resetting of `current->lowest_stack`, making the generated code more
optimal.

It's not clear to me whether the existing `THREAD_SIZE/64` offset was a
dodgy heuristic to skip the pt_regs, or whether it was attempting to
minimize the number of times stackleak_check_stack() would have to
update `current->lowest_stack` when stack usage was shallow at the cost
of unconditionally poisoning a small portion of the stack for every exit
to userspace.

For now I've simply removed the offset, and if we need/want to minimize
updates for shallow stack usage it should be easy to add a better
heuristic atop, with appropriate commentary so we know what's going on.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-7-mark.rutland@arm.com
2022-05-08 01:33:08 -07:00
Mark Rutland
1723d39d2f stackleak: clarify variable names
The logic within __stackleak_erase() can be a little hard to follow, as
`boundary` switches from being the low bound to the high bound mid way
through the function, and `kstack_ptr` is used to represent the start of
the region to erase while `boundary` represents the end of the region to
erase.

Make this a little clearer by consistently using clearer variable names.
The `boundary` variable is removed, the bounds of the region to erase
are described by `erase_low` and `erase_high`, and bounds of the task
stack are described by `task_stack_low` and `task_stack_high`.

As the same time, remove the comment above the variables, since it is
unclear whether it's intended as rationale, a complaint, or a TODO, and
is more confusing than helpful.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-6-mark.rutland@arm.com
2022-05-08 01:33:08 -07:00
Mark Rutland
9ec79840d6 stackleak: rework stack low bound handling
In stackleak_task_init(), stackleak_track_stack(), and
__stackleak_erase(), we open-code skipping the STACK_END_MAGIC at the
bottom of the stack. Each case is implemented slightly differently, and
only the __stackleak_erase() case is commented.

In stackleak_task_init() and stackleak_track_stack() we unconditionally
add sizeof(unsigned long) to the lowest stack address. In
stackleak_task_init() we use end_of_stack() for this, and in
stackleak_track_stack() we use task_stack_page(). In __stackleak_erase()
we handle this by detecting if `kstack_ptr` has hit the stack end
boundary, and if so, conditionally moving it above the magic.

This patch adds a new stackleak_task_low_bound() helper which is used in
all three cases, which unconditionally adds sizeof(unsigned long) to the
lowest address on the task stack, with commentary as to why. This uses
end_of_stack() as stackleak_task_init() did prior to this patch, as this
is consistent with the code in kernel/fork.c which initializes the
STACK_END_MAGIC value.

In __stackleak_erase() we no longer need to check whether we've spilled
into the STACK_END_MAGIC value, as stackleak_track_stack() ensures that
`current->lowest_stack` stops immediately above this, and similarly the
poison scan will stop immediately above this.

For stackleak_task_init() and stackleak_track_stack() this results in no
change to code generation. For __stackleak_erase() the generated
assembly is slightly simpler and shorter.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-5-mark.rutland@arm.com
2022-05-08 01:33:08 -07:00
Mark Rutland
ac7838b4e1 stackleak: remove redundant check
In __stackleak_erase() we check that the `erase_low` value derived from
`current->lowest_stack` is above the lowest legitimate stack pointer
value, but this is already enforced by stackleak_track_stack() when
recording the lowest stack value.

Remove the redundant check.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-4-mark.rutland@arm.com
2022-05-08 01:33:07 -07:00
Mark Rutland
a12685e2d1 stackleak: move skip_erasing() check earlier
In stackleak_erase() we check skip_erasing() after accessing some fields
from current. As generating the address of current uses asm which
hazards with the static branch asm, this work is always performed, even
when the static branch is patched to jump to the return at the end of the
function.

This patch avoids this redundant work by moving the skip_erasing() check
earlier.

To avoid complicating initialization within stackleak_erase(), the body
of the function is split out into a __stackleak_erase() helper, with the
check left in a wrapper function. The __stackleak_erase() helper is
marked __always_inline to ensure that this is inlined into
stackleak_erase() and not instrumented.

Before this patch, on x86-64 w/ GCC 11.1.0 the start of the function is:

<stackleak_erase>:
   65 48 8b 04 25 00 00    mov    %gs:0x0,%rax
   00 00
   48 8b 48 20             mov    0x20(%rax),%rcx
   48 8b 80 98 0a 00 00    mov    0xa98(%rax),%rax
   66 90                   xchg   %ax,%ax  <------------ static branch
   48 89 c2                mov    %rax,%rdx
   48 29 ca                sub    %rcx,%rdx
   48 81 fa ff 3f 00 00    cmp    $0x3fff,%rdx

After this patch, on x86-64 w/ GCC 11.1.0 the start of the function is:

<stackleak_erase>:
   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)  <--- static branch
   65 48 8b 04 25 00 00    mov    %gs:0x0,%rax
   00 00
   48 8b 48 20             mov    0x20(%rax),%rcx
   48 8b 80 98 0a 00 00    mov    0xa98(%rax),%rax
   48 89 c2                mov    %rax,%rdx
   48 29 ca                sub    %rcx,%rdx
   48 81 fa ff 3f 00 00    cmp    $0x3fff,%rdx

Before this patch, on arm64 w/ GCC 11.1.0 the start of the function is:

<stackleak_erase>:
   d503245f        bti     c
   d5384100        mrs     x0, sp_el0
   f9401003        ldr     x3, [x0, #32]
   f9451000        ldr     x0, [x0, #2592]
   d503201f        nop  <------------------------------- static branch
   d503233f        paciasp
   cb030002        sub     x2, x0, x3
   d287ffe1        mov     x1, #0x3fff
   eb01005f        cmp     x2, x1

After this patch, on arm64 w/ GCC 11.1.0 the start of the function is:

<stackleak_erase>:
   d503245f        bti     c
   d503201f        nop  <------------------------------- static branch
   d503233f        paciasp
   d5384100        mrs     x0, sp_el0
   f9401003        ldr     x3, [x0, #32]
   d287ffe1        mov     x1, #0x3fff
   f9451000        ldr     x0, [x0, #2592]
   cb030002        sub     x2, x0, x3
   eb01005f        cmp     x2, x1

While this may not be a huge win on its own, moving the static branch
will permit further optimization of the body of the function in
subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-3-mark.rutland@arm.com
2022-05-08 01:33:07 -07:00
Kees Cook
dcb85f85fa gcc-plugins/stackleak: Use noinstr in favor of notrace
While the stackleak plugin was already using notrace, objtool is now a
bit more picky.  Update the notrace uses to noinstr.  Silences the
following objtool warnings when building with:

CONFIG_DEBUG_ENTRY=y
CONFIG_STACK_VALIDATION=y
CONFIG_VMLINUX_VALIDATION=y
CONFIG_GCC_PLUGIN_STACKLEAK=y

  vmlinux.o: warning: objtool: do_syscall_64()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: do_int80_syscall_32()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: exc_general_protection()+0x22: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: fixup_bad_iret()+0x20: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: do_machine_check()+0x27: call to stackleak_track_stack() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .text+0x5346e: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x143: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x10eb: call to stackleak_erase() leaves .noinstr.text section
  vmlinux.o: warning: objtool: .entry.text+0x17f9: call to stackleak_erase() leaves .noinstr.text section

Note that the plugin's addition of calls to stackleak_track_stack() from
noinstr functions is expected to be safe, as it isn't runtime
instrumentation and is self-contained.

Cc: Alexander Popov <alex.popov@linux.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-02-03 17:02:21 -08:00
Xiaoming Ni
0df8bdd5e3 stackleak: move stack_erasing sysctl to stackleak.c
kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.

To help with this maintenance let's start by moving sysctls to places
where they actually belong.  The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we
just care about the core logic.

So move the stack_erasing sysctl from kernel/sysctl.c to
kernel/stackleak.c and use register_sysctl() to register the sysctl
interface.

[mcgrof@kernel.org: commit log update]

Link: https://lkml.kernel.org/r/20211124231435.1445213-8-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Julia Lawall <julia.lawall@inria.fr>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Qing Wang <wangqing@vivo.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-01-22 08:33:35 +02:00
Tobias Klauser
4773ef33fc stackleak: let stack_erasing_sysctl take a kernel pointer buffer
Commit 32927393dc ("sysctl: pass kernel pointers to ->proc_handler")
changed ctl_table.proc_handler to take a kernel pointer.  Adjust the
signature of stack_erasing_sysctl to match ctl_table.proc_handler which
fixes the following sparse warning:

kernel/stackleak.c:31:50: warning: incorrect type in argument 3 (different address spaces)
kernel/stackleak.c:31:50:    expected void *
kernel/stackleak.c:31:50:    got void [noderef] __user *buffer

Fixes: 32927393dc ("sysctl: pass kernel pointers to ->proc_handler")
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lkml.kernel.org/r/20200907093253.13656-1-tklauser@distanz.ch
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-19 13:13:39 -07:00
Alexander Popov
feee1b8c49 gcc-plugins/stackleak: Use asm instrumentation to avoid useless register saving
The kernel code instrumentation in stackleak gcc plugin works in two stages.
At first, stack tracking is added to GIMPLE representation of every function
(except some special cases). And later, when stack frame size info is
available, stack tracking is removed from the RTL representation of the
functions with small stack frame. There is an unwanted side-effect for these
functions: some of them do useless work with caller-saved registers.

As an example of such case, proc_sys_write without() instrumentation:
    55                      push   %rbp
    41 b8 01 00 00 00       mov    $0x1,%r8d
    48 89 e5                mov    %rsp,%rbp
    e8 11 ff ff ff          callq  ffffffff81284610 <proc_sys_call_handler>
    5d                      pop    %rbp
    c3                      retq
    0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
    66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
    00 00 00

proc_sys_write() with instrumentation:
    55                      push   %rbp
    48 89 e5                mov    %rsp,%rbp
    41 56                   push   %r14
    41 55                   push   %r13
    41 54                   push   %r12
    53                      push   %rbx
    49 89 f4                mov    %rsi,%r12
    48 89 fb                mov    %rdi,%rbx
    49 89 d5                mov    %rdx,%r13
    49 89 ce                mov    %rcx,%r14
    4c 89 f1                mov    %r14,%rcx
    4c 89 ea                mov    %r13,%rdx
    4c 89 e6                mov    %r12,%rsi
    48 89 df                mov    %rbx,%rdi
    41 b8 01 00 00 00       mov    $0x1,%r8d
    e8 f2 fe ff ff          callq  ffffffff81298e80 <proc_sys_call_handler>
    5b                      pop    %rbx
    41 5c                   pop    %r12
    41 5d                   pop    %r13
    41 5e                   pop    %r14
    5d                      pop    %rbp
    c3                      retq
    66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
    00 00

Let's improve the instrumentation to avoid this:

1. Make stackleak_track_stack() save all register that it works with.
Use no_caller_saved_registers attribute for that function. This attribute
is available for x86_64 and i386 starting from gcc-7.

2. Insert calling stackleak_track_stack() in asm:
  asm volatile("call stackleak_track_stack" :: "r" (current_stack_pointer))
Here we use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h.
The input constraint is taken into account during gcc shrink-wrapping
optimization. It is needed to be sure that stackleak_track_stack() call is
inserted after the prologue of the containing function, when the stack
frame is prepared.

This work is a deep reengineering of the idea described on grsecurity blog
  https://grsecurity.net/resolving_an_unfortunate_stackleak_interaction

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Link: https://lore.kernel.org/r/20200624123330.83226-5-alex.popov@linux.com
Signed-off-by: Kees Cook <keescook@chromium.org>
2020-06-24 07:48:28 -07:00
Anders Roxell
e9c7d65661 stackleak: Mark stackleak_track_stack() as notrace
Function graph tracing recurses into itself when stackleak is enabled,
causing the ftrace graph selftest to run for up to 90 seconds and
trigger the softlockup watchdog.

Breakpoint 2, ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:200
200             mcount_get_lr_addr        x0    //     pointer to function's saved lr
(gdb) bt
\#0  ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:200
\#1  0xffffff80081d5280 in ftrace_caller () at ../arch/arm64/kernel/entry-ftrace.S:153
\#2  0xffffff8008555484 in stackleak_track_stack () at ../kernel/stackleak.c:106
\#3  0xffffff8008421ff8 in ftrace_ops_test (ops=0xffffff8009eaa840 <graph_ops>, ip=18446743524091297036, regs=<optimized out>) at ../kernel/trace/ftrace.c:1507
\#4  0xffffff8008428770 in __ftrace_ops_list_func (regs=<optimized out>, ignored=<optimized out>, parent_ip=<optimized out>, ip=<optimized out>) at ../kernel/trace/ftrace.c:6286
\#5  ftrace_ops_no_ops (ip=18446743524091297036, parent_ip=18446743524091242824) at ../kernel/trace/ftrace.c:6321
\#6  0xffffff80081d5280 in ftrace_caller () at ../arch/arm64/kernel/entry-ftrace.S:153
\#7  0xffffff800832fd10 in irq_find_mapping (domain=0xffffffc03fc4bc80, hwirq=27) at ../kernel/irq/irqdomain.c:876
\#8  0xffffff800832294c in __handle_domain_irq (domain=0xffffffc03fc4bc80, hwirq=27, lookup=true, regs=0xffffff800814b840) at ../kernel/irq/irqdesc.c:650
\#9  0xffffff80081d52b4 in ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:205

Rework so we mark stackleak_track_stack as notrace

Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-12-05 19:31:44 -08:00
Alexander Popov
ef1a840934 stackleak: Disable function tracing and kprobes for stackleak_erase()
The stackleak_erase() function is called on the trampoline stack at the
end of syscall. This stack is not big enough for ftrace and kprobes
operations, e.g. it can be exhausted if we use kprobe_events for
stackleak_erase().

So let's disable function tracing and kprobes of stackleak_erase().

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 10e9ae9fab ("gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack")
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-11-30 09:05:07 -08:00
Alexander Popov
964c9dff00 stackleak: Allow runtime disabling of kernel stack erasing
Introduce CONFIG_STACKLEAK_RUNTIME_DISABLE option, which provides
'stack_erasing' sysctl. It can be used in runtime to control kernel
stack erasing for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-09-04 10:35:48 -07:00
Alexander Popov
c8d126275a fs/proc: Show STACKLEAK metrics in the /proc file system
Introduce CONFIG_STACKLEAK_METRICS providing STACKLEAK information about
tasks via the /proc file system. In particular, /proc/<pid>/stack_depth
shows the maximum kernel stack consumption for the current and previous
syscalls. Although this information is not precise, it can be useful for
estimating the STACKLEAK performance impact for your workloads.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-09-04 10:35:48 -07:00
Alexander Popov
10e9ae9fab gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack
The STACKLEAK feature erases the kernel stack before returning from
syscalls. That reduces the information which kernel stack leak bugs can
reveal and blocks some uninitialized stack variable attacks.

This commit introduces the STACKLEAK gcc plugin. It is needed for
tracking the lowest border of the kernel stack, which is important
for the code erasing the used part of the kernel stack at the end
of syscalls (comes in a separate commit).

The STACKLEAK feature is ported from grsecurity/PaX. More information at:
  https://grsecurity.net/
  https://pax.grsecurity.net/

This code is modified from Brad Spengler/PaX Team's code in the last
public patch of grsecurity/PaX based on our understanding of the code.
Changes or omissions from the original code are ours and don't reflect
the original grsecurity/PaX code.

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-09-04 10:35:47 -07:00
Alexander Popov
afaef01c00 x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls
The STACKLEAK feature (initially developed by PaX Team) has the following
benefits:

1. Reduces the information that can be revealed through kernel stack leak
   bugs. The idea of erasing the thread stack at the end of syscalls is
   similar to CONFIG_PAGE_POISONING and memzero_explicit() in kernel
   crypto, which all comply with FDP_RIP.2 (Full Residual Information
   Protection) of the Common Criteria standard.

2. Blocks some uninitialized stack variable attacks (e.g. CVE-2017-17712,
   CVE-2010-2963). That kind of bugs should be killed by improving C
   compilers in future, which might take a long time.

This commit introduces the code filling the used part of the kernel
stack with a poison value before returning to userspace. Full
STACKLEAK feature also contains the gcc plugin which comes in a
separate commit.

The STACKLEAK feature is ported from grsecurity/PaX. More information at:
  https://grsecurity.net/
  https://pax.grsecurity.net/

This code is modified from Brad Spengler/PaX Team's code in the last
public patch of grsecurity/PaX based on our understanding of the code.
Changes or omissions from the original code are ours and don't reflect
the original grsecurity/PaX code.

Performance impact:

Hardware: Intel Core i7-4770, 16 GB RAM

Test #1: building the Linux kernel on a single core
        0.91% slowdown

Test #2: hackbench -s 4096 -l 2000 -g 15 -f 25 -P
        4.2% slowdown

So the STACKLEAK description in Kconfig includes: "The tradeoff is the
performance impact: on a single CPU system kernel compilation sees a 1%
slowdown, other systems and workloads may vary and you are advised to
test this feature on your expected workload before deploying it".

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-09-04 10:35:47 -07:00