Commit Graph

6 Commits

Author SHA1 Message Date
Masahiro Yamada af2d22254e gcc-plugins: remove code for GCC versions older than 4.9
Documentation/process/changes.rst says the minimal GCC version is 4.9.
Hence, BUILDING_GCC_VERSION is greater than or equal to 4009.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201202134929.99883-1-masahiroy@kernel.org
2020-12-04 14:09:41 -08:00
Alexander Popov 8dd70543f7 gcc-plugins/stackleak: Add 'verbose' plugin parameter
Add 'verbose' plugin parameter for stackleak gcc plugin.
It can be used for printing additional info about the kernel code
instrumentation.

For using it add the following to scripts/Makefile.gcc-plugins:
  gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK) \
    += -fplugin-arg-stackleak_plugin-verbose

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Link: https://lore.kernel.org/r/20200624123330.83226-6-alex.popov@linux.com
Signed-off-by: Kees Cook <keescook@chromium.org>
2020-06-24 07:48:44 -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
Kees Cook 8d97fb393c gcc-plugins/stackleak: Avoid assignment for unused macro argument
With GCC version >= 8, the cgraph_create_edge() macro argument using
"frequency" goes unused. Instead of assigning a temporary variable for
the argument, pass the compute_call_stmt_bb_frequency() call directly
as the macro argument so that it will just not be called when it is
not wanted by the macros.

Silences the warning:

scripts/gcc-plugins/stackleak_plugin.c:54:6: warning: variable ‘frequency’ set but not used [-Wunused-but-set-variable]

Now builds cleanly with gcc-7 and gcc-9. Both boot and pass
STACKLEAK_ERASING LKDTM test.

Signed-off-by: Kees Cook <keescook@chromium.org>
2020-04-13 10:17:44 -07:00
Alexander Popov 8fb2dfb228 stackleak: Register the 'stackleak_cleanup' pass before the '*free_cfg' pass
Currently the 'stackleak_cleanup' pass deleting a CALL insn is executed
after the 'reload' pass. That allows gcc to do some weird optimization in
function prologues and epilogues, which are generated later [1].

Let's avoid that by registering the 'stackleak_cleanup' pass before
the '*free_cfg' pass. It's the moment when the stack frame size is
already final, function prologues and epilogues are generated, and the
machine-dependent code transformations are not done.

[1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-12-06 09:10:23 -08:00
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